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Subj: CHANDRA "HEARS" A BLACK HOLE
Date: 9/9/2003 10:55:23 AM Pacific Daylight Time
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Donald Savage
Headquarters, Washington
(Phone: 202/358-1727) September 9, 2003

Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256/544-6535)

Megan Watzke
Chandra X-ray Observatory Center, CfA, Cambridge, Mass.
(Phone: 617/496-7998)

RELEASE: 03-284

CHANDRA "HEARS" A BLACK HOLE

NASA's Chandra X-ray Observatory detected sound waves,
for the first time, from a super-massive black hole. The
"note" is the deepest ever detected from an object in the
universe. The tremendous amounts of energy carried by these
sound waves may solve a longstanding problem in
astrophysics.

The black hole resides in the Perseus cluster, located 250
million light years from Earth. In 2002, astronomers
obtained a deep Chandra observation that shows ripples in
the gas filling the cluster. These ripples are evidence for
sound waves that have traveled hundreds of thousands of
light years away from the cluster's central black hole.

"We have observed the prodigious amounts of light and heat
created by black holes, now we have detected the sound,"
said Andrew Fabian of the Institute of Astronomy (IoA) in
Cambridge, England, and leader of the study.

In musical terms, the pitch of the sound generated by the
black hole translates into the note of B flat. But, a human
would have no chance of hearing this cosmic performance,
because the note is 57 octaves lower than middle-C (by
comparison a typical piano contains only about seven
octaves). At a frequency over a million, billion times
deeper than the limits of human hearing, this is the deepest
note ever detected from an object in the universe.

"The Perseus sound waves are much more than just an
interesting form of black hole acoustics," said Steve Allen,
also of the IoA and a co-investigator in the research.
"These sound waves may be the key in figuring out how galaxy
clusters, the largest structures in the universe, grow,"
Allen said.

For years astronomers have tried to understand why there is
so much hot gas in galaxy clusters and so little cool gas.
Hot gas glowing with X-rays should cool, and the dense
central gas should cool the fastest. The pressure in this
cool central gas should then fall, causing gas further out
to sink in towards the galaxy, forming trillions of stars
along the way. Scant evidence has been found for such a flow
of cool gas or star formation. This forced astronomers to
invent several different ways to explain why the gas
contained in clusters remained hot, and, until now, none of
them was satisfactory.

Heating caused by a central black hole has long been
considered a good way to prevent cluster gas from cooling.
Although jets have been observed at radio wavelengths, their
effect on cluster gas was unclear since this gas is only
detectable in X-rays, and early X-ray observations did not
have Chandra's ability to find detailed structure.

Previous Chandra observations of the Perseus cluster showed
two vast, bubble-shaped cavities in the cluster gas
extending away from the central black hole. Jets of material
pushing back the cluster gas have formed these X-ray
cavities, which are bright sources of radio waves. They have
long been suspected of heating the surrounding gas, but the
mechanism was unknown. The sound waves, seen spreading out
from the cavities in the recent Chandra observation, could
provide this heating mechanism.

A tremendous amount of energy is needed to generate the
cavities, as much as the combined energy from 100 million
supernovae. Much of this energy is carried by the sound
waves and should dissipate in the cluster gas, keeping the
gas warm and possibly preventing a cooling flow. If so, the
B-flat pitch of the sound wave, 57 octaves below middle-C,
would have remained roughly constant for about 2.5 billion
years.

Perseus is the brightest cluster of galaxies in X-rays, and
therefore was a perfect Chandra target for finding sound
waves rippling through the hot cluster gas. Other clusters
show X-ray cavities, and future Chandra observations may yet
detect sound waves in these objects.

For images and additional information on the Internet,
visit:

http://chandra.nasa.gov

http://chandra.harvard.edu

-end-

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