quick facts
What is it: Gamma-ray burst GRB 250702B
Where is it: 8 billion light years away, in the constellation Scutum.
When it was shared: December 8, 2025
A gamma-ray burst (GRB), the most energetic type of explosion in the Universe since the Big Bang, is detected on average once a day. But what happened on July 2, 2025 was very unusual: NASAThe Fermi Gamma-Ray Space Telescope, which has orbited Earth since 2008, detected an unusually long-lived gamma-ray burst that continued to emit bursts for more than seven hours.
The event, called GRB 250702B, was the longest-lasting gamma-ray burst ever recorded. Astronomers now believe it was due to a previously unobserved or rare type of explosion that released a narrow stream of material towards Earth. solar systemtraveling at least 99% speed of light.
Understanding GRB 250702B was not easy. Researchers have used all kinds of telescopes to trace its origins in all wavelengths of light, including the two 8.1-meter Gemini telescopes in Chile and Hawaii, the Very Large Telescope in Chile, the Keck Observatory in Hawaii and Hubble Space Telescope.
GRBs come from the depths of the Universe; even the closest one originated more than 100 million light years away. according to NASA. GRB 250702B originated from a massive galaxy 8 billion light-years away that, crucially, is so dusty that it blocks all visible light.
The only light detected by the telescopes was infrared and high-energy X-rays. Because of the thick dust in the host galaxy, the gamma-ray burst was almost invisible in normal visible light, the researchers reported in a study published Nov. 26 in the journal Letters from an Astrophysical Journal.
“It was the longest gamma-ray burst that humans have ever observed—long enough that it doesn't fit into any of our existing models of what causes gamma-ray bursts.” Jonathan Carneysaid the study's lead author and doctoral student in physics and astronomy at the University of North Carolina at Chapel Hill. statement.
Analysis suggests that GRB 250702B could be caused by the death of a massive star, the tearing of a star by a black hole, or the merger of a helium star and a black hole, where the black hole spirals into the core of a massive star, causing an explosion from the inside.
“But we can’t yet say which explanation is correct,” Carney said. “In the future, this event will provide a unique reference point—when astronomers discover similar explosions, they will ask whether they match the properties of GRB 250702B or are something completely different.”
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