💥 These black holes that burp years after eating a star

A supermassive black hole that, years after devouring a star, continues to emit intense radio waves: this is exactly what astronomers have just observed. A phenomenon comparable to a cosmic "burp," which shows that the feast of these giants is not over when visible light fades out.

Tidal disruption events (TDEs) occur when a star ventures too close to a supermassive black hole. Under the effect of extreme gravity, it is stretched into a filament of gas, a process known as "spaghettification." These events are rare, about once every 100,000 years per galaxy, which drives astronomers to monitor a large number of galaxies in hopes of catching one.


For six years, a team used the Very Large Array (VLA) in New Mexico to carry out the first systematic radio observations of dozens of TDEs. By cross-referencing this data with optical, ultraviolet archives and new X-ray surveys, they analyzed 31 well-documented TDEs. Their results, published in The Astrophysical Journal, show that late-time radio outbursts appear in two extreme situations: either the black hole swallows the gas very quickly, or its feeding rate has slowed down considerably.

In both cases, some of the gas is ejected instead of being swallowed, and it collides with the surrounding gas. This shock generates waves that accelerate particles, producing synchrotron radiation in the radio domain. This mechanism unfolds in the same way, regardless of the black hole's size, whether it is modest or millions of times more massive than the Sun, according to astrophysicists.

Furthermore, a chemical clue makes it possible to predict these late eruptions: the presence of helium lines in the early optical spectrum. This signature indicates that the stellar debris takes time to form a stable disk around the black hole, almost guaranteeing a future cosmic "burp." Astronomers estimate that the period from 2 to 6 years after discovery is the most favorable for detecting these radio signals, and that nearly 40% of TDEs generate such late emissions.

Thanks to this predictive fingerprint, researchers can now filter out quiet black holes and focus their efforts on those that promise a late show. This allows for optimized use of telescope time, a precious resource.