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, ultrahot gas that suffuses galaxy clusters. They were caused by periodic explosions from a supermassive black hole at the center of the cluster, which 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 that 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.”
As part of an ongoing project to “sonify” the universe, NASA also released similarly generated sounds of bright knots in a jet of energy shooting from a giant black hole at the center of the humongous galaxy known as M87. These sounds reach us across 53.5 million light-years as a stately succession of orchestral tones.
Yet another sonification project has been undertaken by a group led by Erin Kara, an astrophysicist at the Massachusetts Institute of Technology, as part of an effort to use light echoes from X-ray bursts to map the environment around black holes, much as bats use sound to catch mosquitoes.
All this is an outgrowth of “Black Hole Week,” an annual NASA social media extravaganza, May 2-6. As it happens this week provides a prelude to big news on May 12, when researchers with the Event Horizon Telescope, which in 2019 produced the first image of a black hole, are to announce their latest results.
Black holes, as decreed by Einstein’s general theory of relativity, are objects with gravity so strong that nothing, not even light, much less sound, can escape. Paradoxically, they can also be the brightest things in the universe. Before any sort of matter disappears forever into a black hole, theorists surmise, it would be accelerated to near-light speeds by the hole’s gravitational field and heated, swirling, to millions of degrees. This would spark X-ray flashes, generate interstellar shock waves and squeeze high-energy jets and particles across space like so much toothpaste from a tube.
In one common scenario, a black hole exists in a binary system with a star and steals material from it, which accretes into a dense, bright disk – a visible donut of doom – that sporadically produces X-ray outbursts.
Using data from a NASA instrument called the Neutron Star Interior Composition Explorer – NICER – a group led by Jingyi Wang, an MIT graduate student, sought echoes or reflections of these X-ray blasts. The time delay between the original X-ray blasts and their echoes and distortions caused by their nearness to the weird gravity of black holes offered insight into the evolution of these violent bursts.
Meanwhile, Dr. Kara has been working with education and music experts to convert the X-ray reflections into audible sound. In some simulations of this process, she said, the flashes go all the way around the black hole, generating a telltale shift in their wavelengths before being reflected.
“I just love that we can ‘hear’ the general relativity in these simulations.” Kara said in an email.
Eat your hearts out, Pink Floyd.