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From: NASANews@hq.nasa.gov
Date: Thu, 14 May 1998 13:19:25 -0400 (EDT)
Fwd Date: Sun, 17 May 1998 08:23:10 -0400
Subject: Hubble Provides Multiple Views of How to Feed a

Douglas Isbell
Headquarters, Washington, DC                         May 14, 1998
(Phone:  202/358-1753)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)

RELEASE:  98-71

HUBBLE PROVIDES MULTIPLE VIEWS OF HOW TO FEED A BLACK HOLE

     Astronomers have obtained an unprecedented look at the
nearest example of galactic cannibalism -- a massive black hole
hidden at the center of a nearby giant galaxy that is feeding on a
smaller galaxy in a spectacular collision.  Such fireworks were
common in the early universe, as galaxies formed and evolved, but
are rare today.

     Although the cause-and-effect relationships are not yet
clear, the views provided by complementary images from two
instruments aboard NASA's Hubble Space Telescope are giving
astronomers new insights into the powerful forces being exerted in
this complex maelstrom.  Researchers believe these forces may even
have shifted the axis of the massive black hole from its expected
orientation.

     The Hubble wide-field camera visible image of the merged
Centaurus A galaxy, also called NGC 5128, shows in sharp clarity a
dramatic dark lane of dust girdling the galaxy.  Blue clusters of
newborn stars are clearly resolved, and silhouettes of dust
filaments are interspersed with blazing orange-glowing gas.
Located only 10 million light-years away, this peculiar-looking
galaxy contains the closest active galactic nucleus to Earth and
has long been considered an example of an elliptical galaxy
disrupted by a recent collision with a smaller companion spiral galaxy.

     Using the infrared vision of Hubble, astronomers have
penetrated this wall of dust for the first time to see a twisted
disk of hot gas swept up in the black hole's gravitational
whirlpool. The suspected black hole is so dense it contains the
mass of perhaps a billion stars, compacted into a small region of
space not much larger than our Solar System.

     Resolving features as small as seven light-years across,
Hubble has shown astronomers that the hot gas disk is tilted in a
different direction from the black hole's axis -- like a wobbly
wheel around an axle. The black hole's axis is identified by the
orientation of a high-speed jet of material, glowing in X-rays and
radio frequencies, blasted from the black hole at 1/100th the
speed of light.

     This gas disk presumably fueling the black hole may have
formed so recently it is not yet aligned to the black hole's spin
axis, or it may simply be influenced more by the galaxy's
gravitational tug than by the black hole's.

     "This black hole is doing its own thing. Aside from receiving
fresh fuel from a devoured galaxy, it may be oblivious to the rest
of the galaxy and the collision," said Ethan Schreier of the Space
Telescope Science Institute, Baltimore, MD.  Schreier and an
international team of co-investigators used Hubble's Near Infrared
Camera and Multi-Object Spectrometer to probe deeper into the
galaxy's mysterious heart than anyone has before.

     The hot gas disk viewed by Hubble investigators is
perpendicular to the galaxy's outer dust belt, while the black
hole's own internal accretion disk of superhot gas falling into it
is tilted approximately diagonally to these axes.

     "We have found a complicated situation of a disk within a
disk within a disk, all pointing in different directions,"
Schreier said.  It is not clear if the black hole was always
present in the host galaxy or belonged to the spiral galaxy that
fell into the core, or if it is the product of the merger of a
pair of smaller black holes that lived in the two once-separate
galaxies.

     Having an active galaxy just 10 million light-years away from
Earth rather than hundreds of millions or billions of light-years
distant offers astronomers a unique laboratory for understanding
the elusive details of the behavior of supermassive black holes as
fueled by galaxy collisions.

     "Though Hubble has seen hot gas disks around black holes in
other galaxies, the infrared camera has for the first time allowed
us to peer at this relatively nearby, very active, but obscured
black hole region," Schreier added.

     The team of astronomers is awaiting further Hubble data to
continue its study of the disk, as well as ground-based
spectroscopic observations to measure the velocity of entrapped
material around the black hole. This will allow the astronomers to
better calculate the black hole's mass.  The current results are
scheduled to appear in the June 1, 1998 issue of Astrophysical
Journal Letters.

                           - end -

EDITORS NOTE:  Images and further information related to these
results are available on the Internet at the following URLs:
             http://oposite.stsci.edu/1998/14
             http://oposite.stsci.edu/pubinfo/latest.html or
             http://oposite.stsci.edu/pubinfo/pictures.html
     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                    B&W
            98-HC-176                98-H-176
            98-HC-177                98-H-177