The supermassive black holes in the heart of galaxies exert an enormous gravitational effect. What happens when a star comes too close to such a black hole has now been observed by astronomers in greater detail than ever before. They could watch a sun-like star being torn apart by the gravity of a black hole of a million solar masses and pulled apart into fine streams of matter. Around half of the star was then sucked in by the black hole, which resulted in strong bursts of rays.
At the center of most galaxies there is a supermassive black hole – also in the heart of our Milky Way. Two teams of astronomers have just received the Nobel Prize in Physics for its proof. However, while “our” black hole is rather inactive, others make themselves felt through strong bursts of radiation. These occur when the black hole sucks in matter in the form of gases or even whole stars. “When a hapless star wanders too close to a supermassive black hole in the center of a galaxy, the extreme gravitational pull of the black hole tears the star into thin threads of matter,” explains co-author Thomas Wevers of the University of Cambridge. The star is to a certain extent “spaghetted”. When some of the thin strands of star material are pulled into the black hole, a powerful surge of energy is released, which can be detected using telescopes. Astronomers refer to such an event as a Tidal Disruption Event – a rupture event caused by the tidal forces prevailing on the black hole.
Followed from the start
So far, however, scientists have rarely succeeded in discovering and observing such a rupture of a star in time. But now it has been successful. The event, baptized AT2019qiz, was registered and reported on September 29, 2019 by an automated telescope specializing in transient cosmic events. A little later, other telescopes also recorded the telltale burst of rays that glowed around 215 million light-years from Earth in the constellation Eridani. “Several sky surveys discovered the emission of the new tidal disruption event very quickly after the star was torn apart,” reports Wevers. “We immediately pointed a number of ground and space telescopes in that direction to find the source of the light.”
Over a period of six months, the team led by Wevers and first author Matt Nicholl from the University of Birmingham was able to follow the events at the distant black hole in different wave ranges of light. During this time the eruption first increased in luminosity and then faded again. The extensive observations in the ultraviolet, optical, X-ray and radio light showed for the first time the course of a tidal disruption event and the connection between the material flowing out of the star and the bright flare-up when this material is engulfed by the black hole. It is the closest such eruption to date that has been studied in such unprecedented detail, as astronomers explain.
First light up, then darken
“The observations showed that the star had roughly the same mass as our own sun and that it lost about half of it to the black hole, which is over a million times more massive,” says Nicholl. At the start of the event, the black hole’s strong gravity expands the star’s photosphere, creating strong outbursts of star material. This is snatched from the star at up to 10,000 kilometers per second. The outflow of matter combined with the increasing spaghettification of the star initially creates a bright burst of rays, which then slowly darkens again after a peak. For the first time, the astronomers were able to observe more closely why this is so: “We have found that a black hole, when it devours a star, can throw material outwards in a powerful eruption that blocks our view,” explains Nicholl’s colleague Samantha Oates. This happens because the released energy drives the debris of the star outward.
“Because we caught him early, we were actually able to watch the curtain of dust and debris build up as the black hole released a mighty spurt of material,” says co-author Kate Alexander of Northwestern University in Evanston. “This unique look behind the curtain offered the first opportunity to locate the origin of the darkening material and to follow in real time how it envelops the black hole.” The event thus helps to check the models of such tidal disruption events and that To better understand the behavior of matter in the vicinity of a supermassive black hole. According to the team, AT2019qiz could even serve as a “Rosetta Stone” for the interpretation of future observations of such tidal disruption events.
Source: Matt Nicholl (University of Birmingham) et al., Monthly Notices of the Royal Astronomical Society; doi: 10.1093 / mnras / staa2824