Gamma-ray bursts come in two classes. Short bursts (less than two seconds) arise from neutron star mergers — confirmed by the simultaneous detection of gravitational waves and electromagnetic radiation from GW170817. Long bursts (more than two seconds, typically tens of seconds) arise from the collapse of massive stars — the collapsar model, where a spinning stellar core produces a relativistic jet that punches through the dying star's envelope.
GRB 250702B lasted 25,000 seconds — nearly seven hours of prompt gamma-ray emission. It is the longest gamma-ray burst ever observed. The collapsar model cannot produce this. The stellar envelope through which the jet must propagate has a finite mass; the accretion timescale of a collapsing core is minutes, not hours. No known stellar progenitor has enough fuel to power a jet for this long.
Yuan, Jiang, and Dai (arXiv 2602.23299, February 2026) propose a different engine: a white dwarf orbiting an intermediate-mass black hole (IMBH) on a highly eccentric orbit. At each pericenter passage, the black hole's tidal field strips material from the white dwarf — a partial disruption. Each pass removes a fraction of the star, producing a burst of accretion onto the black hole and a corresponding episode of jet activity. The repeated partial disruptions, separated by the orbital period, produce a series of accretion events that collectively power the ultra-long prompt emission.
The final passage completely disrupts the white dwarf. The energetic debris from this last encounter produces relativistic ejecta at different velocities. When faster material catches slower material from earlier episodes, the internal collisions generate the luminous X-ray flare observed 1.3 days after detection. The external shock from the jet's interaction with the surrounding medium produces the extended X-ray and radio afterglow.
The model fits the multi-wavelength light curve: the prompt emission duration, the X-ray flare timing, the afterglow evolution. The engine isn't a collapsing star — it's an orbital machine that tears a white dwarf apart over many orbits.
If confirmed, GRB 250702B is evidence for an intermediate-mass black hole — the missing link between stellar-mass and supermassive black holes, whose existence has been inferred but rarely demonstrated. The burst found the black hole by dying next to it.