Astrophysicist Helps Decode One of the Universe’s Strangest Explosions

NASA's James Webb Space Telescope uncovers clues about a mysterious cosmic blast that defies expectations

A Rutgers astrophysicist is helping to solve a cosmic puzzle that has astronomers scratching their heads. The mystery centers on a powerful explosion in space that lasted far longer than anything they have seen before.

Of the newly discovered gamma-ray burst, astrophysicist Huei Sears says, "It's still early in our understanding of what really happened."

NASA announced today that scientists using its James Webb Space Telescope studied GRB 250702B, a long gamma-ray burst, one of the brightest and most energetic events in the Universe. Normally, long gamma-ray bursts happen when a huge star collapses into a black hole, creating a quick, intense flash of high-energy gamma-ray light. This one didn't follow the rules.

"This object shows extreme properties that are difficult to explain," said Huei Sears, a postdoctoral researcher in the Department of Physics and Astronomyat 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."

She noted that observatories throughout the world are examining data collected from the object. This includes scientists from China's Einstein Probe, and the National Science Foundation's Very Large Array, known to the public from being featured in the science fiction movie, Contact.

The waves of gamma rays lasted at least seven hours, nearly twice as long as the previous record holder. NASA has released a video animationillustrating one possible explanation for the origin of GRB 250702B showing a black hole weighing about three times the Sun - with an event horizon just 11 miles (18 kilometers) across - orbiting and merging with a 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.

Scientists say the best explanation is that it is an extraordinary GRB or that it is an extraordinary tidal disruption event, where a middleweight black holethousands of times heavier than the Sun shredded a star that wandered too close. Another more exotic explanation is that a smaller black hole merged with a stripped-down star called a helium star, devouring it from the inside.

In any case, the black hole didn't just snack: It feasted, powering jets of energy that blasted across space.

This artist's concept depicts GRB 250702B (left of center) erupting within its host galaxy. This powerful explosion, first detected on July 2, blasted out narrow jets of particles at nearly the speed of light and exhibited repeated outbursts that lasted over 7 hours. Astronomers conducting rapid follow-up observations with multiple telescopes around the world found that the burst occurred within a large, extremely dusty galaxy.

NASA's Fermi Gamma-ray Space Telescope first detected the event on July 2, and other observatories quickly joined in. The burst was so powerful that no single instrument could capture all its details. Telescopes on Earth and in space worked together, collecting gamma rays, X-rays, infrared light and radio waves. It 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.

Images from the Hubble Space Telescope showed a strange galaxy at the burst's location. It wasn't clear if it was two galaxies merging or just one galaxy with a dark dust lane appearing to split the center into two. Later, a Webb spectrum of the galaxy revealed it to be about 8 billion light-years away. That means the explosion happened long before Earth even existed.

To help solve the mystery of the identity of the galaxy, Sears led observations from Webb's NIRCam, the telescope's primary near-infrared imager, of the galaxy months after the explosion.

"In such vibrant and unprecedented detail, we see just one very large galaxy with a dust lane," Sears said. "The galaxy has such 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."

That clue supports the idea that GRB 250702B was a gamma-ray burst, not a tidal disruption event. But the mystery isn't solved yet.

"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 it was, scientists agree it is rare and important.

"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."

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

This release includes excerpts from a NASA press releaseby Francis J. Reddy.

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