It is a rare image that could have come out of a science fiction book: an “unlucky” star wanders too close to a supermassive black hole and ends up sucked in like spaghetti causing a monumental explosion of light. The phenomenon, known as tidal disruption event, was recently captured by the European Southern Observatory (ESO) telescopes and studied with an unprecedented detail. It is the closest such flare recorded to date at just over 215 million light-years from Earth.
An article based on this discovery, titled “An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz”, was published this Monday, October 12, in Monthly Notices of the Royal Astronomical Society, one of the world’s leading astronomy journals. Santiago Gonzalez, researcher at CENTRA/IST, is part of the research team.
According to the Técnico researcher, this work is about one of the most impressive behaviours of black holes. “When an unlucky star wanders too close to a supermassive black hole, the extreme gravitational pull of the black hole shreds the star into thin streams of material, resulting in a phenomenon known as spaghettification. When this happens, the remains of the star are swallowed by the black hole, which is a million times more massive. During this spaghettification process, a bright flare of energy is released, which astronomers can detect at an early stage of the event”.
These tidal disruption events are rare and not always easy to study. The team, led by Matt Nicholl (University of Birmingham, United Kingdom) and involving more than 40 researchers from around the world, used ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT), to observe a new flash of light that occurred last year close to a supermassive black hole, to investigate in detail what happens when a star is devoured by such a monster.
As some of the thin strands of stellar material fall into the black hole during this spaghettification process, a bright flare of energy is released, which astronomers can detect. Although powerful and bright, up to now astronomers have had trouble investigating this burst of light, which is often obscured by a curtain of dust and debris. Now, astronomers have been able to shed light on the origin of this curtain: when a black hole devours a star, it can launch a powerful blast of material outwards that obstructs view. This happens because the energy released as the black hole eats up stellar material propels the star’s debris outwards.
Observing the bright flare from the beginning
The discovery was possible because the tidal disruption event the team studied, AT2019qiz, was found just a short time after the star was ripped apart. “Observations in optical, ultravioleta and X-ray allowed us to capture this phenomenon from the beginning” says Santiago Gonzalez.
Caughting the event early allowed the researchers to 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, and provided the first opportunity to pinpoint the origin of the obscuring material and follow in real time how it engulfs the black hole.
The team carried out observations of AT2019qiz, located in a spiral galaxy in the constellation of Eridanus, over a 6-month period as the flare grew in luminosity and then faded away. Several sky surveys discovered emission from the new tidal disruption event very quickly after the star was ripped apart,
Multiple observations of the event were taken over the following months with facilities that included X-shooter and EFOSC2, powerful instruments on ESO’s VLT and ESO’s NTT. The prompt and extensive observations in ultraviolet, optical, X-ray and radio 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. The observations showed that the star had approximately 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
The research helps us better understand supermassive black holes and how matter behaves in the extreme gravity environments around them. According to the team, AT2019qiz could even act as a ‘Rosetta stone’ for interpreting future observations of tidal disruption events. ESO’s Extremely Large Telescope (ELT), planned to start operating this decade, will enable researchers to detect increasingly fainter and faster evolving tidal disruption events, to solve further mysteries of black hole physics.
Santiago Gonzalez’s work has contributed to the observation of events of this type as part of the ePESSTO + collaboration, using the EFOSC2 instrument at the NTT telescope in Chile. “It is amazing to see that theoretical predictions are proven in a lot more detail and that we can explore and understand the richness of nature,” says the Técnico researcher.
