Scientists discover new type of cosmic catastrophe after record-long burst
NASA’s Fermi Gamma-ray Space Telescope recently detected an extraordinarily long gamma-ray burst, GRB 250702B, that blazed for about seven hours. Its strange pulses and off-center host location suggest a phenomenon never seen before.
Typical gamma ray bursts occur when a large star collapses into a black hole, creating a beam of light. Credit: A. Roquette/ESO
Gamma-ray bursts are among the most powerful events known, briefly releasing more energy than the Sun will emit in ten billion years. They usually last only a few seconds or minutes, powered when a massive star’s core collapses into a black hole and launches twin jets of plasma traveling nearly at light speed.
On July 2, 2025, the rules changed. Fermi’s detectors recorded a burst that kept emitting high-energy photons for about 25 000 seconds (7 hours). No previous burst had ever lasted that long.
At first, astronomers suspected a closer and less energetic source inside our own galaxy, since nearby events appear brighter and slower. But follow-up imaging from the European Southern Observatory’s Very Large Telescope (VLT) and the Hubble Space Telescope revealed a faint afterglow in a distant galaxy. Observations from NASA’s James Webb Space Telescope confirmed the distance: billions of light-years away.
That finding meant the explosion was not only extraordinarily long but also unimaginably energetic. Its light curve contained peculiar, repeating peaks roughly every second flickers so regular that they looked like the heartbeat of a dying star. Such rhythmic behavior had never been recorded in a GRB before.
Scientists race to explain the impossible
Within days, more than half a dozen research teams released preprints analyzing data across the electromagnetic spectrum, from gamma rays to radio waves. Each team proposed a different explanation, but none fit perfectly.
Daniel Perley of Liverpool John Moores University said the event “does not observationally look like any of the other things in that category that we’ve seen.” Brian Metzger of Columbia University called it “very unusual in its duration, a bit unusual in its environment, and then this weird periodicity makes it stick out.”
One suggestion involved a normal star orbiting a similar-mass black hole, losing material every time it passed close to the black hole. The accretion disk would be refueled on each orbit, producing multiple pulses of gamma rays. Metzger doubted that idea, pointing out that even a perfectly periodic engine would not necessarily produce such neat gamma-ray flashes, since the emission process itself is chaotic.
Another group turned to supermassive black holes at galactic centers. When a star strays too close to one, it can be torn apart in a tidal disruption event. Such events can produce powerful, long-lived jets. But GRB 250702B’s afterglow was not at its galaxy’s center it lay far out in the galactic suburbs. That ruled out a central supermassive black hole as the engine.
Some researchers considered a middle ground: a midsize black hole destroying a nearby star. Yet the burst’s brightness fluctuated every second, meaning the source had to be extremely compact far smaller than a midsize black hole could allow. None of the traditional explanations survived every test.
A radical idea takes shape: a black hole inside a star
As competing models failed, theorists began exploring a more extreme scenario. In this new picture, a stellar-mass black hole orbits inside a massive companion star that has lost its hydrogen layer and expanded into a helium-rich giant.
Friction inside the star’s outer envelope causes the black hole to spiral inward. Eventually, it plunges into the dense helium core at the center. Once embedded, it begins consuming the star from the inside out. The infalling material forms a disk around the black hole, launching jets that drill through the surrounding gas and radiate gamma rays into space.
Because this process unfolds gradually rather than explosively, the engine can keep running for many hours. The constant flow of material would power a long-lived jet, while irregularities in the infall rate could produce the observed one-second pulses.
Daniel Perley described this explanation as a “GRB-like phenomenon that allows for the longer time scale.” The model naturally explains the burst’s compactness, its long duration, and its off-center galactic position.
If correct, it reveals a new way massive stars and black holes interact one that could produce previously hidden classes of high-energy events.
What the fading afterglow reveals about the engine
Follow-up observations provided vital clues. The VLT measured an infrared afterglow fading over several days. Hubble confirmed its precise location in the galaxy’s outskirts. Radio telescopes later detected delayed flares, evidence of the jet colliding with surrounding gas.
The light’s spectrum matched synchrotron emission, produced when charged particles spiral through magnetic fields at near-light speed. The afterglow dimmed quickly, implying a narrow jet that happened to point almost directly toward Earth. That beam explains the burst’s extreme brightness despite its immense distance.
Sustaining a jet for seven hours demands an efficient way to extract energy from the black hole. One possibility is the Blandford–Znajek process, which taps rotational energy from a spinning black hole through magnetic fields. For it to work so long, the accretion flow must remain stable, and magnetic fields must stay strong—a challenge current simulations are only beginning to test.
If this mechanism operated inside a stellar envelope, it would merge ideas from supernova physics and compact-object mergers, showing that the line between them is thinner than scientists thought.
Waiting for the next monster burst
GRB 250702B has now faded from view, but its implications continue to ripple through astrophysics. Perley cautions that it is too soon to know which theory will stand: “You can’t say there’s any consensus. We will need to wait and see how things sort out as these papers are refereed.”
Future observations may decide. The James Webb Space Telescope and ground-based observatories are searching for any trace of a supernova that might have followed the burst. If none appears, that would strengthen the case for the black-hole-in-a-star scenario.
Next-generation missions such as the Einstein Probe and Theseus will watch the sky for more ultra-long GRBs. Finding additional examples would confirm whether GRB 250702B is a one-off or part of a broader, hidden population of slow cosmic catastrophes.
For now, this seven-hour explosion stands as one of the strangest ever seen. It shows that even after decades of studying the most violent events in the cosmos, nature still has ways to surprise us. Somewhere, far beyond our galaxy, a black hole may once have spiraled into a star’s heart and destroyed it from within.
References:
1 Long-lived gamma ray burst could signal a new kind of cosmic catastrophe – Science – October 8, 2025
I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.
Very interesting. Thanks for writing this article.