Astronomers have detected a series of gamma-ray bursts (GRBs) originating from a single cosmic source, designated GRB 250702B, that is unlike any observed in the last five decades. The phenomenon, first flagged by NASA's Fermi Space Telescope in July 2025, was subsequently confirmed by data from the Hubble Space Telescope and the European Southern Observatory's Very Large Telescope (VLT) in Chile's Atacama Desert.
Gamma-ray bursts are typically brief, lasting from milliseconds to minutes and releasing immense energy. However, GRB 250702B distinguished itself with an extraordinary duration of approximately 24 hours and a peculiar repetition of signals within a few hours. Antonio Martin-Carrillo, an astronomer at University College Dublin and a co-author of the study published in The Astrophysical Journal Letters, stated that this GRB is "unlike any other seen in 50 years of GRB observations." The Fermi telescope initially detected three bursts from this source over several hours on July 2, 2025, with further analysis of data from the Einstein Probe revealing activity nearly a day prior.
Initial observations suggested the source might be within our own Milky Way galaxy. However, the VLT's HAWK-I infrared camera provided crucial data that shifted this understanding, pinpointing the source outside the Milky Way, a finding later confirmed by the Hubble Space Telescope. While the exact distance is yet to be determined, the size and brightness of the host galaxy indicate it is located billions of light-years away, underscoring the immense power of the event.
Several hypotheses are being considered to explain this anomaly, including the highly atypical collapse of a very massive star or the destruction of an unusual star by an intermediate-sized black hole. These scenarios, however, do not fully account for all the observed properties of GRB 250702B unless the celestial objects involved are exceptionally rare. The Fermi Gamma-ray Space Telescope, launched in 2008, has been instrumental in studying these cosmic phenomena, having detected over 2,300 GRBs. This remarkable event highlights the vast diversity and complexity of cosmic phenomena and the ongoing need for dedicated research to unravel the processes behind such extreme energetic explosions.