Black Hole Sound Waves

Yet scant evidence has been found for flows of cool gas or for star formation. This forced astronomers to invent several different ways to explain how gas contained in clusters remained hot. None of them were satisfactory.

Black hole sound waves, however, might do the trick.

more An illustration of cavities and sound waves in the hot gas filling the Perseus cluster.

Previous Chandra observations of the Perseus cluster reveal two vast, bubble-shaped cavities extending away from the central black hole. These cavities have been formed by jets of material pushing back the cluster gas. The jets, which are a counter-intuitive side effect of the black hole gobbling matter in its vicinity, have long been suspected of heating the surrounding gas. But the exact 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 supernovas. 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 those clusters, too.