From the heart of a galaxy 215 million light-years away, a brilliant flash of light flickered into the void of space – the last cry of light from a dying star that came too close and was pulled apart by a supermassive black hole.
It is the next such star death that we have ever observed, and it offers unprecedented insight into the violent cosmic process.
While it is unusual to catch a star death by a black hole, astronomers have watched enough by now to find out how it happens. When a star ventures too close, the black hole's immense tidal force – the product of its gravitational field – first expands and then pulls the star so tight that it is torn apart.
This tidal disruption event (TDE) releases a brilliant light before the debris from the crumbling star disappears behind the black hole's event horizon. But this flare of light is often at least partially obscured by a cloud of dust, making it difficult to study the finer details.
The new TDE, which was first discovered last September and bears the name AT2019qiz, is now helping a team led by astronomer Matt Nicholl from the University of Birmingham in Great Britain to shed light on the origin of this dust.
"We have found that when a black hole engulfs a star, it can cause a powerful outward explosion of material that obstructs our view," said astronomer Samantha Oates of the University of Birmingham in the UK.
Stellar TDEs are one of those cosmic phenomena that cannot be predicted. All you have to do is keep gazing at the sky and wait for the tell-tale flicker. It did so with AT2019qiz, and astronomers quickly turned their telescopes into a small patch of sky in the constellation Eridanus and the heart of a spiral galaxy 215 million light years away.
"Several sky surveys showed emissions from the new tidal disruption event very quickly after the star was torn apart," said astronomer Thomas Wevers, who was at Cambridge University in the UK while doing the research.
"We immediately pointed a number of ground and space telescopes in that direction to see how the light was created."
As the star is torn apart, some of the resulting debris spaghettifies and weakens into a long, thin thread of material that flows into the black hole.
The torch is the result of intense gravitational and frictional influences in this accretive material. These influences heat the material to such high temperatures that the TDE can briefly outshine the host galaxy.
From that first flare-up, the TDE will fade over a period of months. Nicholl and his team carefully observed and plotted the fading of AT2019qiz over multiple wavelengths of light, including ultraviolet, radio, optics, and x-rays. This was another stroke of luck – TDEs usually glow optically and ultraviolet.
This light enabled the team to calculate the masses involved in the AT2019qiz.
"The observations showed that the star was roughly the same mass as our own sun and that it lost roughly half of that to the black hole, which is over a million times more massive," said Nicholl.
Between the quickness with which the team focused their attention on the event, its proximity and the broader spectrum over which they observed it, they also found that the dark dust was an integral part of the TDE and not a separate phenomenon.
"AT2019qiz is the next tidal disturbance event detected to date and is therefore incredibly observable across the electromagnetic spectrum. This is the first time we have seen direct evidence of outflowing gas during the disturbance and accretion process, both optical and optical explain radio emissions we've seen in the past, "said astronomer Edo Berger of the Harvard-Smithsonian Center for Astrophysics.
"So far, the nature of these emissions has been hotly debated, but here we see that the two regimes are linked by a single process. This event teaches us the detailed physical processes of accretion and mass ejection from supermassive black holes."
The research is just the latest breakthrough in studying TDEs.
Earlier this year, a team confirmed that some of the debris from the destroyed star is swirling into a disk of material that flows like water in a drain into the black hole. A TDE a few years earlier found that the jet of plasma ejected by the black hole is proportional to the amount of star it is engulfing. And a star that has escaped total disruption shows that a black hole can ration its meal and feed on an orbiting companion for billions of years.
But AT2019qiz, the researchers say, is a special case that will continue to support our efforts to understand these incredible events.
"The exquisite data presented here," they wrote in their article, "make AT2019qiz a Rosetta Stone for interpreting future TDE observations in the age of large samples from the Zwicky Transient Facility, the Rubin Observatory, and other new and ongoing time domain studies to be expected." . "
The research was published in the Royal Astronomical Society's monthly bulletins.