The eROSITA X-ray telescope has captured a rare astronomical event. Astronomers observed the galaxy HE 1237−2252 undergo dramatic changes in brightness over just 18 months, with its X-ray output dropping by a factor of 17 before surging back to normal levels.
HE 1237−2252 hosts a "changing-look" active galactic nucleus, a phenomenon where the supermassive black hole at a galaxy's center appears to switch off and then rapidly reignite. The dimming and recovery occurred far faster than typical for such events, making this observation unusual and valuable for understanding black hole behavior.
Active galactic nuclei powered by supermassive black holes emit intense radiation across the electromagnetic spectrum. When material spirals into these black holes, it heats to extreme temperatures and radiates energy, particularly in X-rays. The dramatic flux change in HE 1237−2252 suggests the accretion flow around its black hole fundamentally shifted, either through a change in the rate of material falling in or alterations in how that material emits radiation.
Changing-look AGN have been identified before, but rapid transitions like this remain rare. The eROSITA instrument, which launched in 2019 aboard the Spektrum-Röentgen-Gamma satellite, provides all-sky surveys that catch these transient events. Its sensitivity allows astronomers to track X-ray sources systematically across the entire sky, increasing the odds of detecting short-timescale variations.
The research team uploaded their analysis to the arXiv preprint server on May 8, where it awaits peer review. Their findings advance understanding of how supermassive black holes regulate their feeding behavior. The 18-month timescale offers constraints on physical processes governing accretion, whether related to instabilities in the acc