For the first time, sound waves have been detected from a supermassive black
hole by using NASA’s Chandra X-ray Observatory. 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

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

“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,

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 was them

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. These X-ray cavities, which are bright sources of radio waves,
have been formed by jets of material pushing back the cluster gas. 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.

Science Contacts:

* Prof. Andy Fabian, Institute of Astronomy,, +44
1223 337548 (switchboard) 337509 (direct)

* Dr. Steven Allen, Institute of Astronomy,, +44
1223 337548 (switchboard) 330803 (direct)

* Dr. Kim Weaver, Goddard Space Flight Center,, 301.286.4256

* Dr. Bruce Margon, Space Telescope Science Institute,, 410.338.4459

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