Longest Gamma-Ray Burst Observed: Insights into Black Holes

Astronomers have detected the longest gamma-ray burst ever observed, designated GRB 250702B, which lasted seven hours. This significant event was first noticed on July 2, 2025, by NASA's Fermi Gamma-ray Space Telescope.

GRB 250702B stands out among approximately 15,000 gamma-ray bursts recorded to date, and it may be linked to an intermediate-mass black hole consuming a star. Typically, gamma-ray bursts last only a few minutes, making this discovery a unique opportunity for astronomers to study such cosmic explosions.

Team member Eliza Neights from George Washington University and NASA's Goddard Space Flight Center remarked that this outburst is unlike any seen in the past 50 years. Following Fermi's detection, astronomers utilized the Very Large Telescope in northern Chile to identify the galaxy from which the GRB originated, located billions of light-years away from the Milky Way.

Observations from the Victor M. Blanco 4-meter Telescope and the twin 8.1-meter International Gemini Observatory telescopes, led by Jonathan Carney from the University of North Carolina at Chapel Hill, provided further insights into the event.

Researchers indicated that the initial gamma-ray signal likely originated from a narrow jet of plasma moving at near-light speed, colliding with surrounding gas and dust. The host galaxy of GRB 250702B was found to be more massive than those associated with other gamma-ray bursts.

Current theories about the origins of gamma-ray bursts involve massive blue supergiant stars collapsing, the formation of neutron stars, or black holes ripping apart stars in tidal disruption events. However, GRB 250702B does not fit neatly into these established scenarios.

Theories being considered for this event include a black hole colliding with a helium-rich star, a smaller object experiencing a micro-tidal disruption event, or the involvement of an intermediate-mass black hole.

These intermediate-mass black holes, with masses ranging from 100 to 100,000 times that of the sun, are believed to be common but rarely detected. If GRB 250702B is indeed linked to an intermediate-mass black hole, it would mark the first observation of such a black hole producing a plasma jet after disrupting a star.

Carney noted that this research presents a fascinating challenge in cosmic archaeology, as scientists work to reconstruct details of events that occurred billions of light-years away, highlighting the ongoing quest to understand the universe's most extreme phenomena.