The Starbase One Astronomy & Space Collection/STARBASE_ONE.ISO/hst/95_44.txt

Text File | 1996-01-12 | 7KB | 142 lines

EMBARGOED UNTIL: 3:00 PM (EST) November 2, 1995

CONTACT:  Don Savage
          NASA Headquarters, Washington, DC
          (Phone: [phone])

          Fred Brown
          Goddard Space Flight Center, Greenbelt, MD
          (Phone: [phone])

          Ray Villard
          Space Telescope Science Institute, Baltimore, MD
          (Phone: [phone])

PRESS RELEASE NO.: STScI-PR95-44


  EMBRYONIC STARS EMERGE FROM INTERSTELLAR "EGGS"

Eerie, dramatic new pictures from NASA's Hubble Space Telescope show
newborn stars emerging from "eggs" -- not the barnyard variety -- but
rather dense, compact pockets of interstellar gas called evaporating
gaseous globules (EGGs).  Hubble found the "EGGs," appropriately
enough, in the Eagle nebula, a nearby star-forming region 7,000 light-
years away in the constellation Serpens.

"For a long time astronomers have speculated about what processes
control the sizes of stars -- about why stars are the sizes that they
are," said Jeff Hester of Arizona State University, Tempe, AZ.  "Now in
M16 we seem to be watching at least one such process at work right in
front of our eyes."

Striking pictures taken by Hester and co-investigators with Hubble's
Wide Field and Planetary Camera 2 (WFPC2) resolve the EGGs at the tip
of finger-like features protruding from monstrous columns of cold gas
and dust in the Eagle nebula (also called M16 -- 16th object in the
Messier catalog).  The columns -- dubbed "elephant trunks" -- protrude
from the wall of a vast cloud of molecular hydrogen, like stalagmites
rising above the floor of a cavern.  Inside the gaseous towers, which
are light-years long, the interstellar gas is dense enough to collapse
under its own weight, forming young stars that continue to grow as they
accumulate more and more mass from their surroundings.

Hubble gives a clear look at what happens as a torrent of ultraviolet
light from nearby young, hot stars heats the gas along the surface of
the pillars, "boiling it away" into interstellar space -- a process
called "photoevaporation.  "The Hubble pictures show photoevaporating
gas as ghostly streamers flowing away from the columns.  But not all of
the gas boils off at the same rate.  The EGGs, which are denser than
their surroundings, are left behind after the gas around them is gone.

"It's a bit like a wind storm in the desert," said Hester.  "As the
wind blows away the lighter sand, heavier rocks buried in the sand are
uncovered.  But in M16, instead of rocks, the ultraviolet light is
uncovering the denser egg-like globules of gas that surround stars that
were forming inside the gigantic gas columns."

Some EGGs appear as nothing but tiny bumps on the surface of the
columns.  Others have been uncovered more completely, and now resemble
"fingers" of gas protruding from the larger cloud. (The fingers are gas
that has been protected from photoevaporation by the shadows of the
EGGs).  Some EGGs have pinched off completely from the larger column
from which they emerged, and now look like teardrops in space.

By stringing together these pictures of EGGs caught at different stages
of being uncovered, Hester and his colleagues from the Wide Field and
Planetary Camera Investigation Definition Team are getting an
unprecedented look at what stars and their surroundings look like
before they are truly stars.

"This is the first time that we have actually seen the process of
forming stars being uncovered by photoevaporation," Hester emphasized.
"In some ways it seems more like archaeology than astronomy.  The
ultraviolet light from nearby stars does the digging for us, and we
study what is unearthed."

"In a few cases we can see the stars in the EGGs directly in the WFPC2
images," says Hester.  "As soon as the star in an EGG is exposed, the
object looks something like an ice cream cone, with a newly uncovered
star playing the role of the cherry on top."

Ultimately, photoevaporation inhibits the further growth of the
embyronic stars by dispersing the cloud of gas they were "feeding"
from.  "We believe that the stars in M16 were continuing to grow as
more and more gas fell onto them, right up until the moment that they
were cut off from that surrounding material by photoevaporation," said
Hester.

This process is markedly different from the process that governs the
sizes of stars forming in isolation.  Some astronomers believe that,
left to its own devices, a star will continue to grow until it nears
the point where nuclear fusion begins in its interior.  When this
happens, the star begins to blow a strong "wind" that clears away the
residual material.  Hubble has imaged this process in detail in
so-called Herbig-Haro objects.

Hester also speculated that photoevaporation might actually inhibit the
formation of planets around such stars.  It is not at all clear from
the new data that the stars in M16 have reached the point where they
have formed the disks that go on to become solar systems," said Hester,
"and if these disks haven't formed yet, they never will."

Hester plans to use Hubble's high resolution to probe other nearby
star-forming regions to look for similar structures.  "Discoveries
about the nature of the M16 EGGs might lead astronomers to rethink some
of their ideas about the environments of stars forming in other
regions, such as the Orion Nebula," he predicted.

                                * * * * * *

The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA), for NASA, under
contract with the Goddard Space Flight Center, Greenbelt, MD.  The
Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).

Image files in GIF and JPEG format and captions may be accessed on
Internet via anonymous ftp from ftp.stsci.edu in /pubinfo:

                                   GIF                   JPEG
PRC95-44a   M16  3 Pillars    gif/M16Full.gif     jpeg/M16Full.jpg
PRC95-44b   M16  1 Pillar     gif/M16WF2.gif      jpeg/M16WF2.jpg
PRC95-44c   M16 B&W Detail    gif/M16HaBW.gif     jpeg/M16HaBW.jpg

Higher resolution versions (300dpi JPEG) of the release photographs
will be available temporarily in /pubinfo/hrtemp: 95-44a.jpg,
95-44b.jpg and 95-44c.jpg.

GIF and JPEG images, captions and press release text are available via
World Wide Web at URL http://www.stsci.edu/pubinfo/PR/95/44.html, or
via links in http://www.stsci.edu/Latest.html and
http://www.stsci.edu/pubinfo/Pictures.html.

Space Telescope Science Institute press release text and other
information are available automatically by sending an Internet
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Don't use quotes or user/account names; i.e., someone named Jane Doe
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