Strange bursts of energy traveling at 99% of the speed of light are unlike anything scientists have seen before — Space Photo of the Week

Gamma-ray bursts (GRBs) are the most energetic type of explosion in the universe since the Big Bang, and are detected on average once every day. But what happened on July 2, 2025 was very unusual. NASA’s Fermi Gamma-ray Space Telescope, which has been in orbit around Earth since 2008, has recorded an unusually long-lived GRB that continues to emit in bursts for more than seven hours.

Astronomers sprang into action using telescopes around the world to detect the explosion’s afterglow and figure out where it came from.

The phenomenon, called GRB 250702B, was the longest-duration gamma-ray burst ever recorded. Astronomers now believe the explosion was the result of a previously unseen or rare type of explosion that shot a thin jet of material toward the solar system, traveling at at least 99 percent of the speed of light.

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Understanding GRB 250702B was not easy. The researchers traced its origins at every wavelength of light using all kinds of telescopes, including the twin 8.1-meter-diameter Gemini telescopes in Chile and Hawaii, the Very Large Telescope in Chile, the Keck Observatory in Hawaii, and the Hubble Space Telescope.

GRBs come from deep in space. The closest one originated more than 100 million light years away, according to NASA. GRB 250702B comes from a massive galaxy 8 billion light years away. This galaxy was so dusty that it blocked out all visible light.

The only light the telescope detected was in the infrared and high-energy X-ray wavelengths. Because of the thick dust within its host galaxy, the GRB is nearly invisible in normal visible light, the researchers reported in a study published Nov. 26 in The Astrophysical Journal Letters.

“This was the longest gamma-ray burst ever observed by humans, and its length is such that it defies any existing model for the cause of gamma-ray bursts,” said study lead author Jonathan Carney, a doctoral student in physics and astronomy at the University of North Carolina at Chapel Hill, in a statement.

Analysis shows that GRB 250702B could have been caused by the death of a massive star, the star being torn apart by a black hole, or the merger of a helium star and a black hole, with the black hole spiraling into the center of the massive star and causing it to explode from within.

“But we still don’t know which explanation is correct,” Carney said. “In the future, this phenomenon will serve as its own benchmark. When astronomers discover a similar explosion, they will ask whether it matches the properties of GRB 250702B or represents something completely different.”

For more sublime space images, check out this week’s space photo archive.