The Seven Hour Explosion Nobody Could Explain
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On 2 July 2025, NASA's Fermi Gamma-ray Space Telescope detected a gamma-ray burst lasting over seven hours, nearly twice the duration of anything previously recorded. Not only was it the longest ever seen, it repeated, firing off multiple distinct bursts across an entire day. GRB 250702B, as it became known, doesn't fit any known category of astronomical explosion. But a new paper in Monthly Notices of the Royal Astronomical Society offers the explanation that a star torn apart by an intermediat
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The Seven Hour Explosion Nobody Could Explain By Mark Thompson - March 15, 2026 05:40 AM UTC | Extragalactic Gamma-ray bursts are the most violent explosions in the universe. In a fraction of a second, they can release more energy than the Sun will emit across its entire ten billion year lifetime. Most are over before you've had time to register them, gone in seconds, minutes at most. So when something arrived on 2 July 2025 that kept going for seven hours, fired three distinct bursts spread across an entire day, and then left behind an afterglow lasting months, astronomers knew immediately they were looking at something completely new. GRB 250702B, detected by NASA's Fermi Gamma-ray Space Telescope, is the longest gamma-ray burst ever recorded and it dwarfs all others in duration. Of the roughly 15,000 bursts catalogued since the phenomenon was first recognised in 1973, only a handful even approach its duration. Normal gamma-ray bursts don't repeat. They arise from cataclysmic, one time events, maybe a pair of neutron stars colliding, or a massive star collapsing in on itself. GRB 250702B did neither. "This is certainly an outburst unlike any other we've seen in the past 50 years," said one member of the detection team. The hunt for an explanation has occupied astronomers ever since. The orange dot at the centre of this image is GRB250702B, a gamma-ray burster that repeated several times over the course of a day, an event unlike anything ever witnessed before. (Credit : NASAA) The new paper published in Monthly Notices of the Royal Astronomical Society focuses on one of the most intriguing possibilities, an intermediate mass black hole. Black holes come in dramatically different sizes. At one end you have stellar mass black holes, a few times heavier than the Sun, formed when massive stars die. At the other, you have the supermassive monsters lurking at the centres of galaxies, millions or billions of solar masses across. In between sits a largely missing populatio...
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