Falling into a supermassive black hole will leave a star mangled and destroyed but not without a fiery end. A recent study explores an intriguing case, uncovering new possibilities for stars lost to black hole bites.
Tidal Disruption Events
Invisible in light but strong in gravitational influence, some supermassive black holes reveal themselves when a star comes close enough to be ripped apart by the black hole’s tidal forces. This violent encounter produces a flare of radiation known as a tidal disruption event, allowing astronomers to explore the otherwise hidden properties of supermassive black holes and their influence on the material around them.
Tidal disruption events vary depending on the properties of the host galaxy, the supermassive black hole, and the star itself. These events often appear as X-ray flares, but over the past decade, researchers have discovered a new class of optical-ultraviolet tidal disruption events. Emitting primarily in ultraviolet and optical wavelengths, these flares are significantly less energetic than predicted, leaving researchers wondering — what drives these disruptions?
Optical and ultraviolet light curves for the two observed flares of AT 2022dbl. The flares have very similar light curves across wavelengths. Click to enlarge. [Makrygianni et al 2025]
Origins of AT 2022dbl
New detections of optical-ultraviolet tidal disruption events can provide insights into their origins, and one such discovery is particularly intriguing. AT 2022dbl first flared in 2022 and emitted a second, nearly identical flare 700 days later in 2024 — behavior uncommon among this class of tidal disruption events — raising many questions about AT 2022dbl’s origins. Did this supermassive black hole perhaps capture two unrelated stars? Is this actually the same flare seen twice due to gravitational lensing? Could a single star have survived the first flare only to be disrupted again?
Lydia Makrygianni (Lancaster University) and collaborators performed follow-up imaging and spectroscopy of AT 2022dbl to probe how the two flares compare to each other and to other observations of optical-ultraviolet tidal disruption events. With these observations and detailed analysis, the team determined that gravitational lensing, the tidal disruption of two separate stars, and even the possibility of a hidden binary companion to the supermassive black hole slurping up some stellar crumbs each cannot account for the two flares of AT 2022dbl.
Ultimately, the authors concluded that the two flares of AT 2022dbl are related to the same star, leaving two possibilities. First, loose debris from the initial flare bound to a tidal tail around the black hole could have ignited the second flare; however, the authors found that there would not be enough loose material bound to the black hole to produce the bright second flare. Rather, the second and likeliest explanation is two repeated disruptions of the same star.
Disrupting Expectations
Light curves of AT 2022dbl flares compared to other optical-ultraviolet tidal disruption events. Both flares show similar peak luminosities and decline rates to other events. Click to enlarge. [Makrygianni et al 2025]
Other optical-ultraviolet tidal disruption events appear similar to the flares of AT 2022dbl, and these have generally been assumed to be complete disruptions. With the discovery and classification of AT 2022dbl, the similar optical-ultraviolet tidal disruption events could also be partial disruptions, with their second flares on longer timescales yet to be observed. Future observations of optical-ultraviolet tidal disruption events are required to further understand the mechanisms driving them, and this study opens up new possibilities to consider.
Citation
“The Double Tidal Disruption Event AT 2022dbl Implies that at Least Some ‘Standard’ Optical Tidal Disruption Events Are Partial Disruptions,” Lydia Makrygianni et al 2025 ApJL 987 L20. doi:10.3847/2041-8213/ade155