Einstein Probe Detects Potential Evidence of Intermediate-Mass Black Hole Consuming White Dwarf

A bright X-ray flare, designated EP250702a, was detected in July 2025 by the China-led Einstein Probe (EP) space telescope. Researchers are interpreting this extraordinary event, which occurred approximately 8 billion years ago, as potential evidence of a white dwarf star being tidally disrupted and consumed by an intermediate-mass black hole (IMBH).

The event exhibited characteristics distinguishing it from typical cosmic explosions: X-ray emission preceding a gamma-ray burst, extraordinary brightness, rapid evolution, and a location in the outskirts of its host galaxy.

Detection and Initial Observations

On July 2, 2025, the Einstein Probe's Wide-field X-ray Telescope (WXT) identified an exceptionally bright X-ray source during a routine sky survey. This source, also known as GRB 250702B, displayed rapid variations in brightness.

Approximately one day prior to the detection of gamma-ray bursts from the same celestial region by NASA's Fermi Gamma-ray Space Telescope, EP's WXT had already registered persistent X-ray emission. This sequence, with X-ray emission occurring before the gamma-ray burst, is considered atypical for high-energy cosmic explosions. Roughly 15 hours after the initial signal, the source produced a series of intense X-ray flares, reaching a peak luminosity of approximately 3 × 10⁴⁹ erg s⁻¹.

Unique Characteristics and Rapid Evolution

Prompt follow-up observations by various global telescopes, including EP's Follow-up X-ray Telescope (FXT), pinpointed the celestial object in the outskirts of a distant galaxy. The FXT tracked the source for about 20 days, during which its brightness diminished by over a hundred thousand times. Concurrently, its X-ray emission transitioned from higher-energy to lower-energy states.

Analysis of data from EP, combined with observations across the electromagnetic spectrum, revealed several distinguishing characteristics of EP250702a:

X-ray emission was detected before the associated gamma-ray burst.
The event demonstrated extraordinary brightness.
It evolved on a remarkably fast timescale.
Its location in the outskirts of its host galaxy differs from typical patterns observed in known high-energy cosmic events, which are often associated with younger, massive stars.

An Intermediate-Mass Black Hole Consuming a White Dwarf

Among theoretical scenarios, researchers propose that the observations are most consistent with an intermediate-mass black hole (IMBH) tearing apart and consuming a white dwarf star. This model suggests that the tidal forces of an IMBH, combined with the extreme density of a white dwarf, could produce the observed jet energies and evolutionary timescales. White dwarfs are extremely dense remnants of stars up to eight times the Sun's mass.

Astrophysicists from The University of Hong Kong (HKU), including Professor Lixin Dai and Dr. Jinhong Chen, contributed to the data interpretation and theoretical modeling. Dr. Chen's numerical simulations indicated consistency between the tidal disruption model and the observed data.

For a white dwarf to be visibly disrupted by a black hole in such an event, the black hole must fall within a specific mass range. Intermediate-mass black holes, with masses ranging from hundreds to tens of thousands of solar masses, are considered optimal for generating such visible disruptions. In contrast, stellar-mass black holes might produce shorter, less energetic flares, and most supermassive black holes would likely consume a white dwarf without significant visible disruption.

Profound Scientific Implications

If confirmed, this event would represent the first clear observational evidence of an intermediate-mass black hole tidally disrupting a white dwarf and producing a relativistic jet.

Such a discovery could contribute significantly to:

A better understanding of the population of intermediate-mass black holes, which have been challenging to identify.
Opening new avenues for studying the growth mechanisms of black holes.
Providing insights into the ultimate fate of compact stars.
Advancing the field of multi-messenger astronomy.

Global Collaboration Drives Discovery

The research characterizing this event was coordinated by Dongyue Li and Wenda Zhang of the Chinese Academy of Sciences' Einstein Probe Science Center and published as a cover article in Science Bulletin. The collaborative team included over 40 universities and research institutions internationally. The Einstein Probe satellite project itself is led by the Chinese Academy of Sciences in collaboration with partners such as the European Space Agency (ESA), the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, and the French National Centre for Space Studies (CNES).