By Dr David Whitehouse
BBC News Online science editor
Astronomers have detected sound waves from a super-massive black hole. The "note" is the deepest ever detected from an object in the
The black hole lives in the Perseus cluster of galaxies, located 250
million light-years away.
Sound waves ripple through the hot gas
The tremendous amounts of energy carried from the black hole by these
sound waves may solve a longstanding problem in
The pitch of the sound can be determined. Although far too low to be heard, it is calculated to be B flat.
Last year astronomers obtained an image from the orbiting Chandra X-ray telescope showing ripples in the gas filling the Perseus galactic cluster.
According to the researchers the ripples are evidence for sound waves that have travelled hundreds of thousands of light years from the cluster's central black hole.
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 it because the note is 57 octaves lower than middle-C.
With a frequency over a million, billion times
deeper than the limits of human hearing, it 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," says Steve Allen of the Institute of Astronomy in Cambridge, England.
X-rays from the Perseus cluster
"These sound waves may be the key in figuring out how galaxy
clusters, the largest structures in the Universe, grow."
Astronomers are puzzled because there is
so much hot gas in galaxy clusters and so little cool gas.
The hot gas should cool, and the dense
central gas should cool the fastest.
Then the pressure in this
cool central gas should fall, causing gas further out
to sink in towards the galaxy, forming trillions of stars
along the way. But this is not what is seen.
Heating caused by a central black hole has long been
considered a good way to prevent cluster gas from cooling.
Previous Chandra observations of the Perseus cluster showed
two vast, bubble-shaped cavities in the cluster gas
extending away from the central black hole.
Sound waves spreading out from the cavities could
provide the much sought after heating mechanism.
Researchers calculate that a tremendous amount of energy is needed to generate the cavities, as much as the combined energy from 100 million exploding stars.
Much of this energy could be carried by the sound
waves that should keep the
gas warm. 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