Astronomers have observed a spectacular cosmic phenomenon where a massive black hole is disrupting two celestial bodies, one of which was a star. The discovery, made with India’s Astrosat as well as NASA observatories including Chandra, NICER and Hubble, provides insight into the behavior of stellar debris around supermassive black holes.
History
In 2019, astronomers observed a star getting very close to a supermassive black hole. The star was torn to pieces by intense gravitational forces, known as a tidal disruption event (TDE). The remains of the star formed an accretion disk – a swirling graveyard of stellar material surrounding the black hole. For many years, this disk remained relatively stable, but recently, astronomers noticed something extraordinary. The disk expanded and began to interact with a second object, either a star or possibly a smaller black hole, previously orbiting at a safe distance.
Now, this second object is colliding with the stellar debris disk every 48 hours, producing a dramatic burst of X-rays each time it passes. “Imagine a diver entering the pool repeatedly and splashing out each time,” said Matt Nicol of Queen’s University Belfast. “Here the star is like a diver, while the disk acts as a pool, creating a cosmic ‘splash’ of gas and X-rays.”
Astronomers have long documented TDEs, where a single star is destroyed by a black hole in an intense burst of energy. However, recently, a puzzling phenomenon known as a quasi-periodic outburst (QPE) has also been observed. These are bright X-ray flares from the centers of galaxies that appear at regular intervals but were poorly understood until now.
“There was speculation that these events were linked, and now we have evidence that they are linked,” said Dheeraj Pasham of the Massachusetts Institute of Technology (MIT). It’s like solving two cosmic mysteries at once,” Mr Pasham said.
The event, now named AT2019qiz, was first identified by the Zwicky Transient Facility at the Palomar Observatory in 2019. As the accretion disk expanded and began to interact with another object, NASA’s Chandra Observatory captured three separate sets of X-ray data over several hours, providing clear evidence of repeated outbursts.
NICER, another NASA instrument on the International Space Station, continued to monitor AT2019qiz and confirmed that X-ray bursts occur every 48 hours. Complementary observations from NASA’s Swift Observatory and India’s AstroSat telescope further strengthened these findings. AstroSat’s unique ability to observe both X-ray and ultraviolet (UV) light provided important data that helped astronomers confirm the size of the accretion disk and the repeating nature of these explosions.
Co-author Gulab Dewangan of the Inter-University Center for Astronomy and Astrophysics (IUCAA) in Pune talked about the role of AstroSat. According to an ISRO report, he said, “India’s AstroSat mission provides unique UV/X-ray capability to study such phenomena.” “Astrosat’s Soft X-ray Telescope and Ultraviolet Imaging Telescope (UVIT) both detected the source AT2019qiz, but the eruptions were observed only in Will be able to make a thorough investigation of their nature.”
“This is a major breakthrough in our understanding of the origins of these regular eruptions,” said Andrew Mummery of Oxford University. “We now realize that we have to wait a few years for the explosions to ‘start’ after a star collapses because it takes some time for the disk to expand far enough to encounter another star.”