Scientists Observe Light ‘Echoes’ Coming from Black Holes, ‘Sonify’ Them with Eerie Sounds

MIT astronomers have observed “light echoes” coming from nearby black hole binary systems and “sonified” them with eerie, otherworldly sounds.

In a new study published in the Astrophysical Journal astronomers at MIT describe the “light echoes” coming off of the accretion disks and coronae around furiously spinning black holes. Furthermore, one of the study’s authors took the light echoes—generated by the delay between two types of X-ray light—and, along with several colleagues, “sonified” them; enlivening them with some very creepy sounds.

To observe these light echoes the astronomers used a new automated search tool, dubbed the “Reverberation Machine,” to search through satellite data from NICER—NASA’s high-time-resolution X-ray telescope aboard the International Space Station (ISS)—and look for signs of light echoes from “black hole X-ray binaries”; that is, from solar systems with stars orbiting, and sometimes being “eaten away” by, black holes.

In all, the astronomers’ tool turned up eight new echoing black hole binaries in the Milky Way. Previously, astronomers were only aware of two such systems in our galaxy.

As for what the light echoes actually are? MIT notes in a press release they represent time delays between two types of X-ray light: light emitted directly from the corona of a black hole—the area of highly energetic particles that generate X-ray light, right outside of a black hole’s boundary—and light from the corona that bounces off the accretion disk of inspiraling gas and dust around the black hole.

“We’re at the beginnings of being able to use these light echoes to reconstruct the environments closest to the black hole,” Erin Kara, study co-author and assistant professor of physics at MIT, says in the press release. “Now we’ve shown these echoes are commonly observed, and we’re able to probe connections between a black hole’s disk, jet, and corona in a new way,” Kara adds.

By comparing the echoes across systems, the astronomers were able to piece together a general picture of how these light echoes are generated. MIT notes that “Across all systems, they observed that a black hole first undergoes a ‘hard’ state, whipping up a corona of high-energy photons along with a jet of relativistic particles that is launched away at close to the speed of light.” Then at some point thereafter, the black hole “gives off one final, high-energy flash, before transitioning to a ‘soft,’ low-energy state.”

In a tweet threadposted, in part, above and below—Kara summarizes the study’s findings. She notes that, critically, the study’s lead author, MIT grad student Jingyi Wang, observed that during the transition from “hard” state to “soft” one, the lags in the light reverberations became roughly 10 times longer; furthermore, Kara notes that enigmatic “Quasi Periodic Oscillations” (or QPOs)—that is, the “flickering” of the X-ray light through certain frequencies—grew faster as the reverberation lags grew shorter. But then, during the state transition, broke its coupling—meaning the QPOs became shorter while the lags became longer.

Kara says she and her colleagues interpret the longer reverberation lags as a result of a corona’s “last hurrah” before “shutting down in the soft state.”

In the video at top, Kara, who worked with MIT education and music scholars Kyle Keane and Ian Condry, provides a “sonified” version of “typical” light echoes emanating from a black hole binary; meaning Kara et al. converted the emissions from a typical X-ray echo into audible sound waves.

And yes, the emissions do indeed “sound” like some horrific interlude from 2001: A Space Odyssey.

Feature image: Aurore Simonnet and NASA’s Goddard Space Flight Center

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