A black hole’s destructive power unfolds as scientists discover a stellar collision in a galaxy’s core. A torn-apart star forms a debris disk that encounters a second star, triggering repeating X-ray bursts. This dramatic encounter, witnessed by multiple observatories, has linked two cosmic mysteries, providing clues about quasi-periodic eruptions and tidal disruption events.
A massive black hole has torn apart a star, scattering its remnants into a disk of debris that now threatens another nearby object—possibly another star or a smaller black hole that was previously safe.
This discovery, made through observations with NASA’s Chandra X-ray Observatory, Hubble Space Telescope, NICER (Neutron Star Interior Composition Explorer), Neil Gehrels Swift Observatory, and other telescopes, has provided crucial evidence connecting two previously mysterious phenomena.
The Formation of a Stellar Graveyard
In 2019, astronomers detected the signal of a star that had ventured too close to a black hole, where it was torn apart by intense gravitational forces. Its remains formed a swirling disk around the black hole—a kind of “stellar graveyard.”
Over the past few years, this debris disk has expanded outward and now lies in the orbit of another celestial object that circles the black hole at a once-safe distance. This object now plunges through the debris every 48 hours, producing bursts of X-rays with each collision—a phenomenon captured by Chandra and offering astronomers a rare view into the violent interactions around black holes.
“Imagine a diver repeatedly going into a pool and creating a splash every time she enters the water,” said Matt Nicholl of Queen’s University Belfast, United Kingdom, the lead author of the study that appears in the current issue of Nature. “The star in this comparison is like the diver and the disk is the pool, and each time the star strikes the surface it creates a huge ‘splash’ of gas and X-rays. As the star orbits around the black hole, it does this over and over again.”
Tidal Disruption Events and X-ray Bursts
Scientists have documented many cases where an object gets too close to a black hole and gets torn apart in a single burst of light. Astronomers call these “tidal disruption events.” In recent years, astronomers have also discovered a new class of bright flashes from the centers of galaxies, which are detected only in X-rays and repeat many times. These events are also connected to supermassive black holes, but astronomers could not explain what caused the semi-regular bursts of X-rays. They dubbed these “quasi-periodic eruptions.”
“There had been feverish speculation that these phenomena were connected, and now we’ve discovered the proof that they are,” said co-author Dheeraj Pasham of the Massachusetts Institute of Technology. “It’s like getting a cosmic two-for-one in terms of solving mysteries.”
AT2019qiz: Unraveling the Mystery
This tidal disruption event now known as AT2019qiz was first discovered by a wide-field optical telescope at the Palomar Observatory, called the Zwicky Transient Facility, in 2019. In 2023, astronomers used both Chandra and Hubble to study the debris left behind after the tidal disruption had ended.
The Chandra data was obtained during three different observations, each separated by about 4 to 5 hours. The total exposure of about 14 hours of Chandra time revealed only a weak signal in the first and last chunk, but a very strong signal in the middle observation.
From there Nicholl and his colleagues used NICER to look frequently at AT2019qiz for repeated X-ray bursts. The NICER data showed that AT2019qiz erupts roughly every 48 hours. Observations from Swift and India’s AstroSat telescope cemented the finding.
Revealing the Disk’s Size and Impact
The ultraviolet data from Hubble, obtained at the same time as the Chandra observations, allowed the scientists to determine the size of the disk around the supermassive black hole. They found that the disk had become large enough that if any object was orbiting the black hole with a period of about a week or less, it would collide with the disk and cause eruptions.
“This is a big breakthrough in our understanding of the origin of these regular eruptions,” said Andrew Mummery of Oxford University. “We now realize we need to wait a few years for the eruptions to ‘turn on’ after a star has been torn apart because it takes some time for the disk to spread out far enough to encounter another star.”
Implications for Future Astronomical Research
This result has implications for searching for more quasi-periodic eruptions associated with tidal disruptions. Finding more of these would allow astronomers to measure the prevalence and distances of objects in close orbits around supermassive black holes. Some of these may be excellent targets for the planned future gravitational wave observatories. NASA’s missions are part of a growing, worldwide network of missions with different but complementary capabilities, watching for changes like these to solve mysteries of how the universe works.
The paper describing these results was first published online by Nature on October 9, 2024. It also appeared in print in the October 24 issue of the journal.
Reference: “Quasi-periodic X-ray eruptions years after a nearby tidal disruption event” by M. Nicholl, D. R. Pasham, A. Mummery, M. Guolo, K. Gendreau, G. C. Dewangan, E. C. Ferrara, R. Remillard, C. Bonnerot, J. Chakraborty, A. Hajela, V. S. Dhillon, A. F. Gillan, J. Greenwood, M. E. Huber, A. Janiuk, G. Salvesen, S. van Velzen, A. Aamer, K. D. Alexander, C. R. Angus, Z. Arzoumanian, K. Auchettl, E. Berger, T. de Boer, Y. Cendes, K. C. Chambers, T.-W. Chen, R. Chornock, M. D. Fulton, H. Gao, J. H. Gillanders, S. Gomez, B. P. Gompertz, A. C. Fabian, J. Herman, A. Ingram, E. Kara, T. Laskar, A. Lawrence, C.-C. Lin, T. B. Lowe, E. A. Magnier, R. Margutti, S. L. McGee, P. Minguez, T. Moore, E. Nathan, S. R. Oates, K. C. Patra, P. Ramsden, V. Ravi, E. J. Ridley, X. Sheng, S. J. Smartt, K. W. Smith, S. Srivastav, R. Stein, H. F. Stevance, S. G. D. Turner, R. J. Wainscoat, J. Weston, T. Wevers and D. R. Young, 9 October 2024, Nature.
DOI: 10.1038/s41586-024-08023-6
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
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