China's Tianguan satellite, also known as the Einstein Probe, has potentially witnessed a groundbreaking cosmic event: the intermediate-mass black hole devouring a white dwarf star. This discovery, as reported by the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), marks a significant milestone in astronomy, as it's the first time such an extreme occurrence has been observed. On July 2, 2025, during its routine sky survey, the satellite's Wide-field X-ray Telescope (WXT) detected an unusually bright and rapidly changing X-ray source, designated EP250702a. This event sparked a global collaboration among multiple telescopes across various wavelengths, all aimed at unraveling the mysteries of this extraordinary phenomenon.
The burst's characteristics, including its brightness evolution, radiation pattern, and spectral features, were notably distinct from any known cosmic explosion. In a recent issue of Science Bulletin, the NAOC research team proposed a compelling explanation: this event is likely a tidal disruption event, where an intermediate-mass black hole tears apart a white dwarf star. This phenomenon is akin to the rare jetted tidal disruption event, where a black hole rips a star apart, as explained by Zhang Wenda, an associate researcher at the NAOC.
A white dwarf, the ultra-dense remnant of a star's death, can have a 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 the solar mass, possess the tidal forces strong enough to shred a white dwarf 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 aligns with the rapid evolution and extreme luminosity observed in EP250702a.
Jin Chichuan, a researcher at the NAOC, emphasized the significance of the ultra-short timescale, extreme peak luminosity, and the subsequent soft X-ray 'afterglow' in supporting the scenario of a medium-mass black hole ripping apart a white dwarf. The Tianguan satellite's mission, as noted by Yuan Weimin, the principal investigator of the project, is to precisely capture the unpredictable and extreme transient phenomena in the universe. The discovery of EP250702a showcases the satellite's unique monitoring capability and China's significant contribution to global astronomical exploration.
