A star in the act of being devoured by a supermassive black hole. It’s the latest incredible cosmic phenomenon tracked and traced by astronomers using giant telescopes.
This iconic “tidal disruption event”—named “AT2019qiz”—occurred 215 million light-years away, which makes it the closest observed so far.
“The idea of a black hole “sucking in” a nearby star sounds like science fiction, but this is exactly what happens in a tidal disruption event,” said Dr Matt Nicholl, a lecturer and Royal Astronomical Society research fellow at the University of Birmingham in the UK, and lead author of the paper published today in Monthly Notices of the Royal Astronomical Society.
“We were able to investigate in detail what happens when a star is eaten by such a monster,” he added.
What is a ‘tidal disruption event?’
It’s when a star gets too close to a black hole and thus gets pulled apart by the black hole’s extreme gravitational pull. “An unfortunate star in the nucleus of a galaxy can find itself on an orbit that intersects the tidal radius of the central supermassive black hole,” reads the paper. “This destruction can power a very luminous flare.” That’s exactly what the researchers saw.
What happened to the star?
It was shredded into a tube of material. The astronomical term used to describe it is “spaghettification.”
Under the extreme tidal forces of a black hole, stars can be vertically stretched and horizontally compressed into long thin streams of material. “The observations showed that the star had roughly the same mass as our own Sun, and that it lost about half of that to the black hole, which is over a million times more massive,” said Nicholl, who is also a visiting researcher at the University of Edinburgh in the UK.
Why is this such a rare sight for astronomers?
During the star’s “spaghettification” some of the material fell into the black hole and released a bright flare of energy. Astronomers detected that rare blast of light. It’s a sight described by the researchers as “faint and fast”—such events are usually obscured by a curtain of dust and debris, and it was only because it was detected just after the star was ripped apart that the flare could be detected.
“When a black hole devours a star, it can launch a powerful blast of material outwards that obstructs our view,” said Samantha Oates at the University of Birmingham. “This happens because the energy released as the black hole eats up stellar material propels the star’s debris outwards.”
How did astronomers find this ‘tidal disruption event?’
“Several sky surveys discovered emission from the new tidal disruption event very quickly after the star was ripped apart,” said Thomas Wevers, an ESO Fellow in Santiago, Chile, who was at the Institute of Astronomy, University of Cambridge, UK, when he conducted the work. “
We immediately pointed a suite of ground-based and space telescopes in that direction to see how the light was produced,” he added.
How did astronomers capture this rare event?
An international team of scientists led by the University of Birmingham used the European Southern Observatory’s Very Large Telescope and New Technology Telescope, the Las Cumbres Observatory global telescope network, and the Neil Gehrel’s Swift Satellite to make prompt and extensive optical, ultra-violet and X-ray observations of the flare for six months as it grew brighter and then faded away.
That light revealed, for the first time, a direct connection between the material flowing out from the star and the bright flare emitted as it is devoured by the black hole.
“Because we caught it early we could actually see the curtain of dust and debris being drawn up as the black hole launched a powerful outflow of material with velocities up to 10,000 km/s,” said Kate Alexander, NASA Einstein Fellow at Northwestern University in the US.
“This unique “peek behind the curtain” provided the first opportunity to pinpoint the origin of the obscuring material and follow in real time how it engulfs the black hole,” she added.
Where in the night sky did the ‘tidal disruption event’ happen?
The incredible event happened in a face-on spiral galaxy in the direction of the constellation of Eridanus, “the river,” though that area of the night sky is also very close to the bright blue star Rigel in the constellation of Orion.
What happens next?
“Given the proximity of AT2019qiz, this galaxy is an ideal candidate for the Hubble Space Telescope or adaptive optics imaging to resolve the structure of the nucleus,” reads the paper. Adaptive optics use lasers to correct for the turbulence of Earth’s atmosphere and so make it possible for ground-based telescopes to produce images as sharp and as clear as space-based telescopes.
It’s also hoped that the ESO’s Extremely Large Telescope (ELT)—whose 39.3-meter-diameter mirror will make it the world’s largest optical/near-infrared telescope—will enable researchers to detect increasingly fainter and faster tidal disruption events as they evolve. It’s planned to start operating before 2030.
It’s thought that AT2019qiz could act as a “Rosetta Stone” for interpreting observations of tidal disruption events in the future.
Wishing you clear skies and wide eyes.