@START@Starburst Galaxies and Ultraviolet Radiation EMBARGOED UNTIL: 2:00 P.M. (EDT) JUNE 13, 1995 CONTACT: Ray Villard Space Telescope Science Institute (Phone: 410-338-4514) Claus Leitherer Space Telescope Science Institute (Phone: 410-338-4425) PRESS RELEASE NO.: STScI-PR95-28 ASTRONOMERS RULE OUT STARBURST GALAXIES AS CONTRIBUTING TO THE FAR ULTRAVIOLET BACKGROUND Astronomers using the Hopkins Ultraviolet Telescope (HUT), flown aboard the Shuttle ASTRO-2 mission, have been able to exclude one explanation for the mysterious far ultraviolet background radiation that existed when the universe was young. They find that starburst galaxies -- galaxies forming new stars at an extremely high rate -- were largely opaque to the UV radiation from hot newborn stars embedded within them. Contrary to earlier ideas, this means that starburst galaxies did not contribute significantly to heating, or ionizing, the early universe. "Our results are an important first step toward understanding whether or not young star forming galaxies might be responsible for ionizing the early universe," says Claus Leitherer of the Space Telescope Science Institute in Baltimore, Maryland. Previously, astronomers had proposed that UV energy from quasars -- extremely bright active nuclei of young galaxies -- played a key role in heating the early universe. However, estimates of the early quasar population have always fallen short of fully explaining how the early universe could be so ionized. So, researchers have looked to other inhabitants of the early universe. Starburst galaxies appeared to be natural candidates for the generation of the ultraviolet background radiation. Although each starburst galaxy is by far less bright than a quasar, there are many more starburst galaxies in the universe than quasars. Therefore all starburst galaxies together might produce as much ultraviolet light as quasars. HUT was ideally suited to make the critical observation because it required looking at distant, early galaxies. The UV light from these galaxies is redshifted, by the expanding universe to the region of the spectrum (950 angstroms), accessible only to HUT. This wavelength is also a convenient "transparent" window to peer out of our Milky Way galaxy, which absorbs shorter wavelength UV light from young stars within our own Galaxy. The HUT research team making the observation are Claus Leitherer and Henry Ferguson (STScI); Timothy Heckman (the Johns Hopkins University); and James Lowenthal (University of California, Santa Crud). They are presenting their results at the 186th meeting of the American Astronomical Society in Pittsburgh, PA. The astronomers made spectroscopic observations of the galaxies Markarian 1267, Markarian 66, NGC 6090 and IRAS 08339+6517, all estimated to have conditions very similar to galaxies which existed when the universe was a few percent of its present age. They found that in all four galaxies, only a few percent of the UV radiation leaked out, as a result of absorption by their own interstellar gas. About 50% of the radiation would need to have escaped the candidate galaxies to contribute to the ultraviolet background. @START@Heaviest Star Known Observed from Space FOR RELEASE: 2:00 PM EDT, TUESDAY, JUNE 13, 1995 PRESS RELEASE NO.: STScI-PR95-27 HEAVIEST STAR KNOWN OBSERVED FROM SPACE Observations with the Hopkins Ultraviolet Telescope (HUT) of the most massive star currently known have revealed new features of its hot outer layers, which are being blown away from the star at speeds of up to 2300 miles per second due to its extreme luminous energy output. These features in turn provide information about physical characteristics of the star, such as its temperature, luminosity, chemical composition, age, and mass, or total amount of matter it contains. The results were presented today at the meeting of the American Astronomical Society in Pittsburgh, PA. An international collaboration consisting of Drs. Nolan R. Walborn and Knox S. Long from the Space Telescope Science Institute in Baltimore, MD, and Drs. Rolf-Peter Kudritzki and Daniel J. Lennon from Munich University, Germany, reported observations of the stellar record holder with the Hopkins Ultraviolet Telescope, which was operated from the space shuttle Endeavour last March. The HUT data show previously unseen features of the "stellar wind" of HDE 269810 in the Large Magellanic Cloud (LMC). Analysis of earlier data from the Hubble Space Telescope (HST) and the European Southern Observatory in Chile indicates that this star may be 190 times as massive as our Sun, the largest value to date. Its parent stellar system or galaxy, the LMC, is a relatively small satellite of our giant Milky Way Galaxy, at a distance of 170,000 light-years from us. (A light-year is the distance which light travels in one year at a speed of 186,000 miles per second, or about 6 trillion miles.) The Hopkins Ultraviolet Telescope is able to probe shorter ultraviolet wavelengths of light than the HST, and so it can observe spectral features not accessible to previous instruments. For instance, one of these features is produced by oxygen atoms from which five electrons have been removed; it is formed in very-high-temperature regions of the star's expanding outer layers. This expansion ejects the material from the star and it is governed by the star's mass, luminosity, and other parameters, which can be derived from the observations. Further analysis of the newly observed features will refine and confirm the extreme characteristics of HDE 269810. Massive stars have relatively short lifetimes, only a few million years compared to ten billion years for the Sun, because they burn their nuclear fuel more rapidly. They are very important components of the Universe, however, because their nuclear reactions synthesize most of the heavier chemical elements such as the iron in our bridges and our blood. These newly made elements are blasted out into space in the violent supernova explosions with which massive stars end their lives, and they mix with other interstellar material which may form new generations of stars. The material which makes up the Sun and Earth has been enriched with heavy elements made in massive stars which lived and died before our solar system formed. Because of the large distance of the LMC, it is likely that some massive stars we observe there today have already exploded, but the events are still on the way to us across the intervening distance at the speed of light. The nearest supernova to us seen since the invention of the telescope was observed in the LMC in 1987; of course, the event actually occurred there 170,000 years earlier. The initial mass of the Supernova 1987A progenitor star was only 20 times that of the Sun. Perhaps HDE 269810 will have an even more spectacular demise, although some theories suggest that a star of such extreme mass may collapse completely into a black hole and simply disappear from sight when its nuclear fuel is exhausted, without any accompanying outburst of light and matter. This work was supported by the National Aeronautics and Space Administration. For more information, contact Dr. Nolan R. Walborn (410-338-4915). @START@Hubble Identifies Population of Comets Beyond Neptune EMBARGOED UNTIL 11:00 A.M. EDT JUNE 14, 1995 CONTACT: Ray Villard Space Telescope Science Institute, Baltimore, MD (Phone: 410-338-4514) Anita Cochran University of Texas, Austin, TX (Phone: 512-471-1471) Hal Levison and Alan Stern Southwest Research Institute, Boulder, CO (Phone: 303-546-9670) Martin Duncan Queen's University, Ontario, Canada (Phone: 613-545-2712) HUBBLE IDENTIFIES A LONG-SOUGHT POPULATION OF COMETS BEYOND NEPTUNE NASA's Hubble Space Telescope has detected a long-sought population of comets dwelling at the icy fringe of the solar system. The observation, which is the astronomical equivalent to finding the proverbial needle-in-haystack, bolsters proof for a primordial comet reservoir just beyond Neptune, currently the farthest planet from the Sun. Based on the Hubble observations, a team of astronomers consisting of Anita Cochran of the University of Texas, Austin, TX, Hal Levison and Alan Stern of Southwest Research Institute, San Antonio, TX branch office in Boulder, CO, and Martin Duncan of Queen's University, Ontario, Canada, estimate the belt contains at least 200 million comets, which have remained essentially unchanged since the birth of the solar system 4.5 billion years ago. "For the first time, we have a direct handle on the population of comets in this outer region. The solar system just got a lot more interesting," said Cochran. "We now know where these short-period comets formed, and we now have a context for their role in the solar system's evolution." The existence of a comet-belt encircling our solar system -- like the rings which wrap around Saturn -- was first hypothesized more than 40 years ago by astronomer Gerard Kuiper. The so-named Kuiper Belt remained theory and conjecture until 1992, when ground-based telescopes began detecting about 20 large icy objects ranging from 60 to 200 miles in diameter. The planet Pluto is considered by astronomers to be the largest member of the Kuiper Belt region. However, researchers had to wait for Hubble Space Telescope's high spatial resolution and sensitivity before they could search for an underlying population of much smaller bodies assumed to be present -- just as there are more pebbles on the beach than boulders. "This is a striking example of what Hubble can do well," said Cochran. "We can at last identify small comet-sized objects that are just a few miles across, about the size of New York's Manhattan Island. "Cochran discussed her team's findings at a 11:00 a.m. news conference June 14, at the 186th meeting of the American Astronomical Society in Pittsburgh, PA. The team believes this apparently closes the mystery of the source of the short period comets, that orbit the Sun in less than 200 years, including such members as comet Encke, Giacobini-Zinner, and the infamous comet Shoemaker-Levy 9 that collided with the planet Jupiter in July, 1994. The comet-disk lies just beyond Neptune and might stretch 500 times farther from the Sun than Earth. This is 100 times closer to Earth than the hypothesized Oort cloud, commonly thought to be a vast repository of comets that were tossed out of the early solar system. Despite their close proximity, the Kuiper belt comets don't pose any greater threat of colliding with Earth than comets that come from much farther out, said experts. The comet nuclei are the primordial building blocks that condensed out of the cloud of gas, dust and ices that collapsed to form the Sun. "Knowing where comets come from will help constrain models for the formation of the solar system and tells us something new about where we came from," Cochran emphasized. "The Kuiper Belt is the best laboratory in the solar system for studying how planets formed," said Levison. "We believe we are seeing a region of the solar system where the accumulation of planets fizzled out." The icy nuclei are too far away to have the characteristic shell (coma) and tail of gasses and dust that are a comet's trademarks, when it swings close enough to the Sun to warm up and sublimate. Detecting these bodies in their "deep-freeze" state, at the dim horizon of the solar system, pushed Hubble Space Telescope to its performance limits. "Imagine trying to see something the size of a mountain, draped in black velvet, located four billion miles away," said Stern. The team used Hubble's Wide Field Planetary Camera 2 (WFPC 2) to observe a selected region of the sky in the constellation Taurus, that had few faint stars and galaxies that would confuse the search. The detection is based purely on a statistical approach, because the objects being discovered are so faint. The team plans to continue searching for more objects. They have already collected more images with Hubble. These additional images allow them to better quantify the number and sizes of comets in the Kuiper belt. They also will apply for more Hubble observing time in the future to probe the structure of the Kuiper belt. @START@Hubble Observes the Fire and Fury of a Stellar Birth EMBARGOED UNTIL: 2:00 P.M. (EDT) June 6, 1995 CONTACT: Don Savage NASA Headquarters, Washington, DC (Phone: 202-358-1547) Tammy Jones Goddard Space Flight Center, Greenbelt, MD (Phone: 301-286-5566) Ray Villard Space Telescope Science Institute (Phone: 410-338-4514) HUBBLE OBSERVES THE FIRE AND FURY OF A STELLAR BIRTH NASA's Hubble Space Telescope has provided a detailed look at the fitful, eruptive, and dynamic processes accompanying the final stages of a star's "construction." Images from the orbiting observatory reveal new details that will require further refinement of star formation theories, according to several independent teams of astronomers that have used Hubble to observe different embryonic stars. The Hubble observations shed new light on one of modern astronomy's central questions: how do tenuous clouds of interstellar gas and dust make stars like our Sun? "For the first time we are seeing a newborn star close up -- at the scale of our solar system -- and probing the inner workings," said Chris Burrows of the Space Telescope Science Institute,Baltimore, MD and the European Space Agency. "In doing so we will be able to create detailed models of star birth and gain a much better understanding of the formation of our Sun and planets." The Hubble images provide a dramatically clear look at a collapsing circumstellar disk of dust and gas that builds the star and provides the ingredients for a planetary system, blowtorch-like jets of hot gas funneled from deep within several embryonic systems, and machine-gun like bursts of material fired from the stars at speeds of a half-million miles per hour. The images offer clues to events that occurred in our solar system when the Sun was born 4.5 billion years ago. Astronomers commonly believe that Earth and the other eight planets condensed out of a circumstellar disk because they lie in the same plane and orbit the Sun in the same direction. According to this theory, when the Sun ignited it blew away the remaining disk, but not before the planets had formed. "The Hubble images are opening up a whole new field of stellar research for astronomers and clearing up of a decade worth of uncertainty," added Jeff Hester of Arizona State University, Tempe, AZ. "Now we can look so close to a star that many details of star birth become clear immediately." The key new details revealed by the new Hubble pictures: * Jets originate from the star and the inner parts of the disk and become confined to a narrow beam within a few billion miles of their source. It's not known how the jets are focused, or collimate One theory is that magnetic fields, generated by the star or disk, might constrain the jets. * Stars shoot out clumps of gas that might provide insights into the nature of the disk collapsing onto the star. The beaded jet structure is a "ticker tape" recording of how clumps of material have, episodically, fallen onto the star. In one case, Hubble allowed astronomers to follow the motion of the blobs and measure their velocity. * Jets "wiggle" along their multi-trillion-mile long paths, suggesting the gaseous fountains change their position and direction. The wiggles may result from the gravitational influence of one or more unseen protostellar companions. More generally, Hester emphasizes: "Disks and jets are ubiquitous in the universe. They occur over a vast range of energies and physical scales, in a variety of phenomena." Gaining an understanding of these young circumstellar structures might shed light on similar activity in a wide array of astronomical phenomena: novae, black holes, radio galaxies and quasars. "The Hubble pictures appear to exclude whole classes of models regarding jet formation and evolution," said Jon Morse of the Space Telescope Science Institute. A disk appears to be a natural outcome when a slowly rotating cloud of gas collapses under the force of gravity -- whether the gas is collapsing to form a star, or is falling onto a massive black hole. Material falling onto the star creates a jet when some of it is heated and blasted along a path that follows the star's rotation axis, like an axle through a wheel. Jets may assist star formation by carrying away excess angular momentum that otherwise would prevent material from reaching the star. Jets also provide astronomers with a unique glimpse of the inner workings of the star and disk. "Not even the Hubble Telescope can watch as material makes it final plunge onto the surface of the forming star, but the new observations are still telling us much about that process," said Hester. Burrows, Hester, Morse and their co-investigators independently observed several star birth sites in our galactic neighborhood. "All of these objects tell much the same story," Hester emphasized. "We are clearly seeing a process that is a crucial part of star formation, and not just the peculiarities of a few oddball objects." The researchers all agree that the Hubble pictures generally confirm models of star formation but will send theorists back to the drawing board to explain the details. The researchers emphasize that future models of star formation will have to take into account why jets are ejected from such a well-defined region in the disk, why jets are collimated a few billion miles out from the star, and why gas in the jets is ejected quasi-periodically. Changes are occurring so rapidly in the jets that Hubble will be able to follow their evolution of these objects over the next decade. @START@Hubble Probes the Workings of a Stellar Hydrogen-Bomb RELEASE DATE: May 22, 1995 CONTACT: Ray Villard Space Telescope Science Institute (Phone: 410-338-4514) PRESS RELEASE NO.: STScI-PF95-23 HUBBLE PROBES THE WORKINGS OF A STELLAR HYDROGEN-BOMB Peering into the heart of two recently exploded double-star systems, called cataclysmic variables, NASA's Hubble Space Telescope has surprised researchers by finding that the white dwarf stars at the heart of the fireworks are cooler than expected and spin more slowly than thought. "This calls for revision of theory," says Prof. Edward Sion of Villanova University, Villanova, PA. "Though these extremely faint explosive white dwarfs have been known about for 30 years, Hubble allows astronomers to observe them directly for the first time and provide observation evidence to test theories." Each dwarf -- incredibly dense, burned-out stars that have collapsed to the size of Earth -- is in a compact binary system, called a cataclysmic variable, where its companion is a normal star similar to, but smaller than the Sun. The stars orbit each other in less than three hours and are so close together the entire binary system would fit inside our Sun. This allows gas to flow from the normal star onto the dwarf, where it swirls into a pancake-shaped disk. When the disk of gas periodically collapses onto the white dwarf, it unleashes a burst of kinetic energy, called a dwarf nova outburst, equivalent to 100 million times the energy of all the warheads in the U.S. and Soviet nuclear arsenal, at the peak of the Cold War. Once dumped onto the dwarf s surface, hydrogen accumulates until it undergoes thermonuclear fusion reactions that eventually trigger the classical nova explosion, which is 10,000 times even more energetic than the dwarf nova outburst. After the detonation, the "fueling" of the white dwarf starts again. Sion and co-investigators studied the two best known cataclysmic variables, VW Hydri and U Geminorum. Hubble was used to make spectroscopic observations of the dwarf novae just days after their eruption, before another gas disk formed and obscured direct observation of the white dwarf. The biggest surprise is that the spin rates of the white dwarf stars, as measured by Hubble (slightly less than four minutes for U Geminorum and approximately once a minute for VW Hydri) are so slow there should be violent collisions where the gas disk crashes onto the slower moving white dwarf surface. Since the predicted x-rays from the hot (several hundred thousand to a million degrees centigrade, or greater) colliding gas has never been observed, astronomers thought that the white dwarf was spinning as fast as the disk, so that contact between the disk and surface was less violent. However, the Hubble results contradict this conclusion. "Despite the fact that several million years of accumulating the swirling gas disks should spin-up the white dwarfs, we just don't see it," says Sion. "Perhaps other mechanisms might be at work to carry away momentum, removing the spin. Their Hubble observations have also provided the first direct measurements of the cooling of the white dwarfs in response to the heating by the dwarf nova explosion. The researchers found that, even though the gaseous disk heats the white dwarf star surfaces by thousands of degrees Kelvin, this is still well below the predicted heating, according to standard theory. "Somehow this energy is dissipated across the dwarf's surface, rather than being concentrated at the zone where the disk crashes," says Sion. The Hubble results also show that the proportion of chemical elements in the dwarfs' atmospheres are significantly different from the observed proportions in the Sun's atmosphere. This is probably due to the fact that heavier elements falling onto the dwarf are pulled quickly below the surface layers by the dwarf's enormous gravitational field and turbulence associated with the accumulation of the gas disk. Further Hubble observations by the team during 1995-96 will attempt to resolve these mysteries. Their work appears in the May 10 and May 20 issues of the Astrophysical Journal Letters. The research team includes: E.M. Sion and Min Huang (Villanova University); Paula Szkody (University of Washington); Ivan Hubeny (NASA Goddard Space Flight Center); and Fuhua Cheng (University of Maryland). @START@Hubble Data Suggests Galaxies Have Giant Halos FOR RELEASE: March 31, 1995 CONTACT: Don Savage/NASA Headquarters 202-358-1547 Tammy Jones/Goddard Space Flight Center 301-286-5566 Ray Villard/Space Telescope Science Institute 410-338-4514 PRESS RELEASE NO.: STScI-PR95-22 HUBBLE DATA SUGGEST GALAXIES HAVE GIANT HALOS NASA's Hubble Space Telescope has helped solve a two-decade old cosmic mystery by showing that mysterious clouds of hydrogen in space may actually be vast halos of gas surrounding galaxies. "This conclusion runs contrary to the longstanding belief that these clouds occur in intergalactic space," says Ken Lanzetta of the State University of New York at Stony Brook. The existence of such vast halos, which extend 20 times farther than the diameter of a galaxy, might provide new insights into the evolution of galaxies and the nature of dark matter - an apparently invisible form of matter that surrounds galaxies. The possibility of galaxy halos was first proposed in 1969 by John Bahcall and Lyman Spitzer of the Institute for Advanced Study, Princeton, NJ. Previous observations with ground-based telescopes, the International Ultraviolet Explorer satellite, and Hubble have suggested that these clouds might be galaxy halos. However, the latest results are the most definitive finding yet, says Lanzetta, because they come from a large sample of 46 galaxies. For the past two decades, observations with ground-based telescopes have shown that the light from distant quasars (the bright cores of active galaxies) is affected by intervening gas clouds. These clouds are invisible, but betray their presence by absorbing certain frequencies, or colors, of a quasar's light. When a quasar's light is spread out into a spectrum, the missing wavelengths appear as a complex "thicket" of absorption features. Ground-based observations also showed that the number of these clouds rapidly rises out to greater distance. One possible explanation was that these were primordial clumps of gas that dissipated over time. However, in 1991, independent observations made with Hubble's Faint Object Spectrograph and Goddard High Resolution Spectrograph instruments detected more than a dozen hydrogen clouds within less than a billion light-years of our galaxy. These clouds could not be detected previously because they are only visible in the ultraviolet part of the spectrum, which is inaccessible with ground-based telescopes. This gave astronomers a powerful opportunity to further test the halo theory by imaging nearby galaxies and attempting to match them with nearby clouds. Lanzetta, David Bowen of the Space Telescope Science Institute (STScI), Baltimore, MD, David Tyler of the University of California at San Diego, and John Webb of the University on New South Wales, Australia, attempted to match galaxies and clouds by first collecting Hubble archival data on six quasars. Next, using telescopes at the National Optical Astronomy Observatory, the Anglo Australian Observatory, the Lick Observatory and the Isaac Newton Telescope, they identified galaxies near the clouds and measured distances. In the majority of cases they found galaxies within about 500,000 light-years of the clouds. "These results are a surprise. We have never seen these halos in the local universe," said David Bowen of STScI. The results explain why so many clouds are seen at greater distances: the light from distant quasars was more likely to pass through a galaxy's halo because the halo is so large. These results appear in the April 1 issue of the Astrophysical Journal. The researchers plan to extend their research to a larger sample of galaxy/cloud pairs. @START@Hubble Discovers New Dark Spot on Neptune EMBARGOED UNTIL: 2:00 P.M. EDT April 19, 1995 CONTACT: Don Savage NASA Headquarters, Washington, DC (Phone: 202-358-1547) Tammy Jones Goddard Space Flight Center, Greenbelt, MD (Phone: 301-286-5566) Ray Villard Space Telescope Science Institute (410-338-4514) RELEASE NO.: STScI-PR95-21 HUBBLE DISCOVERS NEW DARK SPOT ON NEPTUNE The distant, blue-green planet Neptune has again surprised astronomers with the emergence of a new great dark spot in the cloudy planet's northern hemisphere. The feature was discovered by NASA's Hubble Space Telescope. Only last June, Hubble images revealed that a great dark spot in the southern hemisphere - discovered by the Voyager 2 spacecraft during its 1989 flyby - had mysteriously disappeared. The new dark spot is a near mirror-image of the previous feature first mapped by Voyager 2. The northern dark spot discovered by Hubble is accompanied by bright, high-altitude clouds. As atmospheric gasses flow up over the spot, they cool to form these methane-ice crystal clouds. "Hubble is showing us that Neptune has changed radically since 1989," said Heidi Hammel of the Massachusetts Institute of Technology. "New features like this indicate that with Neptune's extraordinary dynamics, the planet can look completely different in just a few weeks." Like its predecessor, the new spot might be a hole in Neptune's methane cloud tops that gives a peek to lower levels of the atmosphere. "We weren t surprised the other spot disappeared, "said Hammel. "It was kind of 'floppy' because it changed shape as atmospheric circulation carried it around the planet." (By contrast, Jupiter's Great Red Spot, which is similar to Neptune's original spot in relative size and position, has remained stable in appearance for at least 300 years.) Hammel points out that studying the dynamics of Neptune's immense atmosphere might lead to a better understanding of Earth's atmosphere. "Neptune's unusual behavior is showing us that though we can make great models of planetary atmospheric circulation, there may be key pieces missing." Energy from the Sun drives Earth's weather system. However, the mechanism must be very different on Neptune because the planet radiates 2 times more energy than it receives from the distant, dim Sun. Neptune's atmosphere might be so dynamic because the cloud tops are warmed from below by this strong internal heat source. A slight change in the temperature differential from cloud bottom to top might trigger rapid, large-scale changes in atmospheric circulation. Since the 1989 Voyager flyby, astronomers using ground-based telescopes have not been able to resolve the subtle structures in Neptune's variable atmosphere, particularly the low-contrast dark features. The astronomers don t know how long the new feature will last. For the first time in planetary history though, Hubble will allow astronomers to follow the details of Neptune's atmospheric changes over at least a decade. @START@Vesta: Asteroid or Mini-Planet? EMBARGOED UNTIL: 2:00 PM EDT April 19, 1995 CONTACT: Don Savage NASA Headquarters, Washington, DC (Phone: 202-358-1547) Tammy Jones Goddard Space Flight Center, Greenbelt, MD (Phone: 301-286-5566) Ray Villard Space Telescope Science Institute (Phone: 410-338-4514) PRESS RELEASE NO.: STScI-PR95-20 ASTEROID OR MINI-PLANET? HUBBLE MAPS THE ANCIENT SURFACE OF VESTA NASA's Hubble Space Telescope images of the asteroid Vesta are providing astronomers with a glimpse of the oldest terrain ever seen in the solar system and a peek into a broken off section of the "mini-planet" that exposes its interior. Hubble's pictures provide the best view yet of Vesta's complex surface, with a geology similar to that of terrestrial worlds such as Earth or Mars. The asteroid's ancient surface, battered by collisions eons ago, allows astronomers to peer below the asteroid's crust and into the past. Astronomers also believe that fragments gouged out of Vesta during ancient collisions have fallen to Earth as meteorites, making Vesta only the fourth solar system object, other than Earth, the Moon and Mars, where scientists have a confirmed laboratory sample. (About 50-60 other meteorite types are suspected to have come from asteroids, but positive identifications are more difficult to make.) "The Hubble observations show that Vesta is far more interesting than simply a chunk of rock in space as most asteroids are," said Ben Zellner of Georgia Southern University. "This qualifies Vesta as the 'sixth' terrestrial planet." No bigger than the state of Arizona, Vesta offers new clues to the origin of the solar system and the interior makeup of the rocky planets. "Vesta has survived essentially intact since the formation of the planets," Zellner said. "It provides a record of the long and complex evolution of our solar system." Resolving features down to 50 miles across, Hubble reveals a surprisingly diverse world with an exposed mantle, ancient lava flows and impact basins. Though only 325 miles (525 kilometers) across, it once had a molten interior. This contradicts conventional ideas that asteroids essentially are cold, rocky fragments left behind from the early days of planetary formation. Besides providing scientists with direct samples, Vesta's chipped surface allows Hubble to study the asteroid's rocky mantle, giving scientists a unique opportunity to see what a planet looks like below the crust. "Our knowledge of the interior composition of the other terrestrial worlds, the Moon, Mars, Venus, Mercury and even Earth, depends heavily on theory and inference," Zellner said. "Vesta allows us to actually see the mantle and study pristine samples in our laboratories." Before these observations, only the smaller and less geologically diverse asteroids, Ida and Gaspra, have been observed in detail by the Jupiter-bound Galileo spacecraft. Unlike Vesta, these smaller objects are pieces torn off larger bodies by collisions that occurred perhaps only a few hundred million years ago. @START@1995 Hubble Fellows to Study HST Discoveries CONTACT: Cheryl Gundy FOR RELEASE: March 31, 1995 410-338-4707 PRESS RELEASE NO.: STScI-PR95-19 1995 HUBBLE FELLOWS TO STUDY HST DISCOVERIES The Space Telescope Science Institute (STScI) has selected 12 young scientists for the 1995 Hubble Postdoctoral Fellowship Program. The awardees were selected from a pool of applications from highly qualified candidates worldwide. Inaugurated in 1990, the Hubble Fellowship Program funds research opportunities for a significant fraction of the approximately 200 Ph.D. astronomers who graduate annually. The program is a joint venture between NASA and STScI, in cooperation with astronomical institutions across the United States. The scientists selected for this program will have an opportunity to conduct Hubble Space Telescope (HST)-related research of their choice at participating astronomical institutions throughout the U.S. In order to avoid an excessive concentration of talent at any one astronomy institution, no more than one new Fellow per year is approved for any one place. New Hubble Fellows are added each year, for three-year terms. The program currently supports a pool of several dozen astronomers. Candidates are selected each year through a review by a 10 member panel composed of eminent scientists from U.S. institutions, which ranks them on the basis of merit (research proposal, publications, academic achievements), after which the STScI director or his designate makes the final selection. On completion of the Fellowship Program, these young astronomers are expected to go on to professorships at major institutions. The Hubble Fellowship Program is expected to play an important role in expanding and strengthening the astronomical community. "The Hubble Fellowships not only fund excellent scientific research, but also bring the best and brightest into the nation's centers of higher education," said Peter Stockman, deputy director of STScI. "We expect that many of the Hubble Fellows will become tomorrow's top scientists and educators." The 1995 Hubble Fellowship recipients and the institutions where they will conduct their research are: Robert Blum, Joint Institute for Laboratory Astrophysics, University of Colorado, Boulder, CO; Michael Eracleous, University of California, Berkeley, CA; Philippe Fischer, University of Michigan, Ann Arbor, MI; Adam Frank, University of Minnesota, Minneapolis, MN; Mauro Giavalisco, Observatories of the Carnegie Institution of Washington, Pasadena, CA; and Margaret Hanson, Steward Observatory, University of Arizona, Tucson, AZ. Other recipients are: Inger Jorgensen, University of Texas, Austin, TX; James Mihos, The Johns Hopkins University, Baltimore, MD; Michael Rauch, California Institute of Technology, Pasadena, CA; Katherine Roth, Institute for Astronomy, University of HI, Honolulu, Hawaii; Ata Sarajedini, Kitt Peak National Observatory, Tucson, AZ; and Michael Vogeley, Space Telescope Science Institute, Baltimore, MD. @START@Hubble Tracks Jupiter Storms PHOTO FILE NO.: STScI-PF95-18 RELEASE DATE: March 31, 1995 HUBBLE TRACKS JUPITER STORMS NASA's Hubble Space Telescope is following dramatic and rapid changes in Jupiter's turbulent atmosphere that will be critical for targeting observations made by the Galileo space probe when it arrives at the giant planet later this year. This Hubble image provides a detailed look at a unique cluster of three white oval-shaped storms that lie southwest (below and to the left) of Jupiter's Great Red Spot. The appearance of the clouds, as imaged on February 13, 1995 is considerably different from their appearance only seven months earlier. Hubble shows these features moving closer together as the Great Red Spot is carried westward by the prevailing winds while the white ovals are swept eastward. (This change in appearance is not an effect of last July's comet Shoemaker- Levy 9 collisions with Jupiter.) The outer two of the white storms formed in the late 1930s. In the centers of these cloud systems the air is rising, carrying fresh ammonia gas upward. New, white ice crystals form when the upwelling gas freezes as it reaches the chilly cloud top level where temperatures are -200 degrees Fahrenheit (-130 degrees Centigrade). The intervening white storm center, the ropy structure to the left of the ovals, and the small brown spot have formed in low pressure cells. The white clouds sit above locations where gas is descending to lower, warmer regions. The extent of melting of the white ice exposes varied amounts of Jupiter's ubiquitous brown haze. The stronger the down flow, the less ice, and the browner the region. A scheduled series of Hubble observations will help target regions of interest for detailed scrutiny by the Galileo spacecraft, which will arrive at Jupiter in early December 1995. Hubble will provide a global view of Jupiter while Galileo will obtain close-up images of structure of the clouds that make up the large storm systems such as the Great Red Spot and white ovals that are seen in this picture. This color picture is assembled from a series of images taken by the Wide Field Planetary Camera 2, in planetary camera mode, when Jupiter was at a distance of 519 million miles (961 million kilometers) from Earth. These images are part of a set of data obtained by a Hubble Space Telescope (HST) team headed by Reta Beebe of New Mexico State University. Credit: Reta Beebe, Amy Simon (New Mexico State Univ.), and NASA @START@Hubble Monitors Weather on Neighboring Planets Don Savage NASA Headquarters, Washington, DC (Phone: 202-358-1547) EMBARGOED UNTIL: 2:00 P.M. EST March 21, 1995 Tammy Jones Goddard Space Flight Center, Greenbelt, MD (Phone: 301-286-5566) Ray Villard RELEASE NO: STScI-PR95-16 Space Telescope Science Institute, Baltimore, MD (Phone: 410-338-4514) HUBBLE MONITORS WEATHER ON NEIGHBORING PLANETS "The weather on Mars: another cool and clear day. Low morning haze will give way to a mostly sunny afternoon with high clouds. The forecast for Venus: hot, overcast, sulfuric acid showers will continue. Air quality is slightly improved as smog levels subside." NASA's Hubble Space Telescope is serving as an interplanetary weather satellite for studying the climate on Earth's neighboring worlds, Mars and Venus. To the surprise of researchers, Hubble is showing that the Martian climate has changed considerably since the unmanned Viking spacecraft visited Mars in the mid-1970s, which was the last time astronomers got a close-up look at weather on the Red Planet for more than just a few months. Hubble images of fleecy clouds, and spectroscopic detection of an ozone abundance in Mars' atmosphere, all indicate that the planet is cooler, clearer and drier than a couple of decades ago. In striking contrast, Hubble's spectroscopic observations of Venus show that the atmosphere continues to recover from an intense bout of sulfuric "acid rain" triggered by the suspected eruption of a volcano in the late 1970s. This is similar to what happens on Earth when sulfur dioxide emissions from coal power plants are broken apart in the atmosphere to make acid rain. On Venus, this effect takes place on a planetary scale. Although the close-up visits by numerous unmanned spacecraft provided brief snapshot glimpses of weather on these planets, the long-term coverage offered by Hubble has never before been possible. Knowledge about the weather is critical to planning future missions to these worlds. In the case of Mars, being able to predict the weather will be critical prior to human exploration and, perhaps eventually, colonization. Studying conditions on Mars and Venus might also lead to a better understanding of Earth's weather system. Apparently, processes that occurred early in the solar system's history sent terrestrial planets along very different evolutionary paths. The neighboring planets are grand natural laboratories for testing computer models that will lead to a general theory of the behavior of planetary atmospheres. @START@Hubble Views Distant Galaxies Through a Cosmic Lens PHOTO FILE NO.: STScI-PF95-14 FOR RELEASE: APRIL 5, 1995 HUBBLE VIEWS DISTANT GALAXIES THROUGH A COSMIC LENS This NASA Hubble Space Telescope image of the rich galaxy cluster, Abell 2218, is a spectacular example of gravitational lensing. The arc-like pattern spread across the picture like a spider web is an illusion caused by the gravitational field of the cluster. The cluster is so massive and compact that light rays passing through it are deflected by its enormous gravitational field, much as an optical lens bends light to form an image. The process magnifies, brightens and distorts images of objects that lie far beyond the cluster. This provides a powerful "zoom lens" for viewing galaxies that are so far away they could not normally be observed with the largest available telescopes. Hubble's high resolution reveals numerous arcs which are difficult to detect with ground-based telescopes because they appear to be so thin. The arcs are the distorted images of a very distant galaxy population extending 5-10 times farther than the lensing cluster. This population existed when the universe was just one quarter of its present age. The arcs provide a direct glimpse of how star forming regions are distributed in remote galaxies, and other clues to the early evoution of galaxies. Hubble also reveals multiple imaging, a rarer lensing event that happens when the distortion is large enough to produce more than one image of the same galaxy. Abell 2218 has an unprecedented total of seven multiple systems. The abundance of lensing features in Abell 2218 has been used to make a detailed map of the distribution of matter in the cluster's center. From this, distances can be calculated for a sample of 120 faint arclets found on the Hubble image. These arclets represent galaxies that are 50 times fainter than objects that can be seen with ground-based telescopes. Studies of remote galaxies viewed through well-studied lenses like Abell 2218 promise to reveal the nature of normal galaxies at much earlier epochs than was previously possible. The technique is a powerful combination of Hubble's superlative capabilities and the "natural" focusing properties of massive clusters like Abell 2218. The image was taken with the Wide Field Planetary Camera 2. Credits: W.Couch (University of New South Wales), R. Ellis (Cambridge University), and NASA @START@Oxygen-Rich Supernova Remnant in the LMC PHOTO FILE NO.: STScI-PF95-13 FOR RELEASE: April 10, 1995 OXYGEN-RICH SUPERNOVA REMNANT IN THE LARGE MAGELLANIC CLOUD This is a NASA Hubble Space Telescope image of the tattered debris of a star that exploded 3,000 years ago as a supernova. This supernova remnant, called N132D, lies 169,000 light-years away in the satellite galaxy, the Large Magellanic Cloud. A Hubble Wide Field Planetary Camera 2 image of the inner regions of the supernova remnant shows the complex collisions that take place as fast moving ejecta slam into cool, dense interstellar clouds. This level of detail in the expanding filaments could only be seen previously in much closer supernova remnants. Now, Hubble's capabilities extend the detailed study of supernovae out to the distance of a neighboring galaxy. Material thrown out from the interior of the exploded star at velocities of more than four million miles per hour (2,000 kilometers per second) plows into neighboring clouds to create luminescent shock fronts. The blue-green filaments in the image correspond to oxygen-rich gas ejected from the core of the star. The oxygen-rich filaments glow as they pass through a network of shock fronts reflected off dense interstellar clouds that surrounded the exploded star. These dense clouds, which appear as reddish filaments, also glow as the shock wave from the supernova crushes and heats the clouds. Supernova remnants provide a rare opportunity to observe directly the interiors of stars far more massive than our Sun. The precursor star to this remnant, which was located slightly below and left of center in the image, is estimated to have been 25 times the mass of our Sun. These stars "cook" heavier elements through nuclear fusion, including oxygen, nitrogen, carbon, iron etc., and the titanic supernova explosions scatter this material back into space where it is used to create new generations of stars. This is the mechanism by which the gas and dust that formed our solar system became enriched with the elements that sustain life on this planet. Hubble spectroscopic observations will be used to determine the exact chemical composition of this nuclear- processed material, and thereby test theories of stellar evolution. The image shows a region of the remnant 50 light-years across. The supernova explosion should have been visible from Earth's southern hemisphere around 1,000 B.C., but there are no known historical records that chronicle what would have appeared as a "new star" in the heavens. This "true color" picture was made by superposing images taken on 9-10 August 1994 in three of the strongest optical emission lines: singly ionized sulfur (red), doubly ionized oxygen (green), and singly ionized oxygen (blue). Photo credit: Jon A. Morse (STScI) and NASA Investigating team: William P. Blair (PI; JHU), Michael A. Dopita (MSSSO), Robert P. Kirshner (Harvard), Knox S. Long (STScI), Jon A. Morse (STScI), John C. Raymond (SAO), Ralph S. Sutherland (UC-Boulder), and P. Frank Winkler (Middlebury). @START@Hubble Finds Oxygen Atmosphere on Europa Contact: Ray Villard/STScI FOR RELEASE: February 23, 1995 (410) 338-4514 PRESS RELEASE NO.: STScI-PR95-12 Dr. Doyle Hall/JHU (410) 516-7338 HUBBLE FINDS OXYGEN ATMOSPHERE ON JUPITER'S MOON EUROPA Astronomers using NASA's Hubble Space Telescope (HST) have identified the presence of an extremely tenuous atmosphere of molecular oxygen around Jupiter's moon, Europa. This makes Europa the first satellite ever found to have an oxygen atmosphere, and only the third such solar system object beyond Earth (the planets Mars and Venus have traces of molecular oxygen in their atmospheres). This detection was made by a team of researchers at the Johns Hopkins University and the Space Telescope Science Institute, both in Baltimore, Maryland, and is reported in the February 23, 1995 issue of the journal Nature. "Europa's oxygen atmosphere is so tenuous that its surface pressure is barely one hundred billionth that of the Earth," says principal investigator Doyle Hall, of Johns Hopkins. "It is truly amazing that the Hubble Space Telescope can detect such a wispy gas so far away." If all the oxygen on Europa were compressed to the surface pressure of Earth's atmosphere, it would fill only about a dozen Astrodome-sized stadiums. The HST researchers caution that the detection should not be misinterpreted as evidence for the presence of life on the small, frigid moon. Located 5 times farther from the Sun than Earth, Europa is too cold, measured at -230 degrees Fahrenheit (-145 degrees Celsius), to support life as we know it. Unlike Earth, where organisms generate and maintain a 21% oxygen atmosphere, Europa's oxygen atmosphere is produced by purely non-biological processes. Europa's icy surface is exposed to sunlight and is impacted by dust and charged particles trapped within Jupiter's intense magnetic field. Combined, these processes cause the frozen water ice on the surface to produce water vapor as well as gaseous fragments of water molecules. After the gas molecules are produced, they undergo a series of chemical reactions that ultimately form molecular hydrogen and oxygen. The relatively lightweight hydrogen gas escapes into space, while the heavier oxygen molecules accumulate to form an atmosphere which may extend 125 miles (200 kilometers) above the surface. The oxygen gas slowly leaks into space and must be replenished continuously. Europa is approximately the size of Earth's Moon, but its appearance and composition are markedly different. The satellite has an unusually smooth and nearly craterless surface of solid water ice. Mysterious dark markings crisscross the surface, giving the moon a "cracked eggshell" appearance. Under the apparently fragmented icy crust, tidal heating by Jupiter might heat the icy material enough to maintain a subsurface ocean of liquid water. Of the 61 identified moons in the solar system, only three other satellites are known to have atmospheres: Jupiter's volcanically active moon Io (sulfur dioxide), Saturn's largest moon Titan (nitrogen/methane) and Neptune's largest moon Triton (nitrogen/methane). Although scientists had predicted previously that Europa might have gaseous oxygen, a definitive detection had to wait for the ultraviolet sensitivity provided by HST's Goddard High Resolution Spectrograph (GHRS) instrument. The GHRS recorded the spectral signature of molecular oxygen (O2) on Europa in ultraviolet light during observations made on June 2, 1994, over a period of six Hubble orbits. Europa was at a distance of 425 million miles (684 million kilometers) from Earth. The Hubble observations will be invaluable for scientists who are planning close-up observations of Europa as part of NASA's Galileo mission, which will arrive at Jupiter in December 1995. During its initial entry into the Jovian system on Dec. 7, Galileo will fly by Europa at a distance of less than 22,000 miles (35,000 kilometers). @START@HST Wide Field Observations of Neptune PRESS RELEASE: CONTACT: Dr. David Crisp Jet Propulsion Laboratory, MS 169-237 4800 Oak Grove Drive Pasadena, CA 91109 (818) 354-2224 dc@crispy.jpl.nasa.gov or Dr. Heidi B. Hammel Earth Atmosphere and Planetary Science Dept. Massachusetts Institute of Technology, Rm 54416 Cambridge, MA (617) 253-7568 hbh@zilla.mit.edu HUBBLE SPACE TELESCOPE WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS OF NEPTUNE Two groups have recently used the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC 2) to acquire new high-resolution images of the planet Neptune. Members of the WFPC-2 Science Team, lead by John Trauger, acquired the first series of images on 27 through 29 June 1994. These were the highest resolution images of Neptune taken since the Voyager-2 flyby in August of 1989. A more comprehensive program is currently being conducted by Heidi Hammel and Wes Lockwood. These two sets of observations are providing a wealth of new information about the structure, composition, and meteorology of this distant planet's atmosphere. Neptune is currently the most distant planet from the sun, with an orbital radius of 4.5 billion kilometers (2.8 billion miles, or 30 Astronomical Units). Even though its diameter is about four times that of the Earth (49,420 vs. 12,742 km), ground-based telescopes reveal a tiny blue disk that subtends less than 1/1200 of a degree (2.3 arc-seconds). Neptune has therefore been a particularly challenging object to study from the ground because its disk is badly blurred by the Earth's atmosphere. In spite of this, ground-based astronomers had learned a great deal about this planet since its position was first predicted by John C. Adams and Urbain Leverrier in 1845. For example, they had determined that Neptune was composed primarily of hydrogen and helium gas, and that its blue color caused by the presence of trace amounts of the gas methane, which absorbs red light. They had also detected bright cloud features whose brightness changed with time, and tracked these clouds to infer a rotation period between 17 and 22 hours. When the Voyager-2 spacecraft flew past the Neptune in 1989, its instruments revealed a surprising array of meteorological phenomena, including strong winds, bright, high-altitude clouds, and two large dark spots attributed to long-lived giant storm systems. These bright clouds and dark spots were tracked as they moved across the planet's disk, revealing wind speeds as large as 325 meters per second (730 miles per hour). The largest of the giant, dark storm systems, called the "Great Dark Spot", received special attention because it resembled Jupiter's Great Red Spot, a storm that has persisted for more than three centuries. The lifetime of Neptune's Great Dark Spot could not be determined from the Voyager data alone, however, because the encounter was too brief. Its evolution was impossible to monitor with ground-based telescopes, because it could not be resolved on Neptune's tiny disk, and its contribution to the disk-integrated brightness of Neptune confused by the presence of a rapidly-varying bright cloud feature, called the "Bright Companion" that usually accompanied the Great Dark spot. The repaired Hubble Space Telescope provides new opportunities to monitor these and other phenomena in the atmosphere of the most distant planet. Images taken with WFPC-2's Planetary Camera (PC) can resolve Neptune's disk as well as most ground-based telescopes can resolve the disk of Jupiter. The spatial resolution of the HST WFPC-2 images is not as high as that obtained by the Voyager-2 Narrow-Angle Camera during that spacecraft's closest approach to Neptune, but they have a number of other assets that enhance their scientific value, including improved ultra-violet and infrared sensitivity, better signal-to-noise, and, and greater photometric accuracy. The images of Neptune acquired by the WFPC-2 Science team in late June clearly demonstrate these capabilities. The side of the planet facing the Earth at the start of the program (11:36 Universal Time on July 27) was imaged in color filters spanning the ultraviolet (255 and 300-nm), visible (467, 588, 620, and 673- nm), and near-infrared (890-nm) parts of the spectrum. The planet then rotated 180 degrees in longitude, and the opposite hemisphere was imaged in a subset of these colors (300, 467, 588, 620, and 673-nm). The HST/WFPC-2 program more recently conducted by Hammel and Lockwood provides better longitude coverage, and a wider range of observing times, but uses a more restricted set of colors. The ultraviolet pictures show an almost featureless disk that is slightly darker near the edge. The observed contrast increases in the blue, green, red, and near-infrared images, which reveal many of the features seen by Voyager 2, including the dark band near 60 S latitude and several distinct bright cloud features. The bright cloud features are most obvious in the red and infrared parts of the spectrum where methane gas absorbs most strongly (619 and 890 nm). These bright clouds thought to be high above the main cloud deck, and above much of the absorbing methane gas. The edge of the planet's disk also appears somewhat bright in these colors, indicating the presence of a ubiquitous, high-altitude haze layer. The northern hemisphere is occupied by a single prominent cloud band centered near 30 N latitude. This planet-encircling feature may be the same bright cloud discovered last fall by ground-based observers. Northern hemisphere clouds were much less obvious at the time of the Voyager-2 encounter. The tropics are about 20 % darker than the disk average in the 890-nm images, and one of these images reveals a discrete bright cloud on the equator, near the edge of the disk. The southern hemisphere includes two broken bright bands. The largest and brightest is centered at 30 S latitude, and extends for least 40 degrees of longitude, like the Bright Companion to the Great Dark Spot. There is also a thin cloud band at 45 S latitude, which almost encircles the planet. One feature that is conspicuous by its absence is the storm system known as the Great Dark Spot. The second smaller dark spot, DS2, that was seen during the Voyager-2 encounter was also missing. The absence of these dark spots was one of the biggest surprises of this program. The WFPC-2 Science team initially assumed that the two storm systems might be near the edge of the planet's disk, where they would not be particularly obvious. An analysis of their longitude coverage revealed that less than 20 degrees of longitude had been missed in the colors where these spots had their greatest contrast (467 and 588 nm). The Great Dark Spot covered almost 40 degrees of longitude at the time of the Voyager-2 fly-by. Even if it were on the edge of the disk, it would appear as a "bite" out of the limb. Because no such feature was detected, we concluded that these features had vanished. This conclusion was reinforced by the more recent observations by Hammel and Lockwood, which also show no evidence of discrete dark spots. These dramatic changes in the large-scale storm systems and planet-encircling clouds bands on Neptune are not yet completely understood, but they emphasize the dynamic nature of this planet's atmosphere, and the need for further monitoring. Additional HST WFPC-2 observations are planned for next summer. These two teams are continuing their analysis of these data sets to place improved constraints on these and other phenomena in Neptune's atmosphere. @START@Hubble Identifies Huge Clouds of Intergalactic Gas FOR RELEASE: Immediately CONTACT: Ray Villard, (410) 338-4514 Space Telescope Science Institute Lori Stiles, (602) 621-1877 University of Arizona, News Services PRESS RELEASE NO.: STScI-PR95-05 HUBBLE IDENTIFIES HUGE CLOUDS OF INTERGALACTIC GAS Astronomers using NASA's Hubble Space Telescope have discovered evidence that clouds of hydrogen found between galaxies at distances of billions of light-years from Earth are at least ten times larger than previously thought -- at least one million light-years in diameter -- and may have a remarkable sheet-like structure. Theorists will have to rethink explanations of how such large clouds exist, according to astronomers. The new Hubble results shed light on the properties of these mysterious clouds, the true nature of which remains elusive more than 25 years after their discovery. Understanding this intergalactic material might give important clues to the nature of dark matter and processes occurring in the early universe, including galaxy formation. The observations were conducted by Nadine Dinshaw, a graduate student at the University of Arizona Steward Observatory, Craig Foltz of the University of Arizona/Smithsonian Institution Multiple Mirror Telescope Observatory, Christopher Impey of the University of Arizona Steward Observatory, Ray Weymann of the Observatories of the Carnegie Institutions of Washington, and Simon Morris of the Dominion Astronomical Observatory, Victoria, British Columbia. The intergalactic gas clouds are so diffuse they cannot be observed directly. The only signatures of their existence are the imprints they leave on the light from more distant background objects. Astronomers have used these signatures to detect the presence of the clouds and to measure some of their physical properties, but have been unable to discover information on cloud sizes and shapes. "This information is crucial to any attempt to distinguish between the several theoretical explanations for the sites and mechanisms which produce the clouds," says Craig Foltz of the University of Arizona, Tucson, a member of the Hubble team who made the discovery. Previous explanations have been that the clouds are the halos of primordial clumps of dark matter that they are the very outer halos of normal galaxies, or that they are produced by shock waves resulting from explosive galaxy formation. "These Hubble results do not explain the details of how the clouds are produced, but they directly imply that the clouds are so large that none of the popular scenarios provides an entirely adequate explanation," Foltz says. The team used Hubble's Faint Object Spectrograph at ultraviolet wavelengths to observe a pair of quasars -- extremely luminous and distant objects -- separated by an angle on the sky about one-twentieth the diameter of the full Moon. The clouds are detected by the dark absorption lines that they produce in the spectra of the light from the quasars. The quasars act like two flashlights seen from a distance of five billion to 10 billion light-years, shining through an intergalactic "forest" where the "trees" are the clouds. A problem with such studies in the past has been in finding two quasars that are appropriately paired in the sky, roughly equidistant from the Earth and about equal in brightness. The team used the HST to study a pair of quasars bright at ultraviolet wavelengths but unsuitable for ground-based observations, since ultraviolet observations are impossible to make from Earth. In the HST observations, several matching absorption lines were seen in the spectra of both quasars, implying that the clouds are at least large enough to cover the lines of sight to both quasars, or at least a million light-years in diameter, roughly ten times larger than previously thought. (By comparison, the luminous disk of our Milky Way Galaxy is about 100,000 light-years in diameter.) Detailed analysis of the observations allowed the team to estimate that the actual size of the clouds may be as much as twice as large, or two million light-years in diameter, and that they may take the form of huge filaments, sheets or flattened disks of material. "These results were absolutely unexpected," Dinshaw says of the discovery. "We were just hoping to get upper limits on the size of these clouds. We never expected to see so many matches in the absorption lines (in the spectra of each of the quasars in the pair). We never expected the sizes of these clouds would be so large." The team plans to confirm their discovery with more Hubble observations of this pair of quasars as well as other close pairs of quasars. They also have undertaken an extensive ground-based observing program to attempt to better understand both the properties of the clouds and their relationship to normal galaxies. Their results appear in the January 19, 1995 issue of the science journal Nature. @START@Surprising Hubble Images Challenge Quasar Theory EMBARGOED UNTIL 3:30 p.m. MST, January 11, 1995 SURPRISING HUBBLE IMAGES CHALLENGE QUASAR THEORY Astronomers report today that new observations from NASA's Hubble Space Telescope challenge thirty years of scientific theory about quasars, the most energetic objects in the universe. Hubble images show, to the surprise of researchers, that the environment surrounding quasars is far more violent and complex than expected, with evidence for galactic collisions and mergers. "This is a giant leap backwards in our understanding of quasars," says Professor John Bahcall of the Institute of Advanced Study at Princeton. Since their discovery in 1963, quasars (quasi-stellar objects) have been enigmatic because they emit prodigious amounts of energy from a very compact source. The most widely accepted model is that a quasar is powered by a supermassive black hole in the core of a more or less normal galaxy. However, confirming this model has been difficult because a quasar is so bright it drow ns out the light from the stars in the suspected host galaxy. Using the Wide Field Planetary Camera-2, Bahcall observed fourteen of the brightest and nearest quasars , assuming that the Space Telescope's resolution and sensitivity would at last reveal the host galaxies suggested by previous ground-based observations. "We were astonished when images of eight quasars did not reveal the bright host galaxies, as we expected based on simulations," says Bahcall, who conducted the observations with Donald Schneider, Pennsylvania State University, and Sofia Kirhakos, also of the Institute for Advanced Study. However, moderately bright host galaxies were identified in three other quasars observed. Donald Schneider emphasizes: "We are struggling to understand how our images fit into the general picture of quasar creation and evolution. This is the most enigmatic data I have ever analyzed, and it is much too early to know what the final conclusions will be." Even more puzzling, Hubble image s reveal that these apparently naked quasars have distinct companion galaxies that are so close that they will merge with the quasars in no more than ten million years. One pair in particular Bahcall calls the "smoking gun" because it reveals a galaxy that has been distorted by the gravitational pull of the quasar. Bahcall concludes, "this is clear evidence for interactions between this quasar and its nearby companion galaxy." This would mean that the quasars seen with a host galaxy have be en caught in the act of merging with their companion. Bahcall and his colleagues plan to extend his survey to other quasars. Their observations to date provide a new challenge for theorists since no current models predict the complex quasar interaction unveiled by Hubble. The results are being reported at the 185th meeting of the American Astronomical Society in Tucson, Arizona. @START@Red Dwarf Dynamo Raises Puzzles CONTACT: Ray Villard/STScI EMBARGOED UNTIL: 3:00 P.M. MST 410-338-4514 January 10, 1995 Dr. Jeffrey Linsky/JILA PRESS RELEASE NO.: STScI-PR95-03 303-492-7838 RED DWARF DYNAMO RAISES PUZZLE OVER INTERIORS OF LOWEST-MASS STARS NASA's Hubble Space Telescope has uncovered surprising evidence that powerful magnetic fields might exist around the lowest mass stars in the universe, which are near the threshold of stellar burning processes. "New theories will have to be developed to explain how these strong fields are produced, since conventional models predict that these low mass red dwarfs should have very weak or no magnetic fields," says Dr. Jeffrey Linsky of the Joint Institute for Laboratory Astrophysics (JILA) in Boulder, Colorado. "The Hubble observations provide clear evidence that very low mass red dwarf stars must have some form of dynamo to amplify their magnetic fields." His conclusions are based upon Hubble's detection of a high-temperature outburst, called a flare, on the surface of the extremely small, cool red dwarf star Van Biesbroeck 10 (VB10) also known as Gliese 752B. Stellar flares are caused by intense, twisted magnetic fields that accelerate and contain gasses which are much hotter than a star's surface. Explosive flares are common on the Sun and expected for stars that have internal structures similar to our Sun's. Stars as small as VB10 are predicted to have a simpler internal structure than that of the Sun and so are not expected to generate the electric currents required for magnetic fields that drive flares. Besides leading to a clearer understanding of the interior structure of the smallest red dwarf stars known, these unexpected results might possibly shed light on brown dwarf stars. A brown dwarf is a long-sought class of astronomical object that is too small to shine like a star through nuclear fusion processes, but is too large to be considered a planet. "Since VB10 is nearly a brown dwarf, it is likely brown dwarfs also have strong magnetic fields," says Linsky. "Additional Hubble searches for flares are needed to confirm this prediction." A QUARTER-MILLION DEGREE TORCH The star VB10 and its companion star Gliese 752A make up a binary system located 19 light-years away in the constellation Aquila. Gliese 752A is a red dwarf that is one-third the mass of the Sun and slightly more than half its diameter. By contrast, VB10 is physically smaller than the planet Jupiter and only about nine percent the mass of our Sun. This very faint star is near the threshold of the lowest possible mass for a true star (.08 solar masses), below which nuclear fusion processes cannot take place according to current models. A team led by Linsky used Hubble's Goddard High Resolution Spectrograph (GHRS) to make a one-hour long exposure of VB10 on October 12, 1994. No detectable ultraviolet emission was seen until the last five minutes, when bright emission was detected in a flare. Though the star's normal surface temperature is 4,500 degrees Fahrenheit, Hubble's GHRS detected a sudden burst of 270,000 degrees Fahrenheit in the star's outer atmosphere. Linsky attributes this rapid heating to the presence of an intense, but unstable, magnetic field. THE INTERIOR WORKINGS OF A STELLAR DYNAMO Before the Hubble observation, astronomers thought magnetic fields in stars required the same dynamo process which creates magnetic fields on the Sun. In the classic solar model, heat generated by nuclear fusion reactions at the star's center escapes through a radiative zone just outside the core. The heat travels from the radiative core to the star's surface through a convection zone. In this region, heat bubbles to the surface by motions similar to boiling in a pot of water. Dynamos, which accelerate electrons to create magnetic forces, operate when the interior of a star rotates faster than the surface. Recent studies of the Sun indicate its convective zone rotates at nearly the same rate at all depths. This means the solar dynamo must operate in the more rapidly rotating radiative core just below the convective zone. The puzzle is that stars below 20 percent the mass of our Sun do not have radiative cores, but instead transport heat from their core through convection only. The new Hubble observations suggest a magnetic dynamo perhaps of a new type can operate inside these stars. These results are being reported at the 185th meeting of the American Astronomical Society in Tucson, Arizona. @START@Hubble Finds One of the Smallest Stars in the Universe PHOTO RELEASE NO.: STScI-PRC94-54 RELEASE DATE: DECEMBER 21, 1994 HUBBLE FINDS ONE OF THE SMALLEST STARS IN THE UNIVERSE This NASA Hubble Space Telescope picture resolves, for the first time, one of the smallest stars in our Milky Way Galaxy. Called Gliese 623b or Gl623b, the diminutive star (right of center) is ten times less massive than the Sun and 60,000 times fainter. (If it were as far away as the Sun, it would be only eight times brighter than the full Moon). Located 25 light-years away in the constellation Hercules, Gl623b is the smaller component of a double star system, where the separation between the two members is only twice the distance between Earth and the Sun (approximately 200 million miles). The small star completes one orbit about its larger companion every four years. Gl623b was first detected, indirectly, from astrometric observations that measured the wobble of the primary star due to the gravitational pull of its smaller, unseen companion. However, the star is too dim and too close to its companion star to be seen by ground-based telescopes. Hubble s view is sharp enough to separate the small star from its companion. The new Hubble observations will allow astronomers to measure the intrinsic brightness and mass of Gl623b. This will lead to a better understanding of the formation and evolution of the smallest stars currently known. Red dwarf stars were once thought to be the most abundant stars in the Milky Way, and thus possibly a solution to the mystery of the Galaxy's "dark matter." However, recent Hubble observations show that these low mass stars are surprisingly rare. The image was taken in visible light on June 11, 1994, with the European Space Agency s Faint Object Camera. Credit: C. Barbieri (Univ. of Padua), and NASA/ESA Investigators: Cesare Barbieri, Gabriele Corrain, Roberto Ragazzoni (Univ. of Padua), Antonella Nota, Guido De Marchi, and Duccio Macchetto (ESA/STScI), and the FOC Instrument Definition Team. @START@Hubble Observes a New Saturn Storm PHOTO RELEASE NO.: STScI-PRC94-53 RELEASE DATE: DECEMBER 21, 1994 HUBBLE OBSERVES A NEW SATURN STORM This NASA Hubble Space Telescope image of the ringed planet Saturn shows a rare storm that appears as a white arrowhead-shaped feature near the planet's equator. The storm is generated by an upwelling of warmer air, similar to a terrestrial thunderhead. The east-west extent of this storm is equal to the diameter of the Earth (about 7,900 miles). Hubble provides new details about the effects of Saturn's prevailing winds on the storm. The new image shows that the storm's motion and size have changed little since its discovery in September, 1994. The storm was imaged with Hubble's Wide Field Planetary Camera 2 (WFPC2) in the wide field mode on December 1, 1994, when Saturn was 904 million miles from the Earth. The picture is a composite of images taken through different color filters within a 6 minute interval to create a "true-color" rendition of the planet. The blue fringe on the right limb of the planet is an artifact of image processing used to compensate for the rotation of the planet between exposures. The Hubble images are sharp enough to reveal that Saturn's prevailing winds shape a dark "wedge" that eats into the western (left) side of the bright central cloud. The planet's strongest eastward winds (clocked at 1,000 miles per hour from analysis of Voyager spacecraft images taken in 1980-81) are at the latitude of the wedge. To the north of this arrowhead-shaped feature, the winds decrease so that the storm center is moving eastward relative to the local flow. The clouds expanding north of the storm are swept westward by the winds at higher latitudes. The strong winds near the latitude of the dark wedge blow over the northern part of the storm, creating a secondary disturbance that generates the faint white clouds to the east (right) of the storm center. The storm's white clouds are ammonia ice crystals that form when an upward flow of warmer gases shoves its way through Saturn's frigid cloud tops. This current storm is larger than the white clouds associated with minor storms that have been reported more frequently as bright cloud features. Hubble observed a similar, though larger, storm in September 1990, which was one of three major Saturn storms seen over the past two centuries. Although these events were separated by about 57 years (approximately 2 Saturnian years) there is yet no explanation why they apparently follow a cycle -- occurring when it is summer in Saturn's northern hemisphere. Credit: Reta Beebe (New Mexico State University), D. Gilmore, L. Bergeron (STScI), and NASA @START@Hubble Identifies Primeval Galaxies CONTACT: Ray Villard, STScI EMBARGOED UNTIL: 1:00 PM (EST) (410) 338-4514 Tuesday, December 6, 1994 Duccio Macchetto, STScI PRESS RELEASE NO.: STScI-PR94-52 (410) 338-4790 Alan Dressler, Carnegie Institutions of Washington (818) 304-0245 Mark Dickinson, STScI (410) 338-4992 HUBBLE IDENTIFIES PRIMEVAL GALAXIES, UNCOVERS NEW CLUES TO THE UNIVERSE'S EVOLUTION Astronomers using NASA's Hubble Space Telescope as a "time machine" have obtained the clearest views yet of distant galaxies that existed when the universe was a fraction of its current age. A series of remarkable pictures, spanning the life history of the cosmos, are providing the first clues to the life history of galaxies. The Hubble results suggest that elliptical galaxies developed remarkably quickly into their present shapes. However, spiral galaxies that existed in large clusters evolved over a much longer period -- the majority being built and then torn apart by dynamic processes in a restless universe. Astronomers, surprised and enthusiastic about these preliminary findings, anticipate that Hubble's observations will lead to a better understanding of the origin, evolution, and eventual fate of the universe. The Hubble observations challenge those estimates for the age of the universe that do not allow enough time for the galaxies to form and evolve to the maturity seen at an early epoch by Space Telescope. "These unexpected results are likely to have a large influence on our cosmological models and theories of galaxy formation," says Duccio Macchetto of the European Space Agency and the Space Telescope Science Institute (STScI). "These Hubble telescope images are sufficient to provide a first determination of the properties of these very young and distant galaxies." "This is compelling, direct visual evidence that the universe is truly changing as it ages, as the Big Bang model insists," emphasizes Alan Dressler of the Carnegie Institutions, Washington, D.C. "Though much of the quantitative work can be done best with large Earth-bound telescopes, Hubble Space Telescope is providing our first view of the actual forms and shapes of galaxies when they were young." "These initial results are surprising," adds Mauro Giavalisco (STScI). "Hubble is giving us, for the first time, a chance to study in great detail the properties of very young galaxies and understand the mechanisms of their formation." A series of long exposures, taken by separate teams led by Macchetto, Dressler, and Mark Dickinson (STScI) trace galaxy evolution in rich clusters that existed when the universe was approximately one-tenth, one-third, and two-thirds its present age. Their key findings: Scientists identified the long-sought population of primeval galaxies that began to form less than one billion years after the Big Bang. One of the deepest images ever taken of the universe reveals a cosmic zoo" of bizarre fragmentary objects in a remote cluster that are the likely ancestors of our Milky Way Galaxy. A series of pictures, showing galaxies at different epochs, offers the most direct evidence to date for dynamic galaxy evolution driven by explosive bursts of star formation, galaxy collisions, and other interactions, which ultimately created and then destroyed many spiral galaxies that inhabited rich clusters. Postcards from Edge of Space and Time The researchers used Hubble as a powerful "time machine" for probing the dim past. The astronomical equivalent of digging through geologic strata on Earth, Hubble peers across a large volume of the observable universe and resolves thousands of galaxies from five to twelve billion light-years away. Because their light has taken billions of years to cross the expanding universe, these distant galaxies are fossil evidence," encoded in starlight, of events that happened long ago. These long-exposure Hubble images will help test and verify ideas about galaxy evolution based on several decades of conjecture, theoretical modeling, and ground-based observation. Ground-based observations have not been able to establish which of several competing theories best describe how galaxies formed and evolved in the early universe. Though the largest ground-based telescopes can detect objects at great distances, only Hubble can reveal the shapes of these remote objects by resolving structures a fraction of the size of our Milky Way Galaxy. This is allowing astronomers, for the first time, to discriminate among various types of distant galaxies and trace their evolution. Like watching individual frames of a motion picture, the Hubble pictures reveal the emergence of structure in the infant universe, and the subsequent dynamic stages of galaxy evolution. Now that Hubble has clearly shown that it is an exquisite time machine for seeking our cosmic "roots," astronomers are anxious to push back the frontiers of time and space even further. "Our goal now is to look back further than twelve billion years to see what we are sure will be even more dramatic evidence of galaxies in formation," says Dressler. @START@Nearby Spiral Galaxy Hidden Behind the Milky Way CONTACT: Ray Villard, STScI (410) 338-4514 Dr. Harry Ferguson, STScI (410) 338-5098 EMBARGOED UNTIL: 6:00 P.M. EST Wednesday, November 3, 1994 PRESS RELEASE NO.: STScI-PR94-51 ASTRONOMERS DISCOVER NEARBY SPIRAL GALAXY HIDDEN BEHIND THE MILKY WAY An international team of astronomers has uncovered a galaxy in our own cosmic back yard. Though only ten million light-years away (or five times the distance of the Andromeda galaxy - closest assemblage of stars to our Milky Way Galaxy), this newly discovered city of more than 100 billion stars has gone undetected previously because it is hidden from view behind our Milky Way galaxy. Called "Dwingeloo 1," after the radio telescope that first detected it, the galaxy probably belongs to a nearby group of galaxies that include two named Maffei 1 and 2. The astronomers report that its gravitational pull is likely to affect the motion of the Milky Way and the other galaxies comprising our Local Group. Located in the circumpolar constellation Cassiopeia, which lies along the Milky Way, "Dwingeloo 1" is behind a region of the sky containing a great deal of gas and dust that cut off light from objects beyond our galaxy (at an apparent brightness, or magnitude, of +14.8 , the galaxy is more than 100-times fainter than it would be if the galaxy were unobscured). The new galaxy was initially detected in radio light that penetrates this obscuring dust, and then ground-based telescopes were used to observe directly the galaxy with its distinctive barred-spiral shape, as seen through a crowded field of foreground stars belonging to the Milky Way. "For a long time, astronomers did not realize the importance of interstellar dust in shaping our view of the universe, and simply ignored parts of the sky close to the plane of the Milky Way when it came to studying extragalactic objects," says Dr. Harry Ferguson of the Space Telescope Science Institute, Baltimore, MD. "It is sobering to realize that a galaxy as close as Dwingeloo 1 could have remained hidden until now, and could have a real impact on our understanding of the motion of the Milky Way through the cosmos." The discovery team included Ferguson, Dr. Renee Kraan-Korteweg (University of Groningen), Andy Loan (a research student), Dr. Ofer Lahav and Professor Donald Lynden-Bell of the University of Cambridge; Professor Butler Burton (Leiden University); and Dr. Patricia Henning (University of New Mexico, USA). The galaxy's identification is a result of a long term project called the Dwingeloo Obscured Galaxy Survey (DOGS), which uses the 25-meter radio telescope at Dwingeloo in the Netherlands to look for radio emissions from galaxies that might be hidden from the view of optical telescopes by the Milky Way. On August 4, 1994, this "blind search" identified a radio "signature," that is characteristic of a spiral galaxy (the radio "image" is about half the apparent size of the full Moon). Within days, the discovery team contacted colleagues who observed the galaxy at visible and infrared wavelengths with telescopes on La Palma (Canary Islands), in Hawaii, and in Israel. These observations confirmed that the galaxy is a barred-spiral. The astronomers expect to find more galaxies behind the Milky Way as work on the survey continues. The results are being reported in the November 3 issue of Nature Magazine. @START@HST Measures Distance to the Most Remote Galaxy Yet CONTACT: Ray Villard, STScI EMBARGOED UNTIL: 2:00 P.M. EDT (410) 338-4514 Wednesday, October 26, 1994 Dr. Wendy L. Freedman PRESS RELEASE NO.: STScI-PR94-49 Carnegie Observatories (818) 304-0204 HUBBLE SPACE TELESCOPE MEASURES PRECISE DISTANCE TO THE MOST REMOTE GALAXY YET An international team of astronomers using NASA's Hubble Space Telescope announced today the most accurate measurement yet of the distance of the remote galaxy M100, located in the Virgo cluster of galaxies. This measurement will help provide a precise calculation of the expansion rate of the universe, called the Hubble Constant, which is crucial to determining the age and size of the universe. "Although this is only the first step in a major systematic program to measure accurately the scale, size, and age of the universe," noted Dr. Wendy L. Freedman, of the Observatories of the Carnegie Institution of Washington, "a firm distance to the Virgo cluster is a critical milestone for the extragalactic distance scale, and it has major implications for the Hubble Constant." HST's detection of Cepheid variable stars in the spiral galaxy M100, a member of the Virgo cluster, establishes the distance to the cluster as 56 million light-years (with an uncertainty of +/- 6 million light-years). M100 is now the most distant galaxy in which Cepheid variables have been measured accurately. The precise measurement of this distance allows astronomers to calculate that the universe is expanding at the rate of 80 km/sec per megaparsec (+/- 17 km/sec). For example, a galaxy one million light-years away will appear to be moving away from us at approximately 60,000 miles per hour. If it is twice that distance, it will be seen to be moving at twice the speed, and so on. This rate of expansion is the Hubble Constant. These results are being published in the October 27 issue of the journal Nature. The team of astronomers is jointly led by Freedman, Dr. Robert Kennicutt (Steward Observatory, University of Arizona), and Dr. Jeremy Mould (Mount Stromlo and Siding Spring Observatories, Australian National University). Dr. Mould noted, "Those who pioneered the development of the Hubble Space Telescope in the 1960s and 1970s recognized its unique potential for finding the value of the Hubble Constant. Their foresight has been rewarded by the marvelous data that we have obtained for M100." Using Hubble's Wide-Field and Planetary Camera (WFPC2), the team of astronomers repeatedly imaged a field where much star formation recently had taken place, and was, therefore, expected to be rich in Cepheids -- a class of pulsating stars used for determining distances. Twelve one-hour exposures, strategically placed in a two-month observing window, resulted in the discovery of 20 Cepheids. About 40,000 stars were measured in the search for these rare, but bright, variables. Once the periods and intrinsic brightness of these stars were established from the careful measurement of their pulsation rates, the researchers calculated a distance of 56 million light-years to the galaxy. (The team allowed for the dimming effects of distance as well as that due to dust and gas between Earth and M100.) Many complementary projects are currently being carried out from the ground with the goal of providing values for the Hubble Constant. However, they are subject to many uncertainties which HST was designed and built to circumvent. For example, a team of astronomers using the Canada-France-Hawaii telescope at Mauna Kea recently have arrived at a distance to another galaxy in Virgo that is similar to that found for M100 using HST -- but their result is tentative because it is based on only three Cepheids in crowded star fields. "Only Space Telescope can make these types of observations routinely," Freedman explained. "Typically, Cepheids are too faint and the resolution too poor, as seen from ground-based telescopes, to detect Cepheids clearly in a crowded region of a distant galaxy." Although M100 is now the most distant galaxy in which Cepheid variables have been discovered, the Hubble team emphasized that the HST project must link into even more distant galaxies before a definitive number can be agreed on for the age and size of the universe. This is because the galaxies around the Virgo Cluster are perturbed by the large mass concentration of galaxies near the cluster. This influences their rate of expansion. REFINING THE HUBBLE CONSTANT These first HST results are a critical step in converging on the true value of the Hubble Constant, first developed by the American astronomer Edwin Hubble in 1929. Hubble found that the farther a galaxy is, the faster it is receding away from us. This "uniform expansion" effect is strong evidence the universe began in an event called the "Big Bang" and that it has been expanding ever since. To calculate accurately the Hubble Constant, astronomers must have two key numbers: the recession velocities of galaxies and their distances as estimated by one or more cosmic "mileposts," such as Cepheids. The age of the universe can be estimated from the value of the Hubble Constant, but it is only as reliable as the accuracy of the distance measurements. The Hubble constant is only one of several key numbers needed to estimate the universe's age. For example, the age also depends on the average density of matter in the universe, though to a lesser extent. A simple interpretation of the large value of the Hubble Constant, as calculated from HST observations, implies an age of about 12 billion years for a low-density universe, and 8 billion years for a high-density universe. However, either value highlights a long-standing dilemma. These age estimates for the universe are shorter than the estimated ages of some of the oldest stars found in the Milky Way and in globular star clusters orbiting our Milky Way. Furthermore, small age values pose problems for current theories about the formation and development of the observed large-scale structure of the universe. COSMIC MILEPOSTS Cepheid variable stars rhythmically change in brightness over intervals of days (the prototype is the fourth brightest star in the circumpolar constellation Cepheus). For more than half a century, from the early work of the renowned astronomers Edwin Hubble, Henrietta Leavitt, Allan Sandage, and Walter Baade, it has been known that there is a direct link between a Cepheid's pulsation rate and its intrinsic brightness. Once a star's true brightness is known, its distance is a relatively straightforward calculation because the apparent intensity of light drops off at a geometrically predictable rate with distance. Although Cepheids are rare, once found, they provide a very reliable "standard candle" for estimating intergalactic distances, according to astronomers. Besides being an ideal hunting ground for the Cepheids, M100 also contains other distance indicators that can in turn be calibrated with the Cepheid result. This majestic, face-on, spiral galaxy has been host to several supernovae, which are also excellent distance indicators. Individual supernovae (called Type II, massive exploding stars) can be seen to great distances, and, so, can be used to extend the cosmic distance scale well beyond Virgo. As a crosscheck on the HST results, the distance to M100 has been estimated using the Tully-Fisher relation (a means of estimating distances to spiral galaxies using the maximum rate of rotation to predict the intrinsic brightness) and this independent measurement also agrees with both the Cepheid and supernova "yardsticks." HST Key Projects are scientific programs that have been widely recognized as being of the highest priority for the Hubble Space Telescope and have been designated to receive a substantial amount of observing time on the telescope. The Extragalactic Distance Scale Key Project involves discovering Cepheids in a variety of important calibrating galaxies to determine their individual distances. These distances then will be used to establish an accurate value of the Hubble Constant. @START@Hubble Observations Shed New Light on Jupiter Collision CONTACT: Ray Villard, STScI FOR RELEASE: September 29,1994 (410) 338-4514 PRESS RELEASE NO.: STScI-PR94-48 HUBBLE OBSERVATIONS SHED NEW LIGHT ON JUPITER COLLISION In the weeks following comet P/Shoemaker-Levy 9's spectacular July collision with Jupiter, a team of Hubble Space Telescope astronomers has pored over imaging and spectroscopic data gleaned during the interplanetary bombardment. Their initial findings, combined with results from other space-borne and ground-based telescopes, shed new light on Jupiter's atmospheric winds, it's immense magnetic field, the mysterious dark debris from the impacts, and the composition of the doomed comet itself. These early results are being presented at a press conference today at NASA Headquarters in Washington D.C. by astronomers John Clarke (University of Michigan, Ann Arbor MI), Heidi Hammel (MIT), and Harold Weaver and Melissa McGrath (Space Telescope Science Institute, Baltimore, MD). THE LAST DAYS OF THE COMET Before the comet impact, there was a great deal of speculation and prediction about whether the 21 nuclei would survive before reaching Jupiter, or were so fragile that gravitational forces would pull them apart into thousands of smaller fragments. Hubble helped solve this question by watching the nuclei until about 10 hours before impact. HST's high resolution images show that the nuclei, the largest of which were probably a few kilometers across, did not breakup catastrophically before plunging into Jupiter's atmosphere. This reinforces the notion that the comet's atmospheric explosions were produced by solid, massive impacting bodies. HST's resolution also showed that the nuclei were releasing dust all along the path toward Jupiter, as would be expected from a comet. This was evident in the persistence of spherical clouds of dust surrounding each nucleus throughout most of the comet's journey. About a week before impact, these dust clouds were stretched out along the path of the comet's motion by Jupiter's increasingly strong gravity. PIERCING JUPITER'S MAGNETIC FIELD About four days before impact, at a distance of 2.3 million miles from Jupiter, nucleus "G" of comet P/Shoemaker-Levy 9 apparently penetrated Jupiter's powerful magnetic field, the magnetosphere. (Jupiter's magnetosphere is so vast, if visible to the naked eye, it would be about the size of the full moon.) Hubble's Faint Object Spectrograph (FOS) recorded dramatic changes at the magnetosphere crossing that provided a rare opportunity to gather more clues on the comet's true composition. During a two minute period on July 14, HST detected strong emission from ionized magnesium (Mg II), an important component of both comet dust and asteroids. However, if the nuclei were ice-laden -- as expected of a comet nucleus -- astronomers expected to detect the hydroxyl radical (OH). The HST did not see OH, casting some doubt on the cometary nature of P/Shoemaker-Levy 9. Eighteen minutes after comet P/Shoemaker- Levy 9 displayed the flare-up in Mg II emissions, there was also a dramatic change in the light reflected from the dust particles in the comet. NEW AURORAL ACTIVITY The HST detected unusual auroral activity in Jupiter's northern hemisphere just after the impact of the comet's "K" fragment. This impact completely distrupted the radiation belts which have been stable over the last 20 years of radio observations. Aurorae, glowing gases that create the northern and southern lights, are common on Jupiter because energetic charged particles needed to excite the gases are always trapped in Jupiter's magnetosphere. However, this new feature seen by Hubble was unusual because it was temprorarily as bright or brighter than the normal aurora, short-lived, and outside the area where Jovian aurorae are normally found. Astronomers believe that the K impact created an electromagnetic disturbance that traveled along magnetic field lines into the radiation belts. This scattered charged particles, which normally exist in the radiation belts, into Jupiter's upper atmosphere. X-ray images taken with the ROSAT satellite further bolster the link to the K impact. They reveal unexpectedly bright X-ray emission, mainly from the north foot of magnetic field lines connected to the impact site, that was brightest near the time of the K impact, and then faded. SWEPT ACROSS JUPITER Observations made with HST's Wide Field Planetary Camera-2, a week and a month after impact, have been used to make global maps of Jupiter for tracking changes in the dark debris caught up in the high speed winds at Jupiter's cloudtops. This debris is a natural tracer of wind patterns and allows astronomers a better understanding of the physics of the Jovian atmosphere. The high speed easterly and westerly jets have turned the dark "blobs" originally at the impact sites into striking "curly-cue"features. Although individual impact sites are still visible a month later despite the shearing, the fading of Jupiter's scars has been substantial and it now appears that Jupiter will not suffer any permanent damage from the explosions. Hubble's ultraviolet observations show the motion of very fine impact debris particles now suspended high in Jupiter's atmosphere (before eventually diffusing down to lower altitudes). This provides the first information ever obtained about Jupiter's high altitude wind patterns. Hubble gives astronomers a "three dimensional" perspective showing that the wind patterns at high altitudes and how they differ from those at the visible cloud-top level. At lower altitudes, the impact debris follows east-west winds driven by sunlight and Jupiter's own internal heat. By contrast, winds in the high Jovian stratosphere move primarily from the poles toward the equator because they are driven mainly by auroral heating from high energy particles. WHAT IS THAT DARK STUFF MADE OF? The HST Faint Object Spectrograph (FOS) detected many gaseous absorptions associated with the impact sites and followed their evolution over the next month. Most surprising were the strong signatures from sulfur-bearing compounds like diatomic sulfur (S2), carbon disulfide (CS2), and hydrogen sulfide (H2S). Ammonia (NH3) absorption was also detected. The S2 absorptions seemed to fade on timescales of a few days, while the NH3 absorptions at first got stronger with time, and finally started fading after about one month. During observations near the limb of Jupiter, the FOS detected emissions from silicon, magnesium, and iron that could only have originated from the impacting bodies, since Jupiter itself normally does not have detectible amounts of these elements. WAS P/SHOEMAKER-LEVY 9 A COMET OR AN ASTEROID? At present, observations seem to slightly favor a cometary origin, though an asteroidal origin cannot yet be ruled out. The answer isn't easy because comets and asteroids have so much in common: they are small bodies; they are primordial, forming 4.6 billion years ago along with the planets and their satellites; either type of object can be expected to be found at Jupiter's distance. The key difference is that comets are largely icy while the asteroids are virtually devoid of ice because they formed too close to the Sun. The attached table summarizes the observational results that shed light on this question. @START@Hubble Rules Out Leading Explanation for Dark Matter CONTACT: Ray Villard, STScI EMBARGOED UNTIL: 12:00 NOON, EST (410) 338-4514 Tuesday, November 15, 1994 PRESS RELEASE NO.: STScI-PR94-41 John Bahcall, Institute for Advanced Study (609) 734-8054 Francesco Paresce, STScI (410) 338-4823 HUBBLE RULES OUT A LEADING EXPLANATION FOR DARK MATTER Two teams of astronomers, working independently with NASA's Hubble Space Telescope (HST), have ruled out the possibility that red dwarf stars constitute the invisible matter, called dark matter, believed to account for more than 90 percent of the mass of the universe. Until now, the dim, small stars were considered ideal candidates for dark matter. Whatever dark matter is, its gravitational pull ultimately will determine whether the universe will expand forever or will someday collapse. "Our results increase the mystery of the missing mass. They rule out a popular but conservative interpretation of dark matter," said Dr. John Bahcall, professor of natural science at the Institute of Advanced Study, Princeton, NJ, a leader of one of the teams. The group led by Bahcall and Andrew Gould of Ohio State University, Columbus, Ohio, (formerly of the Institute for Advanced Study) showed that faint red dwarf stars, which were thought to be abundant, actually are sparse in the Milky Way, Earth's home galaxy, and in the universe by inference. The team, led by Dr. Francesco Paresce of the Space Telescope Science Institute in Baltimore, MD, and the European Space Agency, determined that the faint red stars rarely form and that there is a cutoff point below which nature does not make this type of dim, low-mass star. The pair of HST observations involved accurately counting stars and gauging their brightness. The observations overturn several decades of conjecture, theory and observation about the typical mass and abundance of the smallest stars in the universe. PREVIOUS GROUND-BASED RESULTS INCONCLUSIVE In our own stellar neighborhood, there are almost as many red dwarfs as there are all other types of stars put together. The general trend throughout our galaxy is that small stars are more plentiful than larger stars, just as there are more pebbles on the beach than rocks. This led many astronomers to believe that they were only seeing the tip of the iceberg and that many more extremely faint red dwarf stars were at the limits of detection with ground-based instruments. According to stellar evolution theory, stars as small as eight percent of the mass of our Sun are still capable of shining by nuclear fusion processes. Over the past two decades, theoreticians have suggested that the lowest mass stars also should be the most prevalent and, so, might provide a solution for dark matter. This seemed to be supported by previous observations with ground-based telescopes that hinted at an unexpected abundance of what appeared to be red stars at the faintest detection levels achievable from the ground. However, these prior observations were uncertain because the light from these faint objects is blurred slightly by Earth's turbulent atmosphere. This makes the red stars appear indistinguishable from the far more distant, diffuse-looking galaxies. PINNING DOWN THE LONG-SOUGHT HALO POPULATION Hubble's capabilities made it possible for a team of astronomers led by Bahcall and Gould to observe red stars that are 100 times dimmer than those detectable from the ground -- a level where stars can be distinguished easily from galaxies. Hubble Space Telescope's extremely high resolution also can separate faint stars from the much more numerous galaxies by resolving the stars as distinct points of light, as opposed to the "fuzzy" extended signature of a remote galaxy. Bahcall and Gould, with their colleagues Chris Flynn and Sophia Kirhakos (also of the Institute for Advanced Study, Princeton) used images of random areas in the sky taken with the HST Wide Field Planetary Camera 2 (in WF mode) while the telescope was performing scheduled observations with other instruments. By simply counting the number of faint stars in the areas observed by HST, the scientists demonstrated that the Milky Way has relatively few faint red stars. The HST observations show that dim red stars make up no more than six percent of the mass in the halo of the Galaxy, and no more than 15 percent of the mass of the Milky Way's disk. The Galactic halo is a vast spherical region that envelopes the Milky Way's spiral disk of stars, of which Earth's Sun is one inhabitant. FAINT RED STARS MISSING FROM A GLOBULAR CLUSTER By coincidence, Paresce pursued the search for faint red dwarfs after his curiosity was piqued by an HST image taken near the core of the globular cluster NGC 6397. He was surprised to see that the inner region was so devoid of stars, he could see right through the cluster to far more distant background galaxies. Computer simulations based on models of stellar population predicted the field should be saturated with dim stars -- but it wasn't. HST's sensitivity and resolution allowed Paresce, and co-investigators Guido De Marchi (ST ScI, and the University of Firenze, Italy), and Martino Romaniello (University of Pisa, Italy) to conduct the most complete study to date of the population of the cluster (globular clusters are ancient, pristine laboratories for studying stellar evolution). To Paresce's surprise, he found that stars 1/5 the mass of our Sun are very abundant (there are about 100 stars this size for every single star the mass of our Sun) but that stars below that range are rare. "The very small stars simply don't exist, " he said. A star is born as a result of the gravitational collapse of a cloud of interstellar gas and dust. This contraction stops when the infalling gas is hot and dense enough to trigger nuclear fusion, causing the star to glow and radiate energy. "There must be a mass limit below which the material is unstable and cannot make stars," Paresce emphasizes." Apparently, nature breaks things off below this threshold." Paresce has considered the possibility that very low-mass stars formed long ago but were thrown out of the cluster due to interactions with more massive stars within the cluster, or during passage through the plane of our Galaxy. This process would presumably be common among the approximately 150 globular clusters that orbit the Milky Way. However, the ast-off stars would be expected to be found in the Milky Way's halo, and Bahcall's HST results don't support this explanation. THE SEARCH FOR DARK MATTER The HST findings are the latest contribution to a series of recent, intriguing astronomical observations that are struggling to pin down the elusive truth behind the universe's "missing mass." Models describing the origin of helium and other light elements during the birth of the universe, or "Big Bang," predict that less than 5% of the universe is made up of "normal stuff," such as neutrons and protons. This means more than 90% of the universe must be some unknown material that does not emit any radiation that can be detected by current instrumentation. Candidates for dark matter include black holes, neutron stars and a variety of exotic elementary particles. Within the past year, astronomers have uncovered indirect evidence for a dark matter candidate called a MACHO (MAssive Compact Halo Objects). These previous observations detected several instances of an invisible object that happens to lie along the line of sight to an extragalactic star. When the intervening object is briefly aligned between Earth and a distant star, it amplifies, or gravitationally lenses, the light from the distant star. The new HST finding shows that faint red stars are not abundant enough to explain the gravitational lensing events attributed to MACHOs. Bahcall cautions, however, that his results do not rule out other halo objects that could be smaller than the red stars such as brown dwarfs -- objects not massive enough to burn hydrogen and shine in visible light. Additional circumstantial evidence for dark matter in the halo of our galaxy has been inferred from its gravitational influence on the motions of stars within the Milky Way's disk. Recently, this notion was further supported by ground-based observation, made by Peggy Sachett of the Institute for Advanced Study, that show a faint glow of light around a neighboring spiral galaxy that is the shape expected for a halo composed of dark matter. This could either be light from the dark matter itself or stars that trace the presence of the galaxy's dark matter. The reality of dark matter also has been inferred from the motions of galaxies in clusters, the properties of high-temperature gas located in clusters of galaxies and from the relative amounts of light elements and isotopes produced in the Big Bang. The ultimate fate of the universe will be determined by the amount of dark matter present. Astronomers have calculated that the amount of matter - - planets, stars and galaxies -- observed in the universe cannot exert enough gravitational pull to stop the expansion which began with the Big Bang. Therefore, if the universe contains less than a critical density of matter it will continue expanding forever, but if enough of the mysterious dark matter exists, the combined gravitational pull someday will cause the universe to stop expanding and eventually collapse. Bahcall stresses, "The dark matter problem remains one of the fundamental puzzles in physics and astronomy. Our results only sharpen the question of what is the dark matter." Bahcall's results appeared in the November 1, 1994 issue of the Astrophysical Journal. Paresce's paper will appear in the February 10, 1995, issue of the Astrophysical Journal. @START@Secrets of Star Birth in the Early Universe CONTACT: Ray Villard, STScI FOR RELEASE: October 17, 1994 (410) 338-4514 PRESS RELEASE NO.: STScI-PR94-40 Dr. Nino Panagia (410) 338-4916 TALE OF TWO CLUSTERS YIELDS SECRETS OF STAR BIRTH IN THE EARLY UNIVERSE NASA's Hubble Space Telescope has provided new insights into how stars might have formed many billions of years ago in the early universe. Hubble observations of a pair of star clusters suggest they might be linked through stellar evolution processes. The pair of clusters are 166,000 light-years away in the Large Magellanic Cloud (LMC) in the southern constellation Doradus. The clusters are unusually close together for being distinct and separate objects, according to Hubble astronomers. Previously, such detailed stellar population studies were restricted to nearby star-forming regions within the plane of our Milky Way Galaxy. However, Hubble's high-quality images extend these stellar studies one hundred times farther into the universe, out to the distance of a neighboring galaxy. Because the LMC lies outside of our Milky Way Galaxy, it is a natural laboratory for studying the birth and evolution of stars. The stars in the LMC have few heavy elements and, so, their composition is more primordial -- like the stars which first formed in the early universe. A preliminary assessment of the HST observation indicates that these compact clusters contained many more massive stars than expected. "If this were also the case billions of years ago, it would have altered drastically the early history of the universe," says Dr. Nino Panagia of the Space Telescope Science Institute (STScI) in Baltimore, Maryland and the European Space Agency ESA). Panagia and R. Gilmozzi (also of STScI/ESA) and co-investigators utilized fully HST's unique capabilities -- ultraviolet sensitivity, ability to see faint stars, and high resolution -- to identify three separate populations in this concentration of nearly 10,000 stars. (Previous observations with ground-based telescopes resolved less than 1,000 stars in this region.) About 60 percent of the stars belong to the dense cluster called NGC 1850, which is estimated to be 50 million years old. A loose distribution of extremely hot massive stars in the same region are only about 4 million years old and represent about 20 percent of the stars in the image. (The remainder are field stars in the LMC.) The significant difference between the two cluster ages suggests these are two separate star groups that lie along the same line of sight. The younger, more open cluster probably lies 200 light-years beyond the older cluster, says Panagia. He emphasizes that if it were in the foreground, then dust in the younger cluster would obscure stars in the older cluster. Because having two well-defined star populations so separated by such a small gap of space is unusual, this juxtaposition suggests that they might be linked in an evolutionary sense. A possible scenario is that an expanding "bubble" of hot gas, from more than 1,000 supernova explosions in the older cluster, might have triggered the birth of the younger cluster. This would have happened when the bubble expanded across space for 45 million years before plowing into a wall of cool gas and dust. The shock front then caused the gas to contract, precipitating a new generation of star formation. The massive, hot stars are destined to explode in a few million years, and thus create yet a new expanding bubble of gas. The findings will be published in the November 1, 1994 issue of the Astrophysical Journal Letters. Co-investigators are: R. Gilmozzi (Space Telescope Science Institute, Baltimore, Maryland and ESA), E.K. Kinney (Space Telescope Science Institute, Baltimore, Maryland), S.P. Ewald (California Institute of Technology, Pasadena, California), N. Panagia (Space Telescope Science Institute, Baltimore, Maryland, ESA, and University of Catania, Italy), and M. Romaniello (University of Pisa, Italy). @START@Protoplanetary Disks Around Newborn Stars CONTACT: Ray Villard, STScI Monday, June 13, 1994 (410) 338-4514 PRESS RELEASE NO.: STScI-PR94-24 Dr. C. Robert O'Dell (713) 527-8101 x3633 HUBBLE CONFIRMS ABUNDANCE OF PROTOPLANETARY DISKS AROUND NEWBORN STARS NASA announced today that a Rice University astronomer using the Hubble Space Telescope has uncovered the strongest evidence yet that the process which may form planets is common in the Milky Way galaxy, of which Earth is a part, and the universe beyond. Dr. C. Robert O'Dell said observations with the newly repaired telescope clearly reveal that great disks of dust -- the raw material for planet formation -- are swirling around at least half and probably many more of the stars in the Orion Nebula, a region only 1,500 light-years from Earth where new stars are being born. O'Dell and a colleague, Zheng Wen, formerly of Rice and now at the University of Kentucky, surveyed 110 stars and found disks around 56 of them. Because it is easier to detect the star than the disk, it is likely that far more stars are being orbited by protoplanetary material, O'Dell said. O'Dell first discovered these disks, which he dubbed "proplyds," in Hubble Space Telescope images taken in 1992. However, the new images bolster his theory by distinguishing clearly that the objects are indeed pancake-shaped disks of dust, not shells of dust as some astronomers have maintained. HST clearly resolves a young star at the center of each disk. O'Dell has also been able to measure at least a portion of the mass of a dust disk and found that the disk contains enough material to make an earth-like planet. The theory that the Earth and other planets of the solar system were formed out of just such a disk some 4.5 billion years ago by the coalescing of matter caused by gravitational attraction is widely accepted. O'Dell said the disks in the Orion Nebula presumably contain the same materials that constitute the planets of Earth's solar system -- carbon, silicates, and other base constituents. The only confirmed planetary system to date, consists of three earth-sized bodies orbiting a neutron star 1,000 light-years away. Since the neutron star is the burned-out remnant from a stellar explosion, these planets might have formed at the end of the star's life, and so, are not a good indicator of the abundance of planetary systems like our own. O'Dell's findings of an abundance of protoplanetary disks in a cluster of young stars reinforces the assumption that planetary systems are common in the universe. And because planets are necessary for life, as it is known on Earth, to become established and flourish, the likelihood that planets are common in the universe raises the likelihood of the existence of life beyond Earth. The only place where life is known to exist is Earth. Finding life, or fossils of life, elsewhere in our solar system -- the major object of the exploration of Mars -- would be the first evidence of life beyond Earth. For life to arise independently on two planets in the same solar system would mean that life likely is not accidental and is abundant in the universe. The Hubble images clearly distinguish the central star from the disk and show that stars in Orion that are the mass of our Sun and lower are likely to possess disks. Stars hotter than our Sun might destroy the dusty disks before they can agglomerate into planets, according to O'Dell. Hubble can see the disks because they are illuminated by the hottest stars in the Orion Nebula, and some of them are seen in silhouette against the bright nebula. However, some of these proplyds are bright enough to have been seen previously by ground-based optical and radio telescopes as stars. Their true nature was not recognized until the Hubble observations. One striking HST image shows a dark elliptical disk silhouetted against the bright background of the Orion nebula. "This object represents the most direct evidence uncovered to date for protoplanetary disks," says O'Dell. Hubble's resolution has allowed O'Dell to determine accurately the mass of the outer rim of the disk. It turns out to be at least several times the mass of our Earth. The entire disk is 53 billion miles across, or 7.5 times the diameter of our solar system. The central, reddish star is about one fifth the mass of our Sun. The disks identified in the Hubble survey are a missing link in the understanding of how planets like those in our planetary system form. Their abundance in a young star cluster shows that the basic material of planets exists around a large fraction of stars. This reinforces the probability that many stars have planetary systems. Because the Orion star cluster is less than a million years of age, there has not been enough time for planets to agglomerate from the dust within the disks. Many of the stars are still contracting towards the mature status that they will then retain for billions of years. The most massive stars in the cluster have already reached their adult stage of maximum hydrogen fuel burning and their surfaces have become so hot that their radiation heats up the gas left over after star formation. This is visible to observers with binoculars as the Orion nebula, which is in the middle of the region known as the sword of Orion. THE GENESIS OF A SOLAR SYSTEM Hubble Space Telescope's detailed images confirm more than a century of speculation, conjecture, and theory about the genesis of a solar system. According to current theories, the dust contained within the disks eventually agglomerates to make planets. Hubble's images provide direct evidence that dust surrounding a newborn star has too much spin to be drawn into the collapsing star. Instead, the material spreads out into a broad, flattened disk. Before the Hubble discovery, remnant dust disks had been confirmed around only four stars: Beta Pictoris, Alpha Lyrae, Alpha Piscis Austrini, and Epsilon Eridani. They are a fraction of the mass of the proplyds in Orion, and might be leftover material from the planet formation process. Less direct detections of circumstellar material around stars in nearby star forming regions have been made by radio and infrared telescopes. Unlike these previous observations, Hubble has observed newly formed stars less than a million years old which are still contracting out of primordial gas. Planets are considered a fundamental prerequisite for the existence of life as we know it. A planet provides a storehouse of chemicals for manufacturing the complex molecules of biology, gravitationally holds an atmosphere of gasses that are used by life, and receives heat and light from the central star to power photosynthesis and other chemical reactions required by life forms. O'Dell's Orion results will appear in the November 20 issue of The Astrophysical Journal. @START@Massive Black Hole at Heart of Active Galaxy CONTACT: Ray Villard, STScI Wednesday, May 25, 1994 (410) 338-4514 PRESS RELEASE NO.: STScI-PR94-23 Dr. Holland Ford, STScI/JHU (410) 338-4803 (410) 516-8653 HUBBLE CONFIRMS EXISTENCE OF MASSIVE BLACK HOLE AT HEART OF ACTIVE GALAXY Astronomers using NASA's Hubble Space Telescope have found seemingly conclusive evidence for a massive black hole in the center of the giant elliptical galaxy M87, located 50 million light years away in the constellation Virgo. Earlier observations suggested the black hole was present, but were not decisive. This observation provides very strong support for the existence of gravitationally collapsed objects, which were predicted 80 years ago by Albert Einstein's general theory of relativity. "If it isn't a black hole, then I don't know what it is," says Dr. Holland Ford of the Space Telescope Science Institute and The Johns Hopkins University in Baltimore, Maryland. "A massive black hole is actually the conservative explanation for what we see in M87. If it's not a black hole, it must be something even harder to understand with our present theories of astrophysics," adds fellow investigator Dr. Richard Harms of the Applied Research Corp. in Landover, Maryland. The discovery is based on velocity measurements of a whirlpool of hot gas that is orbiting around the black hole in the form of a disk. The presence of the disk, discovered in recent Hubble images, allows for an unprecedented, precise measurement of the mass of the object at the hub of the disk. A black hole is an object that is so massive yet compact nothing can escape its gravitational pull, not even light. The object at the center of M87 fits that description. It weights as much as three billion suns, but is concentrated into a space no larger than our solar system. Now that astronomers have seen the signature of the tremendous gravitational field at the center of M87, it is clear that the region contains only a fraction of the number of stars that would be necessary to create such a powerful attraction. There must be something else there that cannot be seen. Ford and Harms were astounded by the M87 images taken with the telescope's Wide Field Planetary Camera-2 (in PC mode) on Feb. 27. They hadn't anticipated seeing such clear evidence of a gaseous disk in the center of M87. "It's just totally unexpected to see the spiral-like structure in the center of an elliptical galaxy," Ford says. Ford and Harms used HST's Faint Object Spectrograph to measure the speeds of orbiting gas on either side of the disk from regions located about 60 light-years from the black hole at the center. They calculated that the disk of hot (about 10,000 Kelvin), ionized gas is rotating at tremendous speeds around a central object that is extremely massive but extraordinarily compact -- a black hole. "Once you get that measurement, all you need is straightforward Newtonian physics to calculate the mass of the central object that's making the disk spin," says Harms. The measurement was made by studying how the light from the disk is blueshifted and redshifted -- as one side of the disk spins toward us and the other side spins away from us. The gas on one side of the disk is speeding away from Earth, at a speed of about 1.2 million miles per hour (550 kilometers per second). The gas on the other side of the disk is whipping around at the same speed, but in the opposite direction, as it approaches viewers on Earth. "Now, it all knits together," Ford said. "We see a disk-like structure that appears to have spiral structure, and it's rotating. One side is approaching, and the other is receding." The cloud of gas is composed mostly of hydrogen. The hydrogen atoms have been ionized, or stripped of their single electron, possibly by radiation originating near the black hole. Over the next few months, they will attempt to peer even closer to the center, where the disk should be spinning at even higher speeds, improving the measurement of the black hole's mass. M87: A NEARBY ACTIVE GALAXY Since observations as early as 1917, astronomers have suspected that unusual activity was taking place in the center of M87. They discovered a long finger of energy emanating from the nucleus. Investigations using radio telescopes in the 1950s detected large emissions of energy from the galaxy. This made it clear that the bright optical jet and radio source were the result of energy released by something in the center of the galaxy. In high resolution images, the jet appears as a string of knots (some as small as ten light-years across) within a widening cone extending out from M87's core. A massive black hole had been the suspected "engine" for generating the enormous energies that power the jet. The gravitational energy is released by gas falling into the black hole, producing a beam or jet of electrons spiraling outward at nearly the speed of light. HUNTING FOR BLACK HOLES Hubble's observation confirms more than two centuries of theory and conjecture about the reality of black holes. The term black hole was coined in 1967 by American physicist John Wheeler. However, French scientist Simone Pierre LaPlace first speculated that "dark stars" might exist, which would have such intense gravitation that light itself could not escape. This conjecture was put into a theoretical framework with Einstein's general theory of relativity, published in 1915, which postulated that very massive objects actually warp space and time. The theory was supported in 1916 when German physicist Karl Schwarzschild described the mathematical basis behind black holes. For decades, however, black holes were regarded not as real astronomical objects, but merely as mathematical curiosities. With the discovery of active galaxies and quasars, black holes have become the favored "engine" for explaining a wide array of powerful and energetic events seen in the universe. Earlier Hubble Space Telescope observations found strong circumstantial evidence for the presence of a massive black hole in the core of M87, as well and other galaxies -- both active and quiescent. These observations show a rapid increase in starlight toward the center of a galaxy. This suggests that stars are concentrated around the center due to the gravitational pull of a massive black hole. However, the black hole's mass could not be determined until Hubble's spectroscopic capabilities were used to measure the actual motion of gas around the black hole. Such high spatial resolution spectroscopic observations were not possible prior to the installation of the COSTAR by the astronauts during the December 1993 First Servicing Mission. The research team included Holland Ford at the Johns Hopkins University and STScI; Richard Harms at Applied Research Corp. in Landover, Md.; and astronomers Zlatan Tsvetanov, Arthur Davidsen, and Gerard Kriss at Johns Hopkins; Ralph Bohlin and George Hartig at Space Telescope Science Institute; Linda Dressel and Ajay K. Kochhar at Applied Research Corp. in Landover, Md.; and Bruce Margon from the University of Washington in Seattle. @START@Mysterious Ring Structure Around Supernove 1987A CONTACT: Ray Villard, STScI THURSDAY, MAY 19, 1994 (410) 338-4514 PRESS RELEASE NO.: STScI-PR94-22 Dr. Christopher Burrows ESA/STScI (410) 338-4913 HUBBLE FINDS MYSTERIOUS RING STRUCTURE AROUND SUPERNOVA 1987A NASA's Hubble Space Telescope (HST) has obtained the best images yet of a mysterious mirror- imaged pair of rings of glowing gas that are encircling the site of the stellar explosion supernova 1987A. One possibility is that the two rings might be "painted" by a high-energy beam of radiation or particles, like a spinning light- show laser beam tracing circles on a screen. The source of the radiation might be a previously unknown stellar remnant that is a binary companion to the star that exploded in 1987. Images taken by Hubble show a dim object in the position of the suspected source of the celestial light show. "The Hubble images of the rings are quite spectacular and unexpected," says Dr. Chris Burrows of the European Space Agency and the Space Telescope Science Institute in Baltimore, Maryland. Burrows used Hubble's Wide Field Planetary Camera 2 to image the rings in February 1994. The striking Hubble picture actually shows three rings. The smaller "center" ring of the trio was seen previously. The larger pair of outer rings were also seen in ground-based images, but the interpretation was not possible until the higher resolution Hubble observations. Though all of the rings probably are inclined to our view (so that they appear to intersect), they probably are in three different planes. The small bright ring lies in a plane containing the supernova; the two rings lie in front and behind it. To create the beams illuminating the outer rings, the remnant would need to be a compact object such as a black hole or neutron star with a nearby companion. Material falling from the companion onto the compact object would be heated and blasted back into space along two narrow jets, along with a beam of radiation. As the compact object spins it might wobble or precess about its axis, like a child's top winding down. The twin beam would then trace out great circles like jets of water from a spinning lawn sprinkler. If the rings are caused by a jet, however, the beams are extremely narrow (collimated to within one degree). This leads Burrows to conclude: "This is an unprecedented and bizarre object. We have never seen anything behave like this before." The jet model explains why the rings appear to be mirror imaged, and why they appear to be symmetrical about a point offset from the center of the explosion. Burrows got the idea for the beam explanation when he noticed that where a ring appears brighter, an equally bright region appears on opposite ring. By connecting lines between the similar clumps on opposite rings Burrows found a common center. However, it is offset from the heart of the supernova ejecta. When Burrows did a detailed inspection of the HST image, he found a dim object which may be the source of the beam at the predicted location. The object is about 1/3 light-year from the center of the supernova explosion. >From previous HST observations and images at lower resolution taken at ground-based observatories, astronomers had expected to see an hourglass-shaped bubble being blown into space by the supernova's progenitor star. "The rings are probably on the surface of the hourglass shape," says Burrows. The hourglass was formed by a wind of slow-moving gas that was ejected by the star when it was a red supergiant, and a much faster wind of gas that followed during the subsequent blue supergiant stage. The hourglass was produced by the fact that the stellar wind from the red giant was denser in the equatorial plane of the star. When the star reached the blue supergiant stage, the faster winds tended to break out at the poles of the star. Energetic radiation from the supernova explosion illuminated the dense gaseous material in the equatorial "waist" of the hourglass, causing it to glow -- thus explaining the central bright ring. However, the two outer rings might be painted on the surface of the hourglass by a very different process, by the beams from the stellar remnant. Further observations with HST will study any further changes that might occur. In particular, if a remnant companion really exists, it should collide with the supernova's expanding cloud of ejecta in the mid 1990s. The observations were led by Dr. Chris Burrows in collaboration with the WFPC 2 Investigation Definition Team. The supernova is 169,000 light years away, and lies in the dwarf galaxy called the Large Magellanic Cloud, which can be seen from the southern hemisphere. @START@HST Observes the Supernova in the Whirlpool Galaxy CONTACT: Ray Villard, STScI Thursday, May 19, 1994 (410) 338-4514 PRESS RELEASE NO.: STScI-PR94-20 Dr. Robert P. Kirshner, Harvard University (617) 495-7519 HST OBSERVES THE SUPERNOVA IN THE WHIRLPOOL GALAXY NASA's Hubble Space Telescope has returned valuable new images of supernova 1994I in the inner regions of the "Whirlpool Galaxy," M51, located 20 million light-years away in the constellation Canes Venatici. The images were taken with the Wide Field and Planetary Camera 2 (WFPC2). The supernova was discovered by amateur astronomers on April 2, 1994 and has been the target of investigations by astronomers using ground-based optical and radio telescopes. At its brightest, around April 10, the supernova was about 100 million times brighter than the Sun. Previous observations show that SN 1994I is a very unusual supernova, called "Type Ic," for which very few examples have been studied carefully. Following initial observations with the International Ultraviolet Explorer satellite, which demonstrated that the supernova could be detected in the ultraviolet, a preplanned series of observations was initiated by the international SINS (Supernova Intensive Survey) team, headed by Dr. Robert P. Kirshner of Harvard-Smithsonian Center for Astrophysics. The SINS group is using HST to study supernovae in the ultraviolet shortly after they are discovered, and at optical wavelengths as they become too faint to monitor from the ground. They hope to learn which stars explode as supernovae, what chemical elements are ejected by the eruption, and how to use these bright events as yardsticks for measuring the size of the universe. For example, the Supernova 1987A, located in the nearby Large Magellanic Cloud, has been studied by the SINS team since the launch of the HST in 1990 and will continue to be a target of investigations. A supernova is a violent stellar explosion that destroys a star, while ejecting the products of nuclear burning into the gas between stars. Hubble Space Telescope has the unique capability of being able to image and to measure the spectra of distant supernovae in ultraviolet light. As the M51 supernova ages, Hubble will see more deeply into the interior of the exploded star. This will allow astronomers to probe the chemical composition of the debris and to learn more about the type of star that exploded. Debris from supernova explosions play a central role in increasing the heavy element abundance of galaxies. The material that makes up the Sun, the Earth, and our bodies was once inside stars that exploded long before the solar system formed about five billion years ago. @START@Galaxy Drift Challenges Ideas About Universe's Evolution CONTACT: Ray Villard, STScI FOR RELEASE: Monday, March 21, 1994 (410) 338-4514 Karie Meyers, NOAO PRESS RELEASE NO.: STScI-PR94-15 (602) 327-5511 Dr. Marc Postman (609) 734-8003 (3/13 - 4/5) (410) 338-5072 (4/6 - ) Dr. Tod R. Lauer (609) 734-8053 (3/13 - 3/22, 3/26 - 4/5) (602) 325-9290 (3/23 - 3/25, 4/6 - ) GALAXY DRIFT CHALLENGES IDEAS ABOUT UNIVERSE'S EVOLUTION Two astronomers have discovered that our own Milky Way galaxy and most of its neighboring galaxies, contained within a huge volume of the universe, one billion light-years in diameter, are drifting with respect to the more distant universe. This startling result may imply that the universe is "lumpier" on a much larger scale than can be readily explained by any current theory. "The new observations thus strongly challenge our understanding of how the universe evolved," says Dr. Tod Lauer of the National Optical Astronomy Observatories (NOAO). This surprising conclusion comes from the deepest survey of galaxy distances to date, conducted by Dr. Tod R. Lauer in Tucson, Arizona, and Dr. Marc Postman of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. The two astronomers used NOAO telescopes at Kitt Peak National Observatory, near Tucson, Arizona, and at Cerro Tololo Inter-American Observatory, near La Serena, Chile to study galaxy motions over the entire sky out to distances of over 500 million light years. They explored a volume of space about thirty times larger than had been surveyed previously. The results of this survey will be published in the April 20 issue of The Astrophysical Journal. The expansion of the universe causes all the galaxies in the volume surveyed to be moving away from us. Galaxies at the edge of the volume are receding from us at 5% of the speed of light. The large flow that Postman and Lauer discovered comes from looking at the galaxy motions "left over" once the expansion of the universe had been accounted for. The flow means that the nearby universe, as well as expanding, appears to be drifting with respect to the more distant universe. Astronomers generally assume that the diffuse glow of microwave radiation left over from the Big Bang provides the backdrop or rest frame of the universe. In the mid 70's astronomers found that temperature of this radiation is slightly hotter towards the direction of the constellation of Leo. This effect has been interpreted to mean that the Milky Way is drifting with respect to the rest of the universe at about 380 miles per second in this direction. It has also been assumed that most of this motion is due to the gravitational attraction of more distant galaxies; however, these galaxies have never been positively identified. In the mid-80's a group of seven astronomers surveyed the motions of galaxies out to about one-third of the distance studied by Lauer and Postman, finding the galaxies to be flowing as a group with respect to the more distant universe. This team postulated that this flow was due to the gravitational pull of a large concentration of galaxies dubbed "The Great Attractor." The Great Attractor is located deep inside the volume surveyed by Postman and Lauer, however, and would not be massive enough to cause their much larger sample of galaxies to drift. In fact, the new result implies that the Milky Way and its neighbors are affected by much larger concentrations of galaxies at much larger distances than can be easily explained by popular theories of how the universe is organized. Lauer and Postman started their project in 1989 to measure the drift of the Milky Way with respect to 119 clusters of galaxies located all over the sky at distances as far as 500 million light-years. If the motion of the Milky Way was caused by galaxies closer to us than the distant clusters, as was then presumed to be the case, then its motion with respect to the clusters should have been essentially identical to that with respect to the microwave background radiation. Because the galaxy clusters are at a variety of distances from us, galaxies in the more distant clusters appear dimmer than the ones more nearby. However, once the various distances are accounted for, the brightest galaxy in each cluster is always found to give off roughly the same amount of light. Astronomers refer to such objects as "standard candles." The distances to the clusters are estimated from how fast they are moving away from us as the universe expands. If the Milky Way Galaxy is drifting, however, its motion makes measurement of the expansion speeds dependent on which direction we are looking. If the drift is not corrected for, then the cluster galaxies will appear to vary slightly in brightness in a smooth pattern across the sky. Postman and Lauer used images of the cluster galaxies to detect this pattern and determine the motion of our own galaxy. The motion of the Milky Way that Postman and Lauer measured from the distant clusters is in a completely different direction from that inferred from the microwave background. The most likely solution to this dilemma is that the clusters themselves are moving with an average velocity of 425 miles per second towards the constellation of Virgo. Because of the enormous size of the volume containing the clusters, however, this implies the existence of even more distant and massive concentrations of matter. Most theories explaining the structure of the universe predict that the universe should be nearly uniform on the scale of the Lauer and Postman cluster sample. The motion of the Milky Way and its neighbors would then be due to concentrations of mass relatively close by. If instead, the portions of the universe as big as a billion light-years in diameter are still drifting with respect to the larger universe, then the universe has structure or "lumps" of matter on much larger scales than predicted by most theories. The detection of galaxy flows across large volumes of space should improve our understanding of how the universe came to be organized the way we see it today. A more provocative but probably less likely interpretation of the Postman and Lauer result is that the large volume of clusters really is at rest, with the temperature variation of the microwave background around the sky being a relic of the conditions of the Big Bang, rather then being caused by the motion of our galaxy. In this case, the microwave temperature variation would tell about the properties of the very early universe rather than about large scale motions of galaxies. @END@
