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Astronomers unveil a mind-blowing revelation about black holes: they regurgitate stars years after consumption! Dive into the astonishing findings that challenge everything we thought we knew about these cosmic giants.
Astronomers have recently made a remarkable discovery regarding black holes that consume stars. After years of observing black holes engaged in tidal disruption events (TDEs), they found that up to 50% of these black holes “regurgitate” the remains of the stars they devoured years later.
TDEs occur when stars stray too close to black holes. The immense gravitational forces exerted by these cosmic behemoths cause extreme stretching and squeezing of the stars, a process known as “spaghettification.” During TDEs, unfortunate stars are rapidly torn apart or “unravelled,” leading to a powerful burst of electromagnetic radiation in visible light.
When a star is destroyed, some of its material is flung away from the black hole, while the rest forms a thin, disk-like structure called an accretion disk, which gradually feeds the material to the black hole. Initially, the accretion disk is unstable, resulting in chaotic matter movement and collisions that produce detectable radio wave outflows. Traditionally, astronomers only monitored these star-consuming black holes for a few months following TDEs.
However, in this new research, astronomers extended their observations of black holes involved in TDEs to hundreds of days and made a surprising discovery. In up to 50% of cases, these black holes emitted stellar material years after the TDE events, a phenomenon described as a “burp.” Yvette Cendes, the lead author of the study and a research associate at the Harvard and Smithsonian Center for Astrophysics, likened this phenomenon to a delayed release of material from the accretion disk, defying previous expectations.
Among the 24 black holes studied, 10 of them exhibited this re-emission of material between two and six years after the initial star destruction events. These findings are detailed in a study uploaded to the preprint database arXiv on August 25, 2023, which has not yet undergone peer review.
The precise cause of these black holes “switching on” after many years remains unknown, but it is confirmed that the source is not within the black holes themselves. Black holes are characterized by their event horizon, the point beyond which even light cannot escape.
As Cendes explained, “Black holes are very extreme gravitational environments even before you pass that event horizon, and that’s what’s really driving this. We don’t know if the material seen in radio waves is from the accretion disk or is being stored somewhere closer to the black hole. But black holes are obviously messy eaters.”
This discovery has raised questions about existing computer models that simulate TDEs, which typically terminate shortly after the star’s destruction. The research suggests that these models need to be updated to account for the unexpected behaviour of these black holes.
For example, in two cases, black holes emitted radio waves that initially peaked, faded, and then peaked again. This secondary peak was entirely unexpected and challenged previous assumptions that TDEs produce a single outflow of material.
Cendes and her team plan to continue monitoring all the black holes responsible for TDEs, especially those that are still increasing in brightness, to further unravel the mysteries of these celestial phenomena.