Astronomers Observe Unprecedented Repeating Gamma-Ray Burst from Distant Galaxy

Astronomers have observed a gamma-ray burst (GRB) that repeated multiple times over a 24-hour period, a phenomenon unprecedented in the 50-year history of GRB observations. The event, designated GRB 250702B, was first detected on July 2, 2025, by NASA's Fermi Gamma-ray Space Telescope, which recorded three bursts from the same region within several hours. Subsequent analysis revealed that the source had been active nearly a day earlier, as detected by the Einstein Probe, an X-ray space telescope mission by the Chinese Academy of Sciences in collaboration with the European Space Agency and the Max Planck Institute for Extraterrestrial Physics.

Gamma-ray bursts are typically brief, lasting from milliseconds to minutes, and are usually associated with catastrophic events such as the collapse of massive stars or the merging of neutron stars. However, GRB 250702B's prolonged and repeating nature challenges existing models. Antonio Martin-Carrillo, an assistant professor in astrophysics at University College Dublin and co-lead author of a study published in The Astrophysical Journal Letters, stated that this burst is "unlike any other seen in 50 years of GRB observations."

To pinpoint the origin of the bursts, astronomers utilized the European Southern Observatory's Very Large Telescope (VLT) and its HAWK-I camera in Chile. These observations, along with data from the Hubble Space Telescope, confirmed that the source lies outside our galaxy, in a distant galaxy estimated to be a few billion light-years away. Andrew Levan, an astronomer at Radboud University in the Netherlands and co-lead author of the study, noted that the burst's duration is "100 to 1,000 times longer than most gamma-ray bursts."

The exact cause of GRB 250702B remains unknown, but researchers are considering several possibilities. One hypothesis involves an unusual type of supernova explosion that lasted much longer than typical gamma-ray-emitting supernovae. Another possibility is a white dwarf star being disrupted by an intermediate-mass black hole. Levan remarked, "If this is a massive star, it is a collapse unlike anything we have ever witnessed before."

Further observations with telescopes such as the James Webb Space Telescope are planned to refine measurements and uncover the root cause of this unprecedented event. Understanding GRB 250702B could provide new insights into the most extreme ways that stars end their lives and the mechanisms behind gamma-ray bursts.