Black Hole Tears Apart a Star — And Triggers the Longest Gamma-Ray Burst Ever Recorded

Astronomers are piecing together one of the most puzzling cosmic events of the year: a black hole appears to have destroyed a star and produced an unprecedented seven-hour gamma-ray blast. The event, labeled GRB 250702B, was first flagged on July 2 by NASA’s Fermi Gamma-ray Space Telescope and has prompted intense, worldwide follow-up across many observatories.

What Observatories Saw

The discovery sequence was unusual. The Einstein Probe (a Chinese–European mission) recorded an X-ray brightening at the same sky location about a day before Fermi detected the gamma rays. Typically high-energy emission peaks early and fades; here the order was reversed, a pattern not seen since gamma rays were discovered in 1973.

Swift narrowed the position, and the Very Large Telescope (VLT) in Chile detected a fading afterglow near a faint smudge. Hubble imaging identified that smudge as a previously unknown galaxy, and the James Webb Space Telescope used infrared observations to show the light left that galaxy roughly eight billion years ago. Dense dust in the host galaxy — and the line of sight through the Milky Way — likely obscured parts of the explosion.

Why This Is So Strange

All teams agree that the star’s destruction produced a relativistic jet — material accelerated to nearly the speed of light that generated the observed gamma rays. The core mystery is: what powered that jet?

“It was a very unusual, exotic explosion that we probably had never seen before,” said Eleonora Troja, astrophysicist at the University of Rome Tor Vergata.

Leading Explanations

Researchers have proposed three main scenarios, each with different implications for the black hole’s mass and the star’s fate:

• Stellar-Mass Black Hole Merges With A Helium Star: A compact black hole (roughly 5–30 solar masses) could merge with a stripped helium star, eat it from the inside out, power a jet and leave just a larger black hole behind. This idea is supported by similarities to known stellar-mass black hole signals and is argued for in recent peer-reviewed work.
• Micro-Tidal Disruption Event: A stellar-mass black hole could tidally disrupt a companion star (a scaled-down version of events normally associated with supermassive black holes). This fits the idea of a small black hole producing rapid variability.
• Intermediate-Mass Black Hole (IMBH) Tearing Apart A White Dwarf: An IMBH (100–100,000 solar masses) ripping apart a white dwarf could also explain the burst, but IMBHs are rare and the rapid one-second variability observed by Fermi is harder to reconcile with a larger object.

Eric Burns and colleagues note that the gamma-ray brightness varied on roughly one-second timescales. Because larger objects change more slowly (information and light take longer to cross them), that rapid variability favors a relatively small, stellar-mass black hole. Still, some researchers caution that alternative explanations cannot yet be ruled out.

Ongoing Work

The event has produced at least ten papers on the preprint server arXiv and several peer-reviewed studies. Teams continue monitoring the site in X-rays and radio wavelengths to search for late-time signatures — for example, a concealed supernova — that could distinguish between models.

As Brendan O’Connor of Carnegie Mellon University and many others emphasize, fast global coordination was crucial: teams worked around the clock (and through holiday periods) to point telescopes and collect multiwavelength data. The outcome will help fill gaps in our understanding of how compact objects interact with stars.

Why This Matters

This event opens a new window onto extreme astrophysical collisions. Whether it reveals a novel type of stellar-mass black hole interaction, a rare micro-tidal disruption, or the long-sought signatures of an intermediate-mass black hole, GRB 250702B is forcing astronomers to refine models and follow up aggressively across the electromagnetic spectrum.

Researchers describe the event as a reminder of how much the universe can surprise us when observed with new instruments and coordinated global effort.