in Dora Bruder, by Patrick Modiano
One of the most exciting opportunities offered by Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) is the discovery of tidal disruption events (TDEs). These events occur when a black hole disrupts an unfortunate star, releasing an enormous burst of energy that fades over timescales ranging from days to years, depending on the mass of the disrupting black hole.
Almost 100 of these events have been discovered in the Zwicky Transient Facility, with LSST poised to uncover many more when the full survey commences. Short-lived tidal disruption events are thought to be observational evidence for the missing population of intermediate mass black holes, thought to be the building blocks of the supermassive black holes residing at the centers of galaxies. However, they are incredibly challenging to discover, and the majority of tidal disruption events are from central supermassive black holes.
During the 8th COIN residence program, we uncovered an unusual event, AT2022zod, residing in an elliptical galaxy at redshift 0.11. This energetic event only had a total duration of around 30 days, and is slightly off-nuclear from the galaxy center. We delved into the host galaxy environment and found it to be a retired galaxy with a central supermassive black hole of 10^8 solar masses. However, AT2022zod is very unlikely to be the result of the host galaxy’s central supermassive black hole–it is far too short in duration. Lightcurve modeling of AT2022zod suggests that the event is caused by an intermediate mass black hole. As we know this black hole is surrounded by a star cluster, we suggest that AT2022zod is the stripped nucleus of a dwarf galaxy that was acquired by the host galaxy earlier in its evolution–the most distant candidate system to date.
One important thing to note about AT2022zod is that it went entirely unclassified in the alerts stream, meaning that our current techniques to search for tidal disruption events may be missing an important population of candidate intermediate mass black holes. This problem will only be exacerbated in the LSST-era, when we go from 300 k of alerts per night to 10 million alerts per night. Therefore, systems like AT2022zod are crucial for understanding how to effectively find our missing population of intermediate mass black holes.