On December 11, 2021, NASA’s Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory discovered a burst of high-energy light coming from the edge of a galaxy around 1 billion light-years away. The occurrence has challenged scientists’ perceptions of gamma-ray bursts (GRBs), the most potent phenomena in the cosmos.
The burst GRB 211211A was the first long-duration gamma-ray burst traced to a neutron star merger origin. Considered a paradigm-shifting, the eruption lasted about a minute, and our follow-up observations led to the identification of a kilonova.
Eleonora Troja, an astrophysicist at the University of Rome who led another team that studied the burst, said, “Many years ago, Neil Gehrels, an astrophysicist and Swift’s namesake, suggested that neutron star mergers could produce some long bursts. The kilonova we observed is the proof that connects mergers to these long-duration events, forcing us to rethink how black holes are formed.”
Alessio Mei, a doctoral candidate at the Gran Sasso Science Institute in L’Aquila, Italy, who led a group that studied the data, said, “This is the first time we’ve seen such an excess of high-energy gamma rays in the afterglow of a merger event. Normally that emission decreases over time. It’s possible these high-energy gamma rays come from collisions between visible light from the kilonova and electrons in particle jets. The jets could be weakening from the original explosion or new ones powered by the resulting black hole or magnetar.”
The heavy elements in the cosmos are believed by scientists to have been produced by neutron star mergers. They based their calculations on the frequency of brief bursts believed to occur across the cosmos. Now they’ll need to consider extended bursts into their calculations as well.
Regina Caputo, Swift project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said, “This result underscores the importance of our missions working together and with others to provide multiwavelength follow-up of these kinds of phenomenon. Similar coordinated efforts have hinted that some supernovae might produce short bursts, but this event is the final nail in the coffin for the simple dichotomy we’ve used for years. You never know when you might find something surprising.”
- Rastinejad, J.C., Gompertz, B.P., Levan, A.J. et al. A kilonova following a long-duration gamma-ray burst at 350 Mpc. Nature 612, 223–227 (2022). DOI: 10.1038/s41586-022-05390-w
- Troja, E., Fryer, C.L., O’Connor, B., et al. A nearby long gamma-ray burst from a merger of compact objects. Nature 612, 228–231 (2022). DOI: 10.1038/s41586-022-05327-3
- Mei, A., Banerjee, B., Oganesyan, G. et al. Gigaelectronvolt emission from a compact binary merger. Nature 612, 236–239 (2022). DOI: 10.1038/s41586-022-05404-7
- Gompertz, B.P., Ravasio, M.E., Nicholl, M. et al. The case for a minute-long merger-driven gamma-ray burst from fast-cooling synchrotron emission. Nat Astron (2022). DOI: 10.1038/s41550-022-01819-4