China's Tianguan satellite likely captures black hole devouring white dwarf: study

BEIJING -- China's Tianguan satellite -- also named the Einstein Probe -- has likely captured an intermediate-mass black hole tearing apart and devouring a white dwarf star, marking the first time such an extreme event has been observed, according to the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).

During its routine sky survey, the satellite's Wide-field X-ray Telescope (WXT) detected an extraordinarily bright and rapidly changing X-ray source on July 2, 2025. Designated EP250702a, this event triggered a global multi-telescope campaign across various wavelengths.

The burst's characteristics, including its brightness evolution, radiation pattern, and spectral features, were markedly different from those of any known cosmic explosion.

In a cover article published in the latest issue of Science Bulletin, the research team from the NAOC proposed a compelling explanation: this is likely the tidal disruption event of a white dwarf by an intermediate-mass black hole.

"This phenomenon closely resembles the rare occurrence of a jetted tidal disruption event, where a black hole tears apart a star," explained Zhang Wenda, an associate researcher at the NAOC.

A white dwarf is the ultra-dense remnant left after a star's death, with an average density up to a million times that of the Sun. Theoretical studies suggest that only intermediate-mass black holes, weighing from hundreds to hundreds of thousands of times that of the solar mass, possess tidal forces strong enough to shred such a compact object rather than swallow it whole.

This process is predicted to produce a brief, intense, and violent burst of energy, likely accompanied by a bright, fast-moving jet, which is consistent with the rapid evolution and extreme luminosity observed in EP250702a.

"The ultra-short timescale, extreme peak luminosity, and the subsequent emergence of a soft X-ray 'afterglow' strongly supported the scenario of a medium-mass black hole ripping apart a white dwarf," said Jin Chichuan, a researcher at the NAOC.

Stars approaching black holes close enough can be torn apart by strong tidal forces, producing electromagnetic flares. To date, more than 100 tidal disruption events have been observed, most involving normal gaseous stars whose debris falls onto black holes, sustaining flares for years, the article noted.

"The mission of the Tianguan satellite is to precisely capture the unpredictable and extreme transient phenomena in the universe," said Yuan Weimin, principal investigator of the satellite project and a researcher at the NAOC.

"The discovery of EP250702a fully demonstrates the unique monitoring capability of WXT," said Yuan. "It not only proves our ability to be the first to capture the universe's most extreme moments but also highlights China's contribution to global astronomical exploration."