NASA’s Fermi telescope detected a record-breaking gamma-ray burst lasting nearly seven hours. The unusual, multi-pulse explosion may have been caused by a rare intermediate-mass black hole tearing a star apart, challenging current models of cosmic explosions.
Fermi detected seven-hour gamma burst from star by black hole
Photo Credit: NOIRLab/NSF/AURA/M. Garlick
In July 2025, NASA's Fermi Gamma-ray Space Telescope detected a gamma-ray burst that lasted about seven hours, making it the longest on record. This event, dubbed GRB 250702B, far exceeds typical GRBs (which last milliseconds to minutes) and produced repeating pulses. Its odd behaviour has prompted theories, including that a “middleweight” black hole (hundreds to thousands of solar masses) tore apart a star.
According to the paper, on July 2, 2025, GRB 250702B was first observed by NASA's Fermi telescope. Over the course of the following few hours, it repeatedly triggered, releasing gamma rays for at least seven hours—nearly twice as long as any prior burst. It produced several emission spikes over the course of the following day before fading. For days, astronomers tracked its afterglow in optical light and X-rays. This extended, multi-peaked blast was a novel type of explosion because typical GRBs fade in a matter of minutes.
One hypothesis is that the jets of the gamma-ray burst were powered by an intermediate-mass black hole (about 100–100,000 times the Sun's mass) that tore apart a star. Such “middleweight” black holes are an eventuality, but they are hardly ever detected; therefore, if this were the case, it would be the very first time that one was seen producing a gamma-ray jet. A different idea is that a small black hole (only a few times the Sun's mass) was orbiting a compact “helium” star, eating it from the inside and causing the burst. Both scenarios have some evidence to support them, but neither is definite, and the actual cause of the event is still unknown.
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