Hear the Eerie Sounds of a Black Hole Echo – Search Reveals 8 New Sources of Black Hole Echoes

In this illustration, a black hole pulls material off a neighboring star and into an accretion disk. Credit: Aurore Simonnet and NASA’s Goddard Space Flight Center

New findings will help scientists trace a[{” attribute=””>black hole’s evolution as it feeds on stellar material.

Tens of millions of black holes are strewn across our


This final flash may be a sign that a black hole’s corona, the region of high-energy

In a similar fashion, the MIT team is looking to map the immediate vicinity of a black hole using X-ray echoes. The echoes represent time delays between two types of X-ray light: light emitted directly from the corona, and light from the corona that bounces off the accretion disk of inspiraling gas and dust.

The time when a telescope receives light from the corona, compared to when it receives the X-ray echoes, gives an estimate of the distance between the corona and the accretion disk. Watching how these time delays change can reveal how a black hole’s corona and disk evolve as the black hole consumes stellar material.

Echo evolution

In their new study, the team developed a search algorithm to comb through data taken by

As a side project, Kara is working with MIT education and music scholars, Kyle Keane and Ian Condry, to convert the emission from a typical X-ray echo into audible sound waves. Take a listen to the sound of a black hole echo here:

Credit: Sound computed by Kyle Keane and Erin Kara, MIT. Animation computed by Michal Dovciak, ASU CAS.

The researchers then ran the algorithm on the 10 black hole binaries and divided the data into groups with similar “spectral timing features,” that is, similar delays between high-energy X-rays and reprocessed echoes. This helped to quickly track the change in X-ray echoes at every stage during a black hole’s outburst.

The team identified a common evolution across all systems. In the initial “hard” state, in which a corona and jet of high-energy particles dominates the black hole’s energy, they detected time lags that were short and fast, on the order of milliseconds. This hard state lasts for several weeks. Then, a transition occurs over several days, in which the corona and jet sputter and die out, and a soft state takes over, dominated by lower-energy X-rays from the black hole’s accretion disk.

During this hard-to-soft transition state, the team discovered that time lags grew momentarily longer in all 10 systems, implying the distance between the corona and disk also grew larger. One explanation is that the corona may briefly expand outward and upward, in a last high-energy burst before the black hole finishes the bulk of its stellar meal and goes quiet.

“We’re at the beginnings of being able to use these light echoes to reconstruct the environments closest to the black hole,” Kara says. “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.”

Reference: “The NICER “Reverberation Machine”: A Systematic Study of Time Lags in Black Hole X-Ray Binaries” by Jingyi Wang, Erin Kara, Matteo Lucchini, Adam Ingram, Michiel van der Klis, Guglielmo Mastroserio, Javier A. García, Thomas Dauser, Riley Connors, Andrew C. Fabian, James F. Steiner, Ron A. Remillard, Edward M. Cackett, Phil Uttley and Diego Altamirano, 2 May 2022, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ac6262

This research was supported, in part, by NASA.

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