Don Savage
Headquarters, Washington, DC              November 19, 1996
(Phone:  202/358-1547)
Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5566)
Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)
RELEASE:  96-244
HUBBLE SURVEYS THE "HOMES" OF QUASARS
       Two teams of astronomers are releasing dramatic Hubble
Space Telescope images today, which show that quasars live in
a remarkable variety of galaxies, many of which are violently
colliding.  This complicated picture suggests there may be a
variety of mechanisms -- some quite subtle -- for "turning
on" quasars, the universe's most energetic objects.
       The Hubble researchers also are intrigued by the fact
that the quasars studied do not appear to have obviously
damaged the galaxies in which they live.  This could mean
that quasars are relatively short-lived phenomena which many
galaxies, including the Milky Way, experienced long ago.
       John Bahcall of the Institute for Advanced Study,
Princeton, NJ, emphasizes that Hubble's clarity opens a
complicated picture.  "If we thought we had a complete theory
of quasars before, now we know we don't," says Bahcall.  "No
coherent, single pattern of quasar behavior emerges.  The
basic assumption was that there was only one kind of host
galaxy, or catastrophic event, which feeds a quasar.  In
reality we do not have a simple picture -- we have a mess."
        Mike Disney, University of Wales College, Cardiff,
U.K., who is the leader of the European team, says, "People
had suspected that collisions might be an important mechanism
for feeding black holes and generating the vast amounts of
energy emitted by quasars.  Now we know they are and we
didn't know that before Hubble.  This is a really exciting
achievement."
       Though a number of the images show collisions between
pairs of galaxies which could trigger the birth of quasars,
some pictures reveal apparently normal, undisturbed galaxies
possessing quasars.  "We were amazed by the beauty and
clarity of the Hubble images, as well as the diversity of
quasar environments," says Donald Schneider of Pennsylvania
State University, State College, PA.
      Discovered only 33 years ago, quasars are among the
most baffling objects in the universe because of their small
size and prodigious energy output.  Quasars are not much
bigger than Earth's solar system but pour out 100 to 1,000
times as much light as an entire galaxy containing a hundred
billion stars.
       A super massive black hole, gobbling up stars, gas and
dust, is theorized to be the "engine" powering a quasar.
Most astronomers agree an active black hole is the only
credible possibility that explains how quasars can be so
compact, variable and powerful.  Nevertheless, conclusive
evidence has been elusive because quasars are so bright they
mask any details of the "environment" where they live.
       "These problems couldn't be solved without the Hubble
Telescope," Disney said.  "I gave up on studying quasars 20
years ago, because I realized we had to wait for a space
telescope to provide a clear enough view for solving mysteries."
       Observations by the European team, using the Wide
Field Planetary Camera 2 (WFPC2) in high-resolution mode,
reveal that quasars appear to be born in environments where
two galaxies are interacting violently and probably
colliding.  "This had long been suspected as a mechanism for
igniting a quasar but no one knew whether the idea was really
right, before the Hubble," says Peter Boyce of the European team.
       "In nearly every quasar we look at we clearly see one
galaxy apparently swallowing another," Disney said.  He
selected three quasars known to be strong infrared emitters,
suggesting that they might be in spiral galaxies, which
typically contain a great deal of gas and dust.  "When we
image them with Hubble we see the most colossal smashups,
where two giant spiral galaxies like our own Milky Way have
crashed head on into one another and flung off pieces
violently in all directions.  Some of those bits seem to have
finished up in the nucleus of one of the spirals where there
is probably a giant black hole feeding on it."
       Bahcall, Schneider and Sofia Kirkahos also used the
WFPC2, but in wide-field mode, to survey 20 quasars.  Bahcall
finds about half of the quasars studied have host galaxies
which look undisturbed.  "Either the interacting companion is
very close to the nucleus and below Hubble's resolution, or
other mechanisms are at work in igniting quasars."
       Both teams agree that Hubble images do show conclusively:
       *  That most quasars lie at the cores of luminous
galaxies, both spiral and elliptical.  Though underlying
galaxies were suggested in ground-based quasar observations,
astronomers had to wait for Hubble's capabilities to show the
host galaxies clearly enough for astronomers to begin to
classify their shapes.
       *  Interactions between galaxies, either through
direct collisions or near encounters, can be important in
"turning on" a quasar, by dumping fuel onto a black hole.
However, some quasars look unperturbed, so there may be
other, more subtle mechanisms for feeding the black hole.
"Some of the galaxies we observed don't appear to know they
have a quasar in their cores," says Bahcall.  "This may be a
very important clue, since it was a completely unexpected result."
*  Quasars that are "radio quiet" are often in elliptical
galaxies, not always in spiral galaxies, as previously believed.
       Further quasar research will be challenging because of
the great distance and long time scales involved.  "It's like
having a few still shots of a football game and trying to
decipher both the rules and the final score.  It's very
challenging, and great fun, but you are obviously open to
making the most dramatic mistakes.  We'll get there in the
end but we may need a lot of Hubble pictures to be certain
what is going on," Disney said.
       Now that more is known about the environments in which
quasars exist, the teams emphasize astronomers must address
even larger puzzles.  Do most quasars flare up for a brief
period of a galaxy's life (100 million years or less)?  If
so, then most galaxies, including our Milky Way, could be
"burned out" quasars.  If, alternatively, quasars are long-
lived, it implies they are more rare.  "This means a few
extremely massive black holes formed very early in the
universe," says Disney.
       Astronomers also need to address a "chicken and egg"
problem about the birth of quasars.  Did the massive black
holes form first and the galaxies formed around them, or did
galaxies precede black holes, which quickly grew in their
cores though stellar collision and merger?
       Advanced instruments planned for Hubble should also
help pin down more details.  The Near Infrared Camera and
Multi-Object Spectrometer (NICMOS), to be installed in 1997,
and the Advanced Camera, to be installed in 1999, will have
coronagraphic devices which will block out the glare of a
quasar, allowing astronomers to see closer into a galaxy's
nucleus.  By viewing galactic structures in infrared light,
the NICMOS should be able to provide important new details
about the host galaxies of quasars.
       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.
                        - end -
EDITOR'S NOTE:  Images to accompany this release are
available to news media representatives by calling the
Headquarters Imaging Branch on 202/358-1900.
       NASA photo numbers are:
         Color:   95-HC-729                  B&W:  955-H-729
         Color:   95-HC-730                  B&W:  955-H-730
       The images also are available electronically through
the Internet via World Wide Web, ftp or Gopher.  The Internet
addresses are:
   ftp:       ftp.stsci.edu   (IP address:  130.167.1.2)
   WWW URL:   http://www.stsci.edu
   Gopher:    www.stsci.edu
The image file name is:
     /pubinfo/gif/N132D.gif   OR   /pubinfo/jpeg/N132D.jpg