Cosmic battle creates Milky-Way sized tunnel (Forwarded)

Public Affairs Office
Naval Research Laboratory
Washington, D.C.

Contact:
NRL Public Affairs, 202-767-2541

1/12/2006

NRL Press Release: 1-06r

Cosmic battle creates Milky-Way sized tunnel

A team of astronomers is announcing today that they have discovered a
giant Milky Way-sized tunnel filled with high energy particles in a
distant galaxy cluster. These new findings are of special interest to
astronomers as they may provide the missing evolutionary link necessary to
understand the cycle of birth and death, as well as the environmental
impact, of radio jets which result from ravenous supermassive black holes
within giant galaxies. The report is being presented to the American
Astronomical Society meeting in Washington, DC, by Dr. Tracy Clarke of
Interferometrics, Inc. in Herndon, VA, and the Naval Research Laboratory
(NRL) in Washington, DC; along with collaborators Dr. Craig Sarazin of the
University of Virginia in Charlottesville, VA; Dr. Elizabeth Blanton of
Boston University in Boston, MA; Dr. Namir Kassim, also of NRL; and Dr.
Doris Neumann of CEA in Saclay, France.

Using the Chandra X-ray Observatory to study the multi-million degree gas
in the galaxy cluster Abell 2597, the scientists discovered an unusual
X-ray tunnel large enough to fit the entire Milky Way galaxy inside. The
cluster, located at a distance of roughly one billion light years,
contains a tunnel in the hot gas, which measures nearly 110 thousand light
years by 36 thousand light years in size. The tunnel, which appears to
originate near the core of the central giant galaxy in the cluster, may be
more than 200 million years old.

A constant battle is being waged in the central regions of clusters of
galaxies. The hot gas invades the core of the cluster and feeds the
supermassive black hole that is lurking there. As the black hole eats more
and more, it becomes active and nearby material is funneled into powerful
jets of highly energetic particles (so-called radio jets) outward into the
hot gas. These relativistic jets, containing particles moving at close to
the speed of light, carve out bubbles while they expand, pushing aside the
hot gas. Like a poorly planned invasion, these jets cut off the fuel
supply to the central black hole, leading to a temporary starvation.
Without fuel to maintain the attack, the radio jets cease and the hot gas
once again is able to invade the central region of the cluster and the
battle begins again.

The new observations of a tunnel connecting from the central supermassive
black hole to a distance nearly seven times the radio galaxy size in Abell
2597 suggest that the picture may be more complicated than previously
thought. Past radio observations at a wavelength of roughly 4 cm,
published in 1995 by Sarazin and collaborators, showed that this system
was host to a small radio galaxy only 25 thousand light years across.
Recently, Clarke and collaborators obtained new low frequency (90 cm
wavelength) radio observations using the National Science Foundation's
Very Large Array (VLA), which shed new light on the violent history of the
central radio galaxy and its connection to the X-ray tunnel. "Low
frequency radio observations are sensitive to the oldest energetic
particles thus giving us a means to step even further back in time and
look into the past lives of radio galaxies," explains Dr. Clarke. These
new observations revealed that the X-ray tunnel is filled with old
particles, invisible at shorter wavelengths, which likely originate from
the past outbursts of the black hole.

"X-ray and radio observations show that the central supermassive black
holes in clusters are at war with the surrounding X-ray gas" says Dr.
Sarazin. "In Abell 2597, the small young radio source being inflated by
the supermassive black hole at the center of this cluster is the start of
a new battle. The tunnel is like a scar left from previous battles,
showing that this war has been going on for billions of years. The fact
that the tunnel connects back to the supermassive black hole suggests that
the black hole is trying the breach the clusters defenses in the same area
of the gas where it has been successful in the past."

Astronomers are far from understanding the complex interactions between
radio jets and the hot gas in galaxy clusters. Observations of new
phenomena such as the tunnel in Abell 2597 are critical as they provide
additional clues to how the battle is waged between the inward flow of the
hot gas and the outward march of the radio jets. Further progress in the
field will require sensitive observations at even longer wavelengths, but
unfortunately the current suite of low frequency radio telescopes are
already at their limits of sensitivity and resolution.

To address this shortcoming, astronomers at several institutions,
collectively known as the Southwest Consortium, are contributing to an
effort to build the world's largest and most sensitive low-frequency
telescope, called the Long Wavelength Array (LWA). The LWA will operate at
wavelengths between 15 and 3.75 meters (or 20 and 80 Megahertz) and has
the potential to revolutionize future studies of radio galaxies and galaxy
clusters.

Current plans call for the LWA to be sited near the VLA in New Mexico.
"Ironically the LWA will operate at the same frequencies at which Carl
Jansky first discovered extra-terrestrial radio emission, thus
representing a return to the very roots of radio astronomy," notes Dr.
Namir Kassim, a radio astronomer in NRL's Remote Sensing Division.

This project was supported by the National Aeronautics and Space
Administration through Chandra X-ray Observatory awards. Basic research in
radio astronomy at NRL is supported by the Office of Naval Research. The
National Radio Astronomy Observatory operates the VLA for the National
Science Foundation under a cooperative agreement by Associated
Universities, Inc.

IMAGE CAPTIONS:
[http://www.nrl.navy.mil/pao/PressRel...Fig1-1-06r.jpg (50KB)]
The top image show the disturbed hot multi-million degree gas in Abell
2597 and the dashed rectangle shows the scale of the two lower images.
Resembling the center of an apple invaded by worms, the X-ray emission in
the lower left image shows a number of dark holes as well as a tunnel in
the hot gas. The X-ray image has been processed to remove the smooth
emission and highlight the central structure, similar to slicing through
an apple to look at a cross-section of the core. The image on the right
shows an overlay (in blue) of the low frequency radio emission from the
central supermassive black hole which has carved out the Milky-Way sized
tunnel in the hot gas. This image was presented to the American
Astronomical Society meeting in Washington, DC on January 12, 2006.

PHOTO CREDIT: NRL/T. Clarke et al.