The cosmic violence of a black hole tearing apart a star produced a brilliant burst of radio light, which has been observed by astronomers thanks to a new international collaboration.
The U.S. National Science Foundation’s Very Large Array (NSF VLA) captured an off-axis afterglow that the researchers believe was left behind by a powerful jet produced by the star’s destruction. The black hole event was dubbed AT2019ijn by the Chinese research team that made the observation using U.S. equipment, and was described in a recent paper published in The Astrophysical Journal Letters.
Intriguingly, this explosive cosmic event provides astronomers with important new clues in the search for some of the universe’s rarest types of black holes.
A Bright Blue Flash
Various optical surveys of the cosmos detected the bright blue flash of AT2019ijn. For a few days, it continued to grow in brilliance before oddly fading at a rate far slower than is typical of similar transients.
Yet the optical spectrum did not tell the full story. As researchers combed through radio observations, they unexpectedly discovered that the radio emission did not peak within mere days but continued growing for two years before decaying over the next four. Also notable was the intensity of the emission, which was far more luminous than is typically seen during these phases of a stellar explosion.
Its 3-gigahertz luminosity was more than 100 times greater than signals typically observed from supernovae or fast blue optical transients.
Understanding the event required researchers to combine optical data with radio observations from the NSF VLA, India’s Giant Metrewave Radio Telescope, and Australia’s ASKAP. By expanding their radio view with these various facilities, the researchers were able to observe how the event changed over time, allowing them to develop and test various models.
A Black Hole Explanation
The Chinese astronomers identified a black hole as the most likely cause of these strange observations. Their focus was on a tidal disruption event, which occurs when a star wanders too close to a black hole and is torn apart by the incredibly powerful gravitational forces it encounters. Intriguingly, the researchers found that an event matching the observed optical brightness would require an extremely rare class of black hole.
Black holes are among the most extreme objects in the universe and tend to occupy opposite ends of a mass spectrum. The smaller variety is known as a “stellar-mass” black hole, since these objects form from the collapse of stars. At the other end are supermassive black holes, which anchor entire galaxies. However, intermediate-mass black holes have largely eluded astronomers, partly because their presence can be difficult to detect.
Detecting Intermediate-Mass Black Holes
Crucially, AT2019ijn allowed researchers to identify a new avenue for detecting these rare black holes.
Perspective is important in these detections. When an intermediate-mass black hole’s jet is not aimed directly toward Earth, the event may appear far less intense at optical wavelengths than expected. However, continued observation at radio wavelengths can reveal a much more intense afterglow as the jet evolves. This delayed brightening could therefore provide an important new clue for identifying potential intermediate-mass black holes.
Looking more broadly, the astronomers contend that many extreme black hole events may be missed because observations cease after the initial optical flash, leaving potentially intense radio peaks unobserved. As even more advanced observational platforms come online, such as the upcoming Next Generation Very Large Array, future radio surveys may reveal more such events, potentially illuminating a previously unrecognized class of transients similar to AT2019ijn.
The paper, “AT2019ijn: A Fast-rising, Slow-decaying Blue Optical Transient with Exceptionally Bright Radio Emission,” appeared in Astrophysical Journal Letters on July 6, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.