Watch an artist’s concept of a black hole shredding a star and the resulting debris hitting a second star.
- In 2019, a black hole shredded a star. The remains of the star created an expanding debris disk around the black hole.
- After a few years, the debris disk expanded into the vicinity of another star that was formerly out of reach of the black hole.
- Now the debris disk of the black hole is pummeling the star, popping off flashes in X-rays every 48 hours.
The Chandra X-Ray Observatory published this original article on October 9, 2024. Edits by EarthSky.
Black hole destroys star, goes after another
A massive black hole has torn apart one star and is now using that stellar wreckage to pummel another star or smaller black hole that used to be in the clear.
NASA’s Chandra X-ray Observatory, Hubble Space Telescope, NICER (Neutron Star Interior Composition Explorer), Neil Gehrels Swift Observatory and other telescopes made this discovery. The discovery helps astronomers link two mysteries where there had previously only been hints of a connection.
In 2019, astronomers witnessed the signal of a star that got too close to a black hole and was destroyed by the black hole’s gravitational forces. Once shredded, the star’s remains form a disk that circles around the black hole, like a type of stellar graveyard.
Over a few years, however, this disk has expanded outward and is now directly in the path of another star, or possibly a stellar-mass black hole, orbiting the massive black hole at a previously safe distance. This orbiting star is now repeatedly crashing through the debris disk, about once every 48 hours, as it circles. Chandra captured the bursts of X-rays caused by these collisions.
Black hole debris disk
Matt Nicholl of Queen’s University Belfast, United Kingdom, is the lead author of the study that appears in the current issue of Nature. The paper on the black hole – dated October 9, 2024 – is available at arXiv. Nicholl said:
Imagine a diver repeatedly going into a pool and creating a splash every time she enters the water. 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.
Quasi-periodic eruptions
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 they’ve detected only in X-rays and which 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.”
Co-author Dheeraj Pasham of the Massachusetts Institute of Technology said:
There had been feverish speculation that these phenomena were connected, and now we’ve discovered the proof that they are. It’s like getting a cosmic two-for-one in terms of solving mysteries.
Meet AT2019qiz
The Zwicky Transient Facility – a wide-field optical telescope at the Palomar Observatory – first discovered this tidal disruption event in 2019. Astronomers have now named it AT2019qiz. In 2023, astronomers used both Chandra and Hubble to study the debris left behind after the tidal disruption had ended.
Chandra obtained data during three different observations, each separated by about four to five 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.
A pause between destruction and eruption
Scientists obtained ultraviolet data from Hubble at the same time as the Chandra observations. This data allowed the scientists to determine the size of the disk around the supermassive black hole. They found 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.
Co-author Andrew Mummery of Oxford University said:
This is a big breakthrough in our understanding of the origin of these regular eruptions. 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.
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.
Bottom line: Astronomers discovered a black hole shredded one star and now, a few years later, the star’s debris disk is pummeling another star near the black hole. Every time this second star gets hit with a wave of debris, it flashes in X-ray.
Source: Quasi-periodic X-ray eruptions years after a nearby tidal disruption event
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