The Starbase One Astronomy & Space Collection/STARBASE_ONE.ISO/hstbig/95_47.txt

Text File | 1995-12-04 | 8KB | 150 lines

EMBARGOED UNTIL: 6:30 AM (EST) December 4, 1995

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

          Simon Vermeer
          European Space Agency, Paris, France
          (Phone:  [phone])

          Holland Ford
          Johns Hopkins University, Baltimore, MD
          (Phone: [phone])

PRESS RELEASE NO.: STScI-PR95-47

HUBBLE FINDS A NEW BLACK HOLE -- AND UNEXPECTED NEW MYSTERIES

Confirming the presence of yet another super-massive black hole in the
universe, astronomers using the Hubble Space Telescope have found
unexpected new mysteries.  The black hole, and a 800 light-year-wide
spiral-shaped disk of dust fueling it, are slightly offset from the
center of their host galaxy, NGC 4261, located 100 million light-years
away in the direction of the constellation Virgo.

This discovery is giving astronomers a ringside seat to bizarre,
dynamic processes that may involve a titanic collision and a runaway
black hole.  This relatively nearby galaxy could shed light on how far
more distant active galaxies and quasars produce their prodigious
amounts of energy.

The results are being presented by the team, consisting of Laura
Ferrarese and Holland Ford of the Johns Hopkins University, Baltimore,
MD., and Walter Jaffe of Leiden University, The Netherlands, at a press
conference at the European Space Agency, Paris, France, in conjunction
with the Science With Hubble Space Telescope II workshop.

"I'm delighted by this new finding.  It doesn't fit our expectations,
and this should lead us to a new understanding of black holes," said
Holland Ford.  "The new Hubble observations have moved us beyond the
question of whether black holes exist.  Now we can work on the
demographics of black holes and address a number of other questions:
does every galaxy have a black hole?  How do these extraordinary
engines work?"

Predicted by Einstein's general theory of relativity, a black hole is
an extremely compact and massive object that has such a powerful
gravitational field that nothing, not even light can escape.  This is
the second super-massive black hole confirmed by Hubble.  By measuring
the speed of gas swirling around the black hole, the team of
astronomers was able to calculate its mass to be 1.2 billion times the
mass of our Sun, yet concentrated into a region of space not much
larger than our solar system.

The strikingly geometric disk -- which  contains enough mass to make
100,000 stars like our Sun -- was first identified in Hubble
observations made in 1992.  These new Hubble images reveal for the
first time structure in the disk, which may be produced by waves or
instabilities in the disk.

Prior to Hubble observations, astronomers did not think dust was common
in elliptical galaxies like NGC 4261, which were thought to have
stopped making stars long ago due to the absence of the requisite raw
materials: interstellar gas and dust.  However, Hubble is showing that
dust and beautiful disks are common in the centers of elliptical
galaxies.  The most conventional explanation is that the disk is the
remnant of a smaller galaxy that fell into the core of NGC 4261.   The
black hole will swallow the gas from the intruder over the next 100
million years, and in the process produce spectacular fireworks,
researchers predict.

Such collisions may have been more common in the past, when the
expanding universe was smaller.  This would help explain the abundance
of quasars and active galaxies in the distant past.  However, according
to theoretical simulations, it's difficult, dynamically, to get an
intruder galaxy to plunge directly into a galaxy's core.  Another
possibility is that dust ejected from ancient stars in the galaxy has
fallen into the core and formed a disk.  But this does not explain why
the disk is off-center, which is evidence for a dynamic close
encounter.

Equally as puzzling is the discovery that the black hole is offset from
the center of the galaxy, and the disk's center as well.  Because the
black hole is the astronomical equivalent of the proverbial
"1,000-pound gorilla" - how do you move it around?   Presumably, the
black hole was at the center of the galaxy, but something has pulled it
20 light-years from the center, according to the Hubble observations.
However, the black hole is so massive it's hard to imagine how it could
have been moved.

One exotic idea is that the black hole is self-propelled.  The cold,
dusty disk serves as a rocket "fuel tank" by feeding material onto the
black hole where gravity compresses and heats it to tens of millions of
degrees.  Hot gas exhausts out from the black hole's vicinity producing
the radio jets observed by radio telescopes as twin-lobe structures
extending far beyond the galaxy. This exhaust may be pushing the black
hole across space just like a rocket engine which propels an object by
rapidly ejecting mass.

Hubble is ideally suited for hunting super-massive black holes in the
universe. With the astronomical equivalent of surgical precision,
Hubble's spectrographs can measure the rotation of gas near enough to a
suspected black hole to capture its unmistakable gravitational
signature.  The speed of gas orbiting a back hole will rapidly increase
toward the center of the disk - just as the planets closer to our Sun
orbit faster.

To date two other galaxies have confirmed black holes.  Hubble detected
a 2.4-billion-solar-mass black hole was identified in the core of
elliptical galaxy M87 in 1994, and later that year, astronomers using a
radio telescope array to examine the dynamics of a thin, warped disk of
molecules deep in the core of spiral galaxy NGC 4258 measured a
40-million-solar-mass black hole.

Ford and his colleagues continue using Hubble to survey both active and
quiescent galaxies to determine if black holes are commonly found in
most galaxies.

                                 * * * *

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, captions, and press release text
may be accessed on Internet via anonymous ftp from ftp.stsci.edu in
/pubinfo:

                           GIF                   JPEG
PRC95-47  NGC 4261 Core  gif/NGC4261C.gif     jpeg/NGC4261C.jpg

Higher resolution digital versions (300 dpi JPEG) of the release
photograph will be available temporarily in /pubinfo/hrtemp:
95-47.jpg.

GIF and JPEG images, captions and press release text are available via
World Wide Web at URL http://www.stsci.edu/pubinfo/PR/95/47.html, or
via links in http://www.stsci.edu/pubinfo/Latest.html, and in
http://www.stsci.edu/pubinfo/Pictures.html.

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