Astronomers have discovered an unusual and extraordinary new space phenomenon – repeated energetic flare-ups observed over several months following the explosive death of a distant star. Led by researchers at Cornell University, a study published in November 2022 in Nature details this previously unseen activity.

The brief but bright flashes – lasting only minutes but as powerful as the original explosion 100 days later – appeared after a rare type of stellar catastrophe known as a fast blue optical transient (FBOT). Since their discovery in 2018, astronomers have speculated what could power such extreme explosions, far brighter than typical endings of massive stars but fading in days rather than weeks.

The team believes activity from the previously unknown flares, observed by 15 telescopes worldwide, confirms the engine must be a stellar corpse – a neutron star or black hole. We don’t think anything else could produce this type of flaring, says lead researcher Anna Ho. This resolves years of debate about what drives this explosion type, and reveals an unusually direct way to study newly formed stellar corpses.

In December 2022, while monitoring the fading explosion, Ho and colleagues discovered a series of five intensely bright flashes over 120 days – including one as powerful as the original blast. No one knew what to say, recalls Ho. We’d never seen anything so fast and bright months after in any supernova or FBOT. We’d never seen it at all in astronomy.

The team gathered observations from over a dozen telescopes and ruled out other light sources. Their analysis confirmed at least 14 irregular light pulses, likely just a fraction of the total number. Surprisingly, instead of steadily fading as expected, the source flared briefly and repeatedly, explains Ho. Further study may reveal processes like a black hole channeling jets of stellar material at near light speed.

Ho hopes this research will advance long-term goals of mapping how stars’ lives predict their deaths and the type of remains they leave behind. FBOTs may not be conventional supernovae, but the merger of a star and black hole. We could be witnessing a completely different channel for cosmic catastrophes, says Ho. The unusual explosions promise new insights into stellar life cycles rarely seen transitioning in a single system.

Inaccessible stellar corpses are suddenly active and observable. We believe these flares could come from one of these newly formed remains, giving us a way to study their properties when freshly made, says Ho. The discovery opens a new window into the most energetic events in the universe.


Sources

Cornell University | Ho, A.Y.Q., Perley, D.A., Chen, P. et al. Minutes-duration optical flares with supernova luminosities. Nature (2023). doi.org/10.1038/s41586-023-06673-6


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