Black hole's devouring of a star seen in detail for the first time

Astronomers have for the first time seen exactly what happens when an entire star is swallowed up by a black hole.

Thanks to maths they've known in theory what should occur, but until now they had never actually seen it.

"When an unlucky star wanders too close to a supermassive black hole in the centre of a galaxy, the extreme gravitational pull of the black hole shreds the star into thin streams of material," said Thomas Wevers of the European Southern Observatory team that made the discovery

But every time it's happened before, astronomers' view of it has been obscured by dust and debris.

Last year in September, computer systems which analyse data collected by telescopes around the world sent alerts that something was going on in the sky. Astronomers quickly pointed their telescopes in the direction of the anomaly, taking place in a galaxy 215 million light-years away.

"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 kilometres a second," said NASA's Kate Alexander.

"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."

It turns out when a black hole - a mysterious object so dense nothing can escape its gravitational pull, not even light - captures a passing star, it "can launch a powerful blast of material outwards that obstructs our view", said the University of Birmingham's Samantha Oates. 

The energy released as the black hole eats up some of the star's material - in a process known as 'spaghettification' - propels the rest outwards in what scientists call a "tidal disruption event". This event, dubbed AT2019qiz, is the closest such event ever recorded.

Over the next six months astronomers watched the flare grow and subside, measuring its ultraviolet, optical, X-ray and radio waves. Half the star ended up being devoured, the rest forming the debris that usually blocks their view. 

"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 monster black hole, which is over a million times more massive," said study leader Matt Nicholl, a lecturer and Royal Astronomical Society research fellow at the University of Birmingham.

The 'tidal disruption event' in action.
The 'tidal disruption event' in action (animated). Photo credit: Supplied

Physics equations developed by Albert Einstein, which have been proven time and time again to work wherever they're applied, break down when you get to the centre of a black hole. The astronomers say what they've learned from AT2019qiz, and future tidal disruptions they expect to find with the under-construction Extremely Large Telescope in Chile, could "solve further mysteries of black hole physics".

The full study, An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz, can be read in journal Monthly Notices of the Royal Astronomical Society. The scientists also released an animation of how it might have looked close-up.