GRB 250702BL: An unusually long & repeating gamma-ray burst | ESO
Astronomers have spotted a mysterious gamma-ray explosion, unlike any detected before. The orange dot at the center of this image is a powerful explosion that repeated several times over the course of a day, an event unlike anything ever witnessed before. The image, taken with the European Southern Observatory’s Very Large Telescope (VLT), allowed astronomers to determine that the explosion did not take place in the Milky Way but in another galaxy.
This GRB is “unlike any other seen in 50-years of GRB observations,” according to Antonio Martin-Carrillo, astronomer at University College Dublin, Ireland, and co-lead author of a study on this signal recently published in The Astrophysical Journal Letters.
GRBs are the most energetic explosions in the Universe. They are produced in catastrophic events like massive stars dying in powerful blasts or being ripped apart by black holes, among other events. They usually last milliseconds to minutes, but this signal—GRB 250702B— lasted about a day. "This is 100-1000 times longer than most GRBs,” says Andrew Levan, astronomer at Radboud University, The Netherlands, and co-lead author of the study.
“More importantly, gamma-ray bursts never repeat since the event that produces them is catastrophic,” says Martin-Carrillo. The initial alert about this GRB came on July 2 from NASA’s Fermi Gamma-ray Space Telescope. Fermi detected not one but three bursts from this source over the course of several hours. Retrospectively, it was also discovered that the source had been active almost a day earlier, as seen by the Einstein Probe, an X-ray space telescope mission by the Chinese Academy of Sciences with the European Space Agency (ESA) and the Max Planck Institute for Extraterrestrial Physics. Such a long and repeating GRB has never been seen before.
This gamma-ray burst, named GRB 250702B, was first spotted by high-energy telescopes on July 2, 2025, but its location was uncertain. The image shown here was taken on July 3 with the VLT’s HAWK-I infrared camera, which accurately pinpointed the location of the source. The explosion appeared to be nested within another galaxy, later confirmed by the NASA/European Space Agency Hubble Space Telescope.
Several scenarios have been proposed to explain this event, such as the collapse of a massive star, or a star ripped apart by a black hole. However, none can fully account for all the observed properties of these explosions unless the involved objects are rather unusual.
Release Date: Sept. 9, 2025
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