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2d ago

Day-Long, Repeating Gamma-Ray Burst From Distant Galaxy Upends GRB Theory

Coordinated multi‑wavelength observations confirm an extragalactic origin.

Credit: ESO/A. Levan, A. Martin-Carrillo et al.
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.
Image

Overview

  • NASA’s Fermi telescope recorded multiple high‑energy flares from GRB 250702B over several hours on July 2, 2025, and the Einstein Probe later found the same source active nearly a day earlier in soft X‑rays.
  • Follow‑up imaging with ESO’s Very Large Telescope and the Hubble Space Telescope placed the source in a galaxy a few billion light‑years away, ruling out a Milky Way origin and implying far greater intrinsic power.
  • The observed repetition over roughly a day contradicts the standard view of gamma‑ray bursts as single, short‑lived catastrophic events.
  • The findings appear in peer‑reviewed reports, including an Astrophysical Journal Letters paper led by European researchers and a Nature Astronomy analysis from the Einstein Probe collaboration.
  • Proposed explanations under study include precursor or weaker jets, complex jet structure, shocks linked to a supernova, or a rare tidal‑disruption event involving an intermediate‑mass black hole.