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ESA Information Note - "Hubble provides multiple views of how to feed a black hole"

> ----------------------------------------------------------
> 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 the
> 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.
> 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
> GIF and JPEG images are available via anonymous ftp to
> oposite.stsci.edu
> in /pubinfo/jpeg/9814a.jpg, /pubinfo/jpeg/9814.jpg,
> /pubinfo/gif/9814a.gif and /pubinfo/gif/9814b.gif.
> 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 ESA
> and NASA.
> For further information, please contact : ESA Public Relations
> Division
> Tel: +33(0) Fax: +33(0)
> Prof. Piero Benvenuti Head of European Coordination Facility for the
> Tel: +49.(0) Fax: +49(0)