Astronomers have observed the brightest flare ever from a supermassive black hole, caused by it ripping apart a massive star in a distant galaxy. This tidal disruption event, nicknamed Superman, originated nearly 20 billion light years away and brightened its active galactic nucleus by over 40 times. The discovery, confirmed in 2023, sheds light on the dynamic environments around such black holes.
The flare, detected from an active galactic nucleus (AGN)—a supermassive black hole actively consuming matter—was first spotted in 2018. Initially, astronomers assumed it came from a relatively nearby galaxy due to the lack of distance measurements. However, follow-up observations in 2023 revealed its true remoteness, making it one of the most distant tidal disruption events (TDEs) ever detected.
This event intensified the AGN's brightness by more than a factor of 40, rendering it 30 times more powerful than the previous strongest flare from an AGN. Researchers, led by Matthew Graham at the California Institute of Technology, determined the cause was a massive star—at least 30 times the mass of the sun, possibly much larger—being torn apart by the black hole's gravity.
"We’ve known what AGNs are for about 60 years, and we knew that they were very variable, but we didn’t understand the variability," says Graham. "Now we have millions of AGN and we still don’t understand the variability."
The incident supports the existence of huge stars in the dense accretion disc surrounding active supermassive black holes, an environment long suspected but never directly observed. "If our interpretation is correct that this is a TDE, then it is proving the existence of these massive stars in that environment, which we have suspected," Graham adds. He describes the region as "a much more vibrant and dynamic environment" than previously thought, challenging earlier views of stable gas discs.
Studying the fading flare, which continues to emit energy, could refine models for TDEs in AGNs and help distinguish them from routine variability. "It’s really great to have something that’s not ambiguous in that way," says Vivienne Baldassare at Washington State University. "This will be really important for trying to find future TDEs and untangle different sources of variability in AGNs."
The findings appear in The Astrophysical Journal Letters (DOI: 10.3847/2041-8213/ae0b5e).