Chinese Researchers Challenge Gamma-Ray Burst Origin Theory | GRB 250702B

BEIJING – Chinese researchers have proposed a new model to explain the origin of an unprecedentedly long gamma-ray burst (GRB), GRB 250702B, challenging existing astrophysical understanding of these powerful cosmic explosions. The burst, initially detected on July 2, 2025, by NASA’s Fermi Gamma-ray Space Telescope, lasted for a record-breaking seven hours, significantly exceeding the duration of typical GRBs.

A team from the Chinese Academy of Sciences Institute of High Energy Physics analyzed data from the Insight-HXMT and GECAM satellites, conducting a comprehensive search of emissions spanning 30 days around the event. Their analysis revealed the gamma-ray emission persisted for approximately 29 hours, dwarfing previous records. The team also identified unique variations in the accompanying X-ray radiation, according to a research article recently published in The Astrophysical Journal Letters.

The researchers hypothesize that GRB 250702B originated from a supergiant star with a mass considerably greater than our Sun. Unlike the progenitors of conventional GRBs, the collapse of such a massive star can unfold over an extended period, lasting for days. According to the model, the star’s core initially collapsed into a black hole, which then rapidly accreted the surrounding stellar material, generating relativistic jets traveling at near-light speed – the source of the observed gamma-ray burst.

Subsequent to this initial accretion phase, slower-moving jets were generated, emitting X-ray radiation. This explains the unusual observation of X-ray emissions preceding the arrival of gamma rays by a full day, a phenomenon not predicted by standard GRB models, as noted by researchers at CERN. The burst emerged from near the edge of its host galaxy’s disc, approximately 1900 light-years from the galactic center, according to images from the Hubble Space Telescope and the James Webb Space Telescope.

GRBs are the most energetic explosions in the universe, typically resulting from the death of massive stars or the merging of compact objects like black holes and neutron stars. Shorter GRBs, lasting less than two seconds, are generally attributed to the merger of these compact objects. “Ultralong” GRBs, like GRB 250702B, have been previously hypothesized to originate in the collapse of massive blue supergiants, allowing for prolonged accretion onto a central black hole. Still, the extended duration and preceding X-ray emissions of GRB 250702B set it apart from all previously observed events.

Astronomers had previously observed an unusual, long-lasting, and repeating gamma-ray burst, GRB 250702B, in September 2025, as detected by the European Southern Observatory’s Very Large Telescope. That event was described as lasting 100-1000 times longer than most GRBs, and unlike any observed in the preceding 50 years of GRB observation.