Rare explosion of black hole-torn star light detected



Observation of the explosion was possible with telescopes from the European Southern Observatory and other organisations

An international team of astronomers has detected a rare burst of light from a star torn apart by a supermassive black hole, a phenomenon known as "tidal disruption" and the closest observed so far.

Observation was made possible by telescopes from the European Southern Observatory (ESO) and other organizations around the world and the event happened just over 215 million light-years from Earth.

"The idea of a black hole 'sucking' a nearby star sounds like science fiction. But that's exactly what happens at a tidal disruption event," said Matt Nicholl, professor and researcher at the Royal Astronomical Society at the University of Birmingham, UK, and lead author of the new study.

The ESO stated in a statement that these tidal disruption events, where a star experiences what is known as spaghetti when absorbed by a black hole, "are rare and not always easy to study".

In order to study in detail what happens when a star is devoured by such a monster, the research team pointed to ESO's VLT (Very Large Telescope) and NTT (New Technology Telescope) towards a new flash of light that took place last year near a supermassive black hole.

In theory astronomers know what should happen in such a situation; according to Thomas Wevers, another of the researchers who participated in the observation, "when an unfortunate star roams too close to a supermassive black hole in the center of a galaxy, the extreme gravitational pull of the black hole tears the star, ripping thin streams of material at it."

As some of the fine strands of stellar matter fall into the black hole during this process, called spaghettiification, a brilliant round of energy is released that astronomers can detect.

Although powerful and bright, so far astronomers have struggled to investigate these bursts of light that are often obscured by a curtain of dust and debris: they have now been able to shed light on the origin of this curtain.

"We found that when a black hole devours a star, it can throw a powerful explosion of matter outwards that obstructs our view," explains Samantha Oates of the University of Birmingham.

He adds that this happens because the energy released when the black hole feeds on the stellar material drives the star's debris outwards.

The discovery was possible because the tidal disruption event the team studied, AT2019qiz, was detected shortly after the star was shattered.

"Actually, because we detected it early, we were able to see the curtain of dust and debris forming as the black hole launched a powerful jet of material with speeds of up to 10,000 kilometers per second," explains Kate Alexander, a postdoctoral researcher (NASA Einstein Fellow) at Northwestern University in the United States.

"This 'look behind the curtain' was our first opportunity to identify the origin of the darkening material and follow in real time how it wraps around the black hole," Alexander adds.

Over a period of 6 months, during which the call grew in luminosity and then faded, the team made observations of AT2019qiz, located in a spiral galaxy, in the constellation Eridanus.

"Several probes detected the emission of the new tidal disruption event very soon after the star was shattered," says Wevers, indicating that they immediately targeted the set of terrestrial and space telescopes in that direction to see how light was produced.

In the following months, multiple observations of the event were made with other facilities; haste and extensive observations in ultraviolet light, optical range, X-rays and radio waves, revealed, for the first time, a direct connection between the material flowing from the star and the bright flash emitted as it is devoured by the black hole.

"The observations showed that the star had about the same mass as our own Sun and that the monstrous black hole, which is more than a million times more massive, had made it lose about half of that mass," according to Nicholl.

The astronomer team believes AT2019qiz could even act as a "Rosetta stone" to interpret future observations of tidal disruption events.

On the other hand, ESO's ELT (Extremely Large Telescope), which is expected to start operations for this decade, will allow researchers to detect ever weaker and faster-evolving tidal disruption events in order to solve more mysteries of black hole physics.