From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: HST Discovers Disks Fueling a Likely Black Hole
Originator: sah@wfpc3
Keywords:  HST
Organization: Jet Propulsion Laboratory
Date: Fri, 20 Nov 1992 16:45:15 GMT

Paula Cleggett-Haleim
Headquarters, Washington, D.C.             November 19, 1992
(Phone:  202/358-0883)

Jim Elliott
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-6256)

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


RELEASE:  92-208

HUBBLE DISCOVERS A DISK FUELING A LIKELY BLACK HOLE

     Astronomers using NASA's Hubble Space Telescope (HST)
have gotten their best look yet at the disk of material that
surrounds and is being pulled into a suspected black hole.

     The disk is at the core of a galaxy in the Virgo Cluster
45 million light-years from Earth.  Dr. Walter Jaffe of
Leiden Observatory in The Netherlands said the disk is tipped
about 60 degrees -- enough to provide astronomers with a
clear view of the galaxy's bright hub.

     "The nucleus is probably the home of a black hole with a
mass 10 million times that of our sun," Jaffe said.  "This is
our best view to date of the immediate surrounding of the
nucleus of an active galaxy," the name given galaxies that
emit especially strong radiation indicating that they harbor
powerful energy sources.

     "This is the first case where we can follow the disk's
gas in an orderly way down to the immediate environment of
the black hole," said co-investigator Dr. Holland Ford of The
Johns Hopkins University in Baltimore.

     The observations, made with the Wide Field/Planetary
Camera (WF/PC) in the planetary camera mode, make a strong
contribution to mounting evidence for the existence of black
holes in the universe, the two astronomers said.

     A black hole is a theoretical object that is believed to
form after a massive star collapses.  The star's matter is so
densely compacted that it has a powerful gravitational pull
that traps all matter that comes near it.

     Black holes to date are theoretical because their
gravitational pull is so great that not even light can
escape.  Therefore, they cannot be seen.  Astronomers infer a
black hole's existence by its gravitational influence on the
motion of stars and other material near it.

     The galaxy, designated NGC 4261, was selected for study
because it is one of the brightest in the Virgo Cluster.

     "The galaxy is unremarkable in visible light," said
Jaffe.  "However, observations with radio telescopes show a
pair of opposed jets emanating from the nucleus and spanning
a distance of 88,000 light-years."  Spectroscopic data from
the Observatory del Roque de los Muchachos in the Canary
Islands show ionized gas in the nucleus moving at speeds
approaching several million miles an hour, or one percent of
the speed of light.

     "Most astronomers believe both phenomena, which have
been seen earlier in radio galaxies and quasars (active
nuclei of remote galaxies), to be caused by material being
swallowed by massive black holes hiding in the nuclei of
large galaxies," said Ford.

     The dark, dusty disk which is 300 light-years across,
represents the cold outer region which extends inwards to
within a few hundred million miles of the suspected black
hole.  This disk feeds matter into the black hole, where
gravity compresses and heats the material to tens of millions
of degrees.  Some hot gas squirts out from the black hole's
vicinity like twin streams of water from a lawn sprinkler.

     "The spin axis of the disk orients the radio jets," said
Ford.  "The cooler, outer regions of the washer-shaped disk
confine the ionizing radiation from the hot interior into a
pair of cones whose axes are parallel to the radio jets."

     Because dust and cool gas (neutral hydrogen) are not
normally found in elliptical galaxies, the presence of a disk
at all provides a mystery.  Much of the dust should have been
destroyed quickly by the hot gas in the galaxy.  One possible
explanation is that the dust is a remnant of a spiral galaxy
that was swallowed by NGC 4261 in the recent past.

     After the scheduled Space Shuttle servicing mission for
Hubble in late 1993, the researchers hope to use spectroscopy
to study the motion of the gas within a few dozen light-years
of the black hole.  This might allow them to prove the
existence of the black hole by accurately measuring its mass.

     The researchers also hope to use spectroscopy to infer
the thickness and shape of the inner parts of the disk that
are too small to be seen even with the HST.

     The results are to be published in the Astrophysical
Journal.  Co-investigators with Ford and Jaffe are Robert
O'Connell (University of Virginia, Charlottesville), Laura
Ferrares (Johns Hopkins University, Baltimore) and Frank van
den Bosch (Leiden Observatory, The Netherlands).

     The Hubble Space Telescope is a project of international
cooperation between NASA and the European Space Agency.

- end -

     Photographs and a video to illustrate this release are
available to news media by calling NASA's Broadcast and
Imaging Branch on 202/453-8375.

     Color:      92-HC-708         92-HC-709
     B&W:      92-H-767            92-H-768
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    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
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