Free Astronomy Magazine September-October 2026

27 SEPTEMBER-OCTOBER 2026 ASTRO PUBLISHING likely explanation is a tidal disrup- tion event, which happens when a star strays too close to a black hole and is pulled apart by gravity. In this case, the fast rise in the optical brightness indicates an intermedi- ate-mass black hole, a long-sought class that falls between stellar-mass black holes formed by collapsing stars and the supermassive black holes found in the centers of galax- ies. These middleweight black holes have been difficult to find, and as- tronomers have been eager for new ways to identify them. AT2019ijn offers one such path: if an intermediate-mass black hole launches a jet that is not aimed di- rectly at Earth, the event may look modest at first, then become dra- matically brighter in radio light later as the jet slows and its after- glow emission spreads into view. That delayed brightening is one of the most striking features of this discovery. At 3 gigahertz, the radio signal reached a luminosity more than 100 times brighter than radio emission seen from known fast blue optical transients or supernovae at similar stages. To piece together the event, the team combined optical survey data with radio observations from the NSF VLA, including the Very Large Array Sky Survey, and additional measurements from ASKAP in Aus- tralia and the upgraded Giant Me- trewave Radio Telescope in India. That broad radio coverage let the researchers track how the signal changed over time and test models for an expanding outflow powered by a tidal disruption event. Their modeling suggests the radio emis- sion came from material moving at a significant fraction of the speed of light. The data are best explained by a narrow relativistic jet viewed from well off to the side, rather than head-on, which naturally accounts for why the radio flare appeared so late. This discovery is especially sig- nificant because it expands the way astronomers can search for hidden black holes and the extreme jets they launch. It also suggests that some unusual optical transients may be part of a broader family of black- hole-powered events that have been missed because their radio peaks arrive long after the initial flash. As new sky surveys repeatedly scan the heavens in both visible light and radio waves, astronomers expect to find more events like AT2019ijn. Each new detection could help reveal how intermedi- ate-mass black holes form, how often they tear apart stars, and under what conditions they pro- duce powerful jets. A rtist’s conception illustrating the aftermath of an intermediate- mass black hole tearing apart a pass- ing star, resulting in an accretion disk and narrow relativistic jet (top right). The dotted line indicates our line of sight from Earth. The jet’s off-axis af- terglow only became visible once the expanding radio emission (bottom left) had grown wide enough to sweep into our line of sight, causing that emission to brighten dramati- cally years after the initial event. [NSF/AUI/NSF NRAO/M.Weiss] !