Mystery Explosion in Deep Space Lasted Hours, Defying Everything Scientists Expected

NASA’s James Webb Space Telescope reveals new clues about a mysterious cosmic explosion that defies expectations.

Researchers are investigating an unusual event in deep space that has left scientists searching for answers. The explosion lasted far longer than similar events ever recorded, making it one of the strangest high-energy phenomena observed in decades.

NASA recently reported that scientists used the James Webb Space Telescope to analyze GRB 250702B, a long gamma-ray burst. These bursts are among the most energetic phenomena known in the universe. In most cases, they occur when a massive star collapses and forms a black hole, releasing an intense but short burst of high-energy gamma radiation. GRB 250702B did not behave like a typical event of this kind.

A gamma ray burst that broke expectations

“This object shows extreme properties that are difficult to explain,” said Huei Sears, a postdoctoral researcher in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences who is studying the explosion. “Usually, these bursts are over in less than a minute, but GRB 250702B lasted for hours and even showed signs of X-ray activity a day prior.”

Astronomers from many institutions are now studying the data collected from the event. Among them are researchers working with China’s Einstein Probe as well as scientists using the National Science Foundation’s Very Large Array, which is widely recognized from its appearance in the science fiction film Contact.

The burst released waves of gamma radiation for at least seven hours. That duration is almost twice as long as the previous record holder for similar events. One possible scenario for how GRB 250702B might have formed is a black hole roughly three times the mass of the Sun, with an event horizon about 11 miles (18 kilometers) across, interacts with and merges with a nearby companion star.

“This is certainly an outburst unlike any other we have seen in the past 50 years,” said Eliza Neights, an astronomer at NASA’s Goddard Space Flight Center in Maryland.

Unusually long gamma-ray bursts require more exotic origins than typical GRBs. This animation illustrates one proposed explanation for GRB 250702B — the merger of a stellar-mass black hole with its stellar companion. As the black hole makes its last few orbits, it pulls large amounts of gas from the star. At some point in this process, the system begins to shine brightly in X-rays. Then, as the black hole enters the main body of the star, it rapidly consumes stellar matter, blasting gamma-ray jets (magenta) outward and causing the star to explode. Credit: NASA/LSU/Brian Monroe

Competing explanations for the explosion

Researchers are considering several possible explanations for the unusual burst. One possibility is that it represents an especially extreme gamma-ray burst. Another idea is that the event may instead be a tidal disruption event, which occurs when a star passes too close to a black hole and is torn apart by intense gravitational forces. In this scenario, the black hole involved could be thousands of times more massive than the Sun.

Scientists have also suggested a more unusual explanation in which a smaller black hole merged with a stripped-down stellar remnant known as a helium star. In this case, the black hole would effectively consume the star from within.

Regardless of the exact cause, the process produced powerful jets of energy that shot outward into space.

Global telescopes track the burst

The first detection of the explosion came from NASA’s Fermi Gamma-ray Space Telescope on July 2. Once the event was identified, observatories around the world began observing it. Because the burst was extremely bright, scientists were able to study it with multiple instruments working at different wavelengths.

Observations collected gamma rays, X-rays, infrared light, and radio waves. However, the event was not detected in visible light.

“Only through the combined power of instruments on multiple spacecraft could we understand this event,” said Eric Burns, an astrophysicist at Louisiana State University.

Webb reveals the distant host galaxy

Images obtained by the Hubble Space Telescope showed an unusual galaxy at the location of the explosion. At first, astronomers were unsure whether they were seeing two galaxies merging or a single galaxy divided by a thick band of dust across its center.

Further investigation with the James Webb Space Telescope helped clarify the situation. A spectral measurement taken by Webb revealed that the galaxy lies about 8 billion light-years away. This means the explosion took place billions of years before Earth formed.

To better understand the host galaxy, Sears led follow-up observations using Webb’s NIRCam instrument, the telescope’s primary near-infrared camera, several months after the burst occurred.

“In such vibrant and unprecedented detail, we see just one very large galaxy with a dust lane,” Sears said. “The galaxy has such a complex structure that it’s not 100% clear if there’s anything left to see of the explosion, but if there is, it’s really faint.”

A mystery that remains unresolved

These observations strengthen the possibility that GRB 250702B is indeed a gamma-ray burst rather than a tidal disruption event. Even so, scientists say the evidence is not yet conclusive.

“We have only seen a few tidal disruption events of this type, so we don’t know for sure how they’re supposed to evolve,” Sears said. “A lot of the studies on this explosion provide different, and sometimes contradictory, explanations. It’s still early in our understanding of what really happened.”

Whatever the final explanation turns out to be, researchers agree that the discovery is significant.

“This gives us a unique chance to study the extremes of how stars and black holes evolve,” Sears said. “GRB 250702B could even be the discovery of something unexpected and new.”

Reference: “Optical/Infrared Observations of the Extraordinary GRB 250702B: A Highly Obscured Afterglow in a Massive Galaxy Consistent with Multiple Possible Progenitors” by Jonathan Carney, Igor Andreoni, Brendan O’Connor, James Freeburn, Hannah Skobe, Lewi Westcott, Malte Busmann, Antonella Palmese, Xander J. Hall, Ramandeep Gill, Paz Beniamini, Eric R. Coughlin, Charles D. Kilpatrick, Akash Anumarlapudi, Nicholas M. Law, Hank Corbett, Tomas Ahumada, Ping Chen, Christopher Conselice, Guillermo Damke, Kaustav K. Das, Avishay Gal-Yam, Daniel Gruen, Steve Heathcote, Lei Hu, Viraj Karambelkar, Mansi Kasliwal, Kathleen Labrie, Dheeraj Pasham, Arno Riffeser, Michael Schmidt, Kritti Sharma, Silona Wilke and Weicheng Zang, 26 November 2025, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ae1d67

The Webb telescope also is supported by the European Space Agency (ESA), and the Canadian Space Agency (CSA).

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