The sounds of a black hole

In space you can’t hear a black hole scream, but apparently you can hear it sing.

In 2003 astrophysicists working with NASA’S orbiting Chandra X-ray Observatory detected a pattern of ripples in the X-ray glow of a giant cluster of galaxies in the constellation Perseus. They were pressure waves — that is to say, sound waves — 30,000 light-years across and radiating outward through the thin, ultra hot gas that suffuses galaxy clusters. They were caused by periodic explosions from a supermassive black hole at the centre of the cluster that is 250 million light-years away and contains thousands of galaxies.

With a period of oscillation of 10 million years, the sound waves were acoustically equivalent to a B-flat 57 octaves below middle C, a tone that the black hole has apparently been holding for the last two billion years. Astronomers suspect these waves act as a brake on star formation, keeping the gas in the cluster too hot to condense into new stars. The Chandra astronomers recently “sonified” these ripples by speeding up the signals to 57 or 58 octaves above their original pitch, boosting their frequency quadrillions of times to make them audible to the human ear. As a result, the rest of us can now hear the intergalactic sirens singing.

Through these new cosmic headphones, the Perseus black hole makes eerie moans and rumbles that reminded this listener of the galumphing tones marking an alien radio signal that Jodie Foster hears through headphones in the science fiction film Contact.

All this is an outgrowth of “Black Hole Week,” an annual NASA social media extravaganza, May 2-6.