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last mo.

Day-Long, Repeating Gamma-Ray Burst From Distant Galaxy Challenges Standard Models

The peer-reviewed finding has prompted intensive follow-up to determine its distance, energetics, origin.

Credit: ESO/A. Levan, A. Martin-Carrillo et al.
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The orange dot at the centre 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 ESO’s Very Large Telescope (VLT), allowed astronomers to determine that the explosion didn’t take place in the Milky Way but in another galaxy. This gamma-ray burst, named GRB 250702B, was first spotted by high-energy telescopes on 2 July, but its location was uncertain. The image shown here was taken on 3 July 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/ESA Hubble Space Telescope. Different 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. But none of them can fully account for all the observed properties of the explosion unless the involved objects are rather unusual. Credit: ESO/A. Levan, A. Martin-Carrillo et al.
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Overview

  • GRB 250702B produced multiple high-energy flares over roughly 24 hours, a duration 100 to 1,000 times longer than typical gamma-ray bursts.
  • NASA’s Fermi telescope recorded three bursts on July 2, with retrospective checks linking earlier activity seen nearly a day before by the Einstein Probe.
  • ESO’s Very Large Telescope pinpointed the fading source and Hubble confirmed an extragalactic host galaxy, likely a few billion light-years away, though the exact distance remains uncertain.
  • The team reports apparent periodicity and repetition not previously seen in GRBs, raising questions about how such an engine could operate.
  • Authors outline competing scenarios that include an unusual, long-lived stellar collapse or a tidal disruption involving a rare intermediate-mass black hole, with VLT/X-shooter and JWST data now being gathered to test these models.