Astronomers have reported an unusual high-energy event that they say may be the first direct observational evidence of an intermediate-mass black hole disrupting and consuming a white dwarf star. The event, designated EP250702a and also known as GRB 250702B, was first detected on July 2, 2025 by the China-led Einstein Probe during a routine sky survey. The findings, published in Science Bulletin, stem from a multinational research effort coordinated by the Einstein Probe Science Center at the National Astronomical Observatories of the Chinese Academy of Sciences, with scientists including researchers from the University of Hong Kong.
The initial detection came from Einstein Probe's Wide-field X-ray Telescope, which identified a rapidly changing and exceptionally bright X-ray source. At nearly the same time, NASA's Fermi Gamma-ray Space Telescope recorded several gamma-ray bursts from the same area of the sky. Researchers later determined the event did not follow the pattern expected for a typical gamma-ray burst: Einstein Probe had already recorded steady X-ray emission from the location about a day before the gamma-ray activity began. Roughly 15 hours after the first detection, the source produced a series of intense X-ray flares and reached a peak luminosity of about 3 × 10^49 erg per second, placing it among the brightest instantaneous outbursts yet recorded.
Follow-up observations from major telescopes around the world located the event on the outskirts of a distant galaxy. Einstein Probe's Follow-up X-ray Telescope then tracked its evolution over about 20 days, during which the source dimmed by more than a factor of 100,000 and its emission shifted from harder to softer X-rays. Researchers said the combination of features including the early X-ray emission, extreme brightness, rapid evolution and off-center galactic location was difficult to reconcile with existing models of known high-energy events.
Based on that analysis, the team argues that the strongest explanation is a tidal disruption event in which an intermediate-mass black hole tore apart a white dwarf and began feeding on its remains. Lead author Dongyue Li said the early X-ray signal was key evidence that the event was not an ordinary gamma-ray burst. The researchers describe the interpretation as a leading candidate rather than a settled conclusion, saying confirmation would make the event a landmark observation in the study of intermediate-mass black holes and extreme cosmic transients.