Astronomers have observed a rare event where a black hole fell into a companion star and ate its way out, producing the longest-known gamma-ray burst. The burst, lasting about seven hours, was detected 9 billion light-years from Earth. This unusual scenario explains the extended duration of the phenomenon.
In July, NASA's Fermi Gamma-ray Space Telescope detected GRB 250702B, a gamma-ray burst originating approximately 9 billion light-years away. Unlike typical gamma-ray bursts, which are bright flashes from events like massive stars collapsing into black holes or neutron star mergers and last mere minutes, this one endured for 25,000 seconds—roughly seven hours—making it the longest on record.
Eliza Neights at NASA's Goddard Space Flight Center in the US, along with her colleagues, propose that a stellar-mass black hole spiraled into a companion star. The star's outer layers had expanded late in its life, causing the black hole to lose angular momentum and plunge toward the core. From there, the black hole consumed the star from the inside out, ejecting powerful jets that manifested as the observed burst.
"The only [model] which naturally explains the properties observed in GRB 250702B is the fall of a stellar-mass black hole into a star," the researchers state in their paper. This process may have also triggered a faint supernova, though it was too dim to detect at such a distance, even with the James Webb Space Telescope.
Hendrik van Eerten at the University of Bath in the UK describes the explanation as compelling: "The argument posed in this paper is a very compelling one." He notes the event as an "absurdity" but anticipates more detections with telescopes like the Vera Rubin Observatory in Chile. The findings are detailed in a preprint on arXiv (DOI: 10.48550/arXiv.2509.22792).