A team of international astronomers has identified a gamma-ray burst (GRB) unlike any seen before — repeating over a full day and originating beyond the Milky Way. Using the European Southern Observatory’s Very Large Telescope (VLT), scientists have pinpointed its location to a distant galaxy, but the cause of the explosion remains a cosmic mystery.
An extraordinary celestial phenomenon has left the world’s astronomers puzzled. Detected first by NASA’s Fermi Gamma-ray Space Telescope, a sequence of powerful gamma-ray bursts—named GRB 250702B—erupted not once but several times over the course of a day. The event defied every known model of such cosmic explosions, which typically last only seconds or minutes.
The discovery, reported by technology.org and based on research published in The Astrophysical Journal Letters, involved experts from the University of Utah, Radboud University in the Netherlands, and University College Dublin, among others.
“This immediately alerted us to the unusual nature of this explosion,” said Tanmoy Laskar, assistant professor of physics and astronomy at the University of Utah and co-author of the study.
The first alerts were triggered on July 2, 2025, when NASA’s Fermi telescope detected three bursts from the same source within hours. Additional data later revealed that the Einstein Probe—a joint mission of the Chinese Academy of Sciences, the European Space Agency (ESA), and the Max Planck Institute for Extraterrestrial Physics—had already recorded related activity almost a day earlier.
Such long-lasting, repeating GRBs are unheard of in modern astronomy. Initially, many experts believed the source was within our own Milky Way. However, observations from the European Southern Observatory’s Very Large Telescope (VLT) in Chile changed that view entirely.
“Before these observations, the general feeling in the community was that this GRB must have originated from within our galaxy. The VLT fundamentally changed that paradigm,” explained Andrew Levan of Radboud University, co-lead author of the study.
Using the VLT’s high-sensitivity HAWK-I infrared camera, astronomers located a faint galaxy suspected to host the event — later confirmed with the NASA/ESA Hubble Space Telescope.
“The fact that this object is extragalactic means that it is considerably more powerful,” said Antonio Martin-Carrillo, astronomer at University College Dublin and co-lead author.
The newly identified host galaxy is thought to lie billions of light-years away, though precise measurements are still pending.
Scientists are now debating two main scenarios. One possibility is the collapse of a massive star, producing a prolonged and irregular release of gamma radiation. Another hypothesis suggests the destruction of a star by a black hole, though that would require conditions never previously observed.
Whatever the cause, the discovery challenges existing theories of cosmic explosions and promises to reshape understanding of stellar death and black hole behavior.
To uncover more, astronomers are continuing to monitor the fading light with an array of instruments — including the VLT’s X-shooter spectrograph and the James Webb Space Telescope. Determining the host galaxy’s distance will be crucial to understanding the true scale and energy of this event.
“Traditional models can explain part of the data, but the distance and repetition make this one of the strangest GRBs we’ve ever seen,” said Laskar.
The study’s findings open new questions about how extreme cosmic events unfold — and whether yet-unknown astrophysical processes are at play in the depths of the universe.
Astronomers have detected an explosion of gamma rays that repeated several times over the course of a day,
