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, an immense grouping of galaxies held in formation by the powerful tug of a supermassive black hole.

Andy Fabian, a professor at the Institute of Astronomy, said a close study of the fine detail collected by Chandra showed ripples in the X-ray pattern that were caused by sound waves excited by the energy from the black hole.

He said the sound produced by the black hole was 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. This is a tone frequency more than a million, billion times deeper than the limits of the human ear, Fabian said.

It is, he said, “the lowest note known in the universe.”

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

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 adds heat energy, causing a slight change in the pattern of X-rays.

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

In effect, he said, the sound waves cause bright and dark emissions of X-rays moving in rings away from the black hole center like ripples on the surface of a pool.

Images of a 53-hour Chandra X-ray Observatory observation, taken Aug. 8 and 10, 2002, of the central region of the Perseus galaxy cluster, left, reveal wavelike features, right, that appear to be sound waves. The voice of the Perseus Black Hole is a deep bass, 57 octaves below middle C and far beyond the hearing range of humans.

“A three dimensional analogy is when a child takes a straw and blows into a glass of water, producing a sequence of bubbles,” Fabian said. “That is like a sequence of sound waves.”

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.

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.