A strange gamma-ray explosion that fired off repeated bursts from the same patch of sky over roughly seven hours has now been traced to its likely cause: a black hole ripping apart a star that strayed too close. The event, designated GRB 250702B, was first picked up in early July 2025 by multiple space telescopes and quickly drew attention for its extreme duration, which far exceeded the typical seconds-to-minutes lifespan of a gamma-ray burst. Two peer-reviewed studies and weeks of follow-up observations across the X-ray spectrum have now converged on an explanation that sits at the boundary between two of astrophysics’ most violent phenomena.
The unusual outburst is helping astronomers test how black holes feed and launch jets when they suddenly encounter new fuel. Instead of the clean, one-off flash of a collapsing massive star, GRB 250702B behaved more like a machine that sputtered, re-ignited, and slowly wound down. That pattern, researchers argue, is best explained if a supermassive black hole in a distant galaxy shredded an unlucky star and then spent hours gulping down the debris. The result was a sustained storm of high-energy radiation that first lit up the soft X-ray sky and then flared into the gamma-ray regime, leaving a lingering afterglow that observatories tracked for weeks.
How Einstein Probe Caught the First Signal
The initial detection came not from a gamma-ray instrument but from a soft X-ray telescope. China’s Einstein Probe flagged an X-ray transient designated EP250702a, which was active in the 0.5 to 4 keV energy band before and during the gamma-ray triggers that other satellites would soon register. That early X-ray activity turned out to be a critical clue. It meant the source was already producing high-energy radiation before the gamma-ray peaks arrived, a pattern inconsistent with the sharp, single-spike profile of most gamma-ray bursts. The Einstein Probe team at the National Astronomical Observatories of the Chinese Academy of Sciences reported precise sky coordinates with uncertainty estimates, giving other observatories a target to chase.
Within hours, NASA’s Fermi satellite recorded multiple gamma-ray triggers from the same region, labeled GRB 250702B, C, D, and E. The Swift satellite’s BAT instrument, using its GUANO data reconstruction pipeline and NITRATES analysis, confirmed the detections and produced localization skymaps with credible-region estimates for each trigger. The repeated firing from one location was itself unusual; most gamma-ray bursts are one-and-done events, the death cry of a massive star or the collision of two compact objects. This source kept going, producing distinct outbursts over a span that stretched toward a full day, and teams coordinated through NASA mission operations quickly organized deeper follow-up to capture the evolving signal.
Pinpointing the Source With Swift and Ruling Out Nearby Objects
Narrowing the position was the next priority. Swift’s X-Ray Telescope locked onto the source and sharpened the localization to arcsecond precision, reporting coordinates with a tight error radius. That level of accuracy is essential for matching a transient to a host galaxy or ruling out contamination from foreground stars. Equally telling was what Swift did not find: its Ultraviolet/Optical Telescope detected no coincident source at the position. The absence of an optical counterpart pointed away from a nearby stellar event and toward something far more distant and energetic, consistent with an extragalactic origin and a powerful central engine buried in a remote galaxy’s core.
The lack of a UVOT detection also constrained the type of explosion. A standard supernova-driven gamma-ray burst at modest distance would typically produce detectable optical and ultraviolet light within hours. The blank field suggested either extreme distance, heavy dust obscuration, or a progenitor mechanism that does not generate the same optical signature as a collapsing star. Researchers publishing in The Astrophysical Journal Letters characterized GRB 250702B as a day-long, repeating extragalactic transient and explored constraints on its distance and host environment, concluding that a tidal disruption scenario fit the data better than standard engine models. Their analysis showed that the energetics, spectral hardness, and temporal structure could be reconciled if a massive black hole suddenly began accreting stellar debris and powering a narrowly collimated jet aimed close to our line of sight.
NuSTAR and Chandra Track the Fading Glow
After the initial flurry of detections, two of NASA’s flagship X-ray observatories turned their mirrors on the source. NuSTAR conducted hard X-ray follow-up observations and found that the spectral shape fit an absorbed power-law model with a measured photon index, a form commonly associated with non-thermal emission from relativistic particles. The spectrum showed no iron emission lines and no reflection features, details that help distinguish between competing physical scenarios. An active galactic nucleus or certain accretion-disk geometries would typically imprint such features on the X-ray spectrum. Their absence pointed toward a cleaner, jet-dominated emission mechanism rather than a long-lived, steady accretion disk like those seen in ordinary quasars.
Weeks after the initial trigger, the Chandra X-ray Observatory picked up a late-time X-ray detection with a measured flux that was fainter but still clearly above background. That the source was still visible at such a late stage carried real diagnostic weight. The decay slope implied sustained emission rather than the steep fade expected from a simple afterglow produced by a one-off explosion plowing into surrounding gas. Taken together, the NuSTAR and Chandra data traced a long, slow decline that any proposed explanation for GRB 250702B would need to account for. The extended tail suggested that the central engine, likely a black hole accreting the remains of a disrupted star, continued to feed and emit X-rays well after the brightest gamma-ray flashes had faded from view.
Two Competing Explanations and One Leading Theory
The central question, what could produce repeated gamma-ray outbursts lasting nearly a day, drew two distinct but overlapping answers from the research community. A study in Monthly Notices of the Royal Astronomical Society proposed that GRB 250702B resulted from a black hole falling into a star, situating the event among the class of ultra-long gamma-ray bursts and modeling the expected counterparts and host-galaxy implications. In that picture, the compact object plunges into the stellar envelope, tapping into a large reservoir of material over an extended period and powering multiple high-energy episodes. The model can reproduce the long duration and repeating structure by allowing the infalling black hole to accrete in bursts as it spirals inward and disrupts different layers of the star.
A separate interpretation, reported by scientists analyzing the multi-mission data, argues that the better fit is a tidal disruption event in which a supermassive black hole shredded a star that wandered too close. In this scenario, the star is torn apart by intense tidal forces, and streams of stellar debris fall back toward the black hole, forming a transient accretion disk and launching relativistic jets. If one of those jets is pointed near Earth, the result is a gamma-ray and X-ray display that can persist and re-brighten as different clumps of material accrete. The authors of the Astrophysical Journal Letters study found that the timing and spectral evolution aligned naturally with this tidal disruption framework, especially when accounting for relativistic beaming and the viewing angle.
Why GRB 250702B Matters for Extreme Astrophysics
Beyond solving a single cosmic mystery, GRB 250702B is forcing astronomers to refine how they classify and interpret the universe’s most luminous explosions. Traditional categories separate short gamma-ray bursts, long bursts from collapsing massive stars, and tidal disruption events as distinct phenomena. GRB 250702B sits at the boundaries of these boxes, with a gamma-ray profile reminiscent of ultra-long bursts but a multiwavelength evolution that points strongly to a transiently feeding supermassive black hole. That ambiguity underscores the need for flexible models that can handle hybrid or intermediate events where multiple physical processes overlap.
The event is also a showcase for how coordinated high-energy astronomy can rapidly decode rare transients. From the first alert by Einstein Probe to the precise Swift localization, and from NuSTAR’s spectral measurements to Chandra’s late-time imaging, each instrument contributed a different piece of the puzzle. Teams drawing on expertise across NASA’s high-energy astrophysics programs combined those pieces into a coherent narrative of a star meeting its end in the grip of a black hole. As more sensitive surveys come online and automated alert networks improve, researchers expect to find additional GRB 250702B-like events, turning what is now one of the universe’s strangest explosions into a new laboratory for studying how black holes grow, launch jets, and shape their host galaxies.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
