The event recorded on July 2, 2025 and named “EP250702a” stunned the scientific community and for good reason: such a phenomenon had never been captured by researchers. That day, the WXT instrument of the Einstein Probe (EP) mission captured a burst of X-rays of prodigious intensity. It was then the start of an international hunt involving the best telescopes in the world, from NASA’s Fermi space telescope to the observatories of the University of Hong Kong.
What immediately intrigued researchers was the order in which these rays reached us. Usually, cosmic explosions like gamma-ray bursts precede or accompany X-ray emissions. Here, the signal started to shine well before literally exploding in brightness. About fifteen hours after the first alert, the phenomenon reached its peak, becoming one of the brightest ever observed in this energy range.
Then everything happened very quickly. In just twenty days, the source saw its brightness collapse by a factor of 100,000. For Doctor Dongyue Li, of the National Astronomical Observatory of China, the observation is clear: “This early X-ray signal is crucial. It tells us that it was not an ordinary gamma-ray burst.»
The analysis of the data collected prompted scientists to explore a daring theory: the location of the explosion, on the outskirts of its galaxy and not at its center, as well as the speed of its evolution, point to a not-so-usual suspect: a black hole of intermediate mass.
The “missing link” finally unmasked?
More massive than stellar black holes but much smaller than the supermassive monsters that sit at the heart of galaxies, these cosmic monsters are the “missing links” in the evolution of our universe. In the case of EP250702a, this predator would have crossed paths with a white dwarf, the dense corpse of an ancient star. Under the influence of gravitational tidal forces, the white dwarf was literally torn apart, releasing colossal energy before being swallowed up.
According to The Debrief, this observation is a major breakthrough. Dr Jinhong Chen, from the Department of Physics at the University of Hong Kong and co-lead author of the study, points out that “combining the tidal forces of an intermediate-mass black hole with the extreme density of a white dwarf can produce jet energies and time scales highly consistent with observational data».
If this interpretation is confirmed, it would finally validate the existence of these intermediate black holes, until now only assumed. This discovery paves the way for future studies on the growth of these space ogres.
Astronomers now have high expectations from the future LISA interferometer or new generation giant telescopes to track the gravitational waves resulting from these stellar disruptions.
