Orbiting telescope detects sound waves from black hole

WASHINGTON -- The voice of a black hole is a deep, deep bass, 57 octaves below middle C and far beyond the hearing range of humans. The Chandra X-ray Observatory has picked up sound waves for the first time from a cluster of galaxies 250 million light years away.

Astronomers at the Institute of Astronomy in Cambridge, England, discovered the sound waves while analyzing the Chandra images of the Perseus cluster, a grouping of galaxies held in formation by the tug of a supermassive black hole.

Andy Fabian, a professor at the Institute of Astronomy, said a close study shows ripples in the X-ray pattern that are caused by sound waves excited by the energy from the black hole.

He said the sound produced by the black hole is a B flat, the same pitch as a key near middle C on the piano. But the song of the Perseus Black Hole is 57 octaves below that middle C.

The voice of the black hole is detected by analyzing the pattern of X-rays coming from superheated gases in the Perseus galactic cluster, said Fabian.

Squeezed by the gravitational pull of the black hole and the galaxies in the cluster, gases are heated to 50 million degrees, hot enough to generate X-rays. A surge of sound waves through the gases adds heat energy, causing a slight change in the pattern of X-rays.

"Sound consists of pressure waves," said Fabian. "In the gas of the Perseus cluster, the higher pressure means more X-ray emission."

The distance between sound waves determines the pitch.

For instance, in a very high pitched sound, such as the extreme upper note of a violin, the sound waves are close together and cycle many times a second. Most sounds detectable by the human ear cycle very rapidly.

But the voice of the black hole could never be heard by the human ear because there are 10 million years between each of the sound waves, "clearly not within human experience," said Fabian.

Bruce Margon of the Space Telescope Science Institute said that the Perseus Black Hole may play only one note, but it has been playing for about three billion years.

"Although this symphony does not have a lot of variety, it is surely the longest lasting symphony that we know," said Margon.

A black hole is a single point in space that is so dense with matter that its gravitational field will not permit the escape of anything, not even light. This immense gravitation pull causes gas and other matter to accelerate at a high rate of speed and to heat by millions of degrees. The action of the black hole also can create jets of matter that shoot out from opposite sides of the single point.

The jets are what causes the sound waves, said Allen. The jets compress and push away gas, leaving behind cavities. Sound waves streak away from these cavities, crash into the gas and transfer energy as heat. This heat, in turn, triggers X-rays detected by Chandra. The X-rays match the cycle of the sound waves. Thus, by measuring the distance between the waves, the researchers could determine the pitch of the black hole sound.

On the Net

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