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1996-01-12
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For Release: August 7, 1995
Contact: Don Savage
NASA Headquarters, Washington, DC
(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)
Press Release No.: STScI-PR95-30
HUBBLE UNCOVERS SURPRISINGLY COMPLEX STRUCTURES IN RADIO GALAXIES
Probing some of the most distant and energetic galaxies in the
universe, NASA's Hubble Space Telescope has uncovered
surprisingly varied and intricate structures of stars and gas
that suggest the processes powering these so-called radio
galaxies are more complex than previously thought.
The Hubble observations, made by a team of astronomers at
Cambridge University, England, should shed light on the
nature of active galaxies, that might be powered by immense
black holes at their cores, and more generally, on galaxy
evolution. The radio galaxies observed are so far away they
existed when the universe was half its present age, and the
light is only now reaching us.
The bizarre, never-before-seen details may be a combination
of light from massive star forming regions, small satellite
dwarf galaxies, and bow shocks caused by jets of hot gas
blasted out of the galaxy's core by a suspected black hole.
The observations were made by Professor Malcolm Longair and
Philip Best of the Cavendish Laboratory, Cambridge University,
and Huub Rottgering of Leiden Observatory, The Netherlands,
who have published images of three radio galaxies (3C368, 3C324
and 3C265) in the August 1, 1995 issue of the Monthly Notices of
the Royal Astronomical Society.
The team is analyzing a sample of 28 radio galaxies that have
been imaged by Hubble in visible light, by the Very Large Array
Radio Interferometer at radio wavelengths, and by the United
Kingdom Infrared Telescope.
A radio galaxy emits powerful radio waves along two opposite
directions pointing out from the galaxy's core. The radio lobes
usually extend far beyond the host galaxy. The suspected
powerhouse behind the radio emission is a one-billion solar
mass black hole in a galaxy's core. Gaseous jets, traveling at
nearly the speed of light, blast out along the rotation axis of
the spinning black hole. These jets bore through space like a
narrow stream of water from a garden hose nozzle plowing through
sand. When they are finally stopped by the intergalactic medium,
a huge amount of energy is released in the form of radio waves.
Previous ground-based observations since 1987 have shown that, in
visible light, distant radio galaxies have an unusual elongated
structure -- unlike the classic spiral and elliptical shapes in
normal galaxies -- that align to the twin lobes of radio
emissions that are the trademark of such active galaxies. In the
Hubble views, these shapes break up into a string of bright knots
that might be regions where new stars are forming, or could be
glowing clouds of gas. In one galaxy, the knots align to the
axis of the jet, while in another case they do not, and instead
cluster around the galaxy like smaller "satellite" galaxies.
One explanation for the alignment between the invisible jets and
optical structures is that the jets trigger the formation of
stars along their paths. However, some of the galaxies emit
highly polarized light. Since this type of light is not produced
by stars, other processes must be at work. A possible
explanation is that the light from the galaxy's hidden active
nucleus is scattered in our direction by dust or electrons.
Longair, Best and Rottgering propose that the remarkable
structures seen in the Hubble images are different manifestations
of activity associated with radio galaxies. They conclude that
at least two mechanisms must be responsible for the alignment
effect, with both scattering of nuclear light and star-formation
playing a role. They also note that the period during which there
is strong radio emission is quite short relative to the total
lifetime of a galaxy, so different processes may dominate as the
radio source ages. They are planning further observations to
determine the relative importance of the different effects.
* * * * *
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 may be accessed on Internet
via anonymous ftp from ftp.stsci.edu:
GIF: /pubinfo/gif/3Cgalax.gif
JPEG: /pubinfo/jpeg/3Cgalax.jpg
The same images are available via World Wide Web from URL
http://www.stsci.edu/pubinfo/PR/95/30.html or via links in
http://www.stsci.edu/pubinfo/Pictures.html