A huge black hole has ripped apart one star and is now using the stellar wreckage to destroy another star or smaller black hole that was previously unaffected. This discovery, made with NASA’s Chandra X-ray Observatory, Hubble Space Telescope, Neutron Star Interior Composition Explorer (NICER), Neil Gehrels Swift Observatory, and other telescopes, allows astronomers to connect two mysteries that were previously only hinted at.
Image Credit: X-ray: NASA/CXC/Queen's Univ. Belfast/M. Nicholl et al.; Optical/IR: PanSTARRS, NSF/Legacy Survey/SDSS; Illustration: Soheb Mandhai / The Astro Phoenix; Image Processing: NASA/CXC/SAO/N. Wolk
In 2019, astronomers observed the signal of a star that became too close to a black hole and was destroyed by its gravitational forces. Once shredded, the star’s remains form a disk that circles the black hole, resembling a stellar graveyard.
Over the course of a few years, however, this disk has expanded outward. It is now directly in the path of another star, or possibly a stellar-mass black hole, orbiting the massive black hole at previously safe distances. As it circles, this orbiting star is now crashing through the debris disk approximately once every 48 hours. When it does, the collision produces bursts of X-rays, which astronomers captured using Chandra.
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.
Matt Nicholl, Study Lead Author, School of Mathematics and Physics, Queen’s University Belfast
Scientists have documented numerous instances when an object comes too close to a black hole and is ripped apart in a single burst of light. Astronomers refer to these as “tidal disruption events.”
Astronomers have recently discovered a new class of bright flashes from galaxies’ centers that can only be detected in X-rays and occur repeatedly. These events are also linked to supermassive black holes, but astronomers cannot explain what caused the semi-regular bursts of X-rays. They called them “quasi-periodic eruptions.”
There had been feverish speculation that these phenomena were connected, and now we have discovered the proof that they are. It is like getting a cosmic two-for-one in terms of solving mysteries.
Dheeraj Pasham, Study Co-Author, Massachusetts Institute of Technology
The Zwicky Transient Facility, a wide-field optical telescope at the Palomar Observatory, made the initial discovery of this tidal disruption event, known as AT2019qiz, in 2019. In 2023, astronomers examined the debris left behind after the tidal disruption ended using Chandra and Hubble.
The Chandra data was collected using three separate observations, separated by roughly four to five hours. Only a weak signal was detected in the first and last chunks of the approximately 14-hour Chandra time exposure, but a very strong signal was detected in the middle observation.
After that, Nicholl and his associates regularly checked AT2019qiz using NICER for recurring X-ray bursts. According to the NICER data, AT2019qiz erupts approximately every 48 hours. India’s AstroSat telescope and Swift observations confirmed the discovery.
The scientists ascertained the size of the disk surrounding the supermassive black hole using the ultraviolet data from Hubble, which was acquired concurrently with the Chandra observations. They discovered that the disk had grown to such a size that any object orbiting the black hole for less than a week would collide with it and trigger eruptions.
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.
Andrew Mummery, Leverhulme-Peierls Fellow, Oxford University
This finding has implications for the search for more quasi-periodic eruptions caused by tidal disruptions. Finding more of these would allow astronomers to determine the number and distance of objects in close orbit around supermassive black holes.
Some of these may make outstanding targets for future gravitational wave observatories. NASA's missions are part of a growing global network of missions with diverse but complementary capabilities, monitoring for changes like these to help solve mysteries about how the universe works.