What is GRB 250702B and why is it record-breaking?

GRB 250702B is a gamma-ray burst discovered July 2, 2025, lasting 7 hours (25,000+ seconds)—the longest ever observed in 50+ years of GRB astronomy. It nearly doubled the previous record of 4 hours, exhibiting multiple distinct gamma-ray episodes and unprecedented precursor X-ray activity extending back a full day before the initial gamma-ray detection.

What is a tidal disruption event and how does it produce gamma rays?

A tidal disruption event occurs when a star ventures so close to a black hole that the black hole's differential gravitational force (tidal force) exceeds the star's self-gravity. The star is stretched ("spaghettified") and torn apart. Material streams around the black hole, forming an accretion disk that heats to millions of Kelvin and launches relativistic jets that produce gamma-ray emission.

Why couldn't standard gamma-ray burst models explain the 7-hour duration?

Typical GRB mechanisms (stellar collapse or neutron star merger) produce impulsive energy releases lasting seconds to minutes. The black hole "power source" shuts off quickly. A tidal disruption event, however, provides a continuous supply of stellar material feeding the accretion disk for hours, sustaining jet production and gamma-ray emission far longer than standard mechanisms permit.

Could GRB 250702B help discover intermediate-mass black holes?

Yes—tidal disruption events from intermediate-mass black holes (IMBHs, masses 100-100,000 solar masses) could produce extended-duration GRBs like GRB 250702B. Future discoveries of similar ultra-long GRBs would enable statistical characterization of the IMBH population, providing a new census of these elusive black holes and revealing their prevalence in galaxies.

Longest Gamma-Ray Burst GRB 250702B Black Hole Discovery

On July 2, 2025, at 10:39 UTC, the Gamma-ray Burst Monitor aboard NASA's Fermi Gamma-ray Space Telescope detected an extraordinary cosmic explosion. What began as a typical high-energy alert would become the most extraordinary gamma-ray burst ever observed in the more than 50 years since gamma-ray bursts were first discovered. Named GRB 250702B, the burst defied all conventional expectations by lasting not minutes but hours—a staggering seven hours of continuous and episodic gamma-ray emission. The previous record holder, GRB 111209A, had lasted roughly four hours. GRB 250702B exceeded it by three additional hours, pushing the boundaries of how long a gravitational phenomenon could maintain such violent, energetic output. Yet the burst's remarkable duration was merely its most obvious distinguishing feature. Even more peculiar was that X-ray observations from China's Einstein Probe had detected energetic radiation a full day before any gamma rays arrived—a slow buildup to the catastrophic main event. The brightest episodes occurred with multiple distinct flare peaks separated by minutes to hours, a pattern suggesting repeated energy release rather than a single continuous explosion. The location was equally surprising: the burst emerged not from the nucleus of its host galaxy, where the most massive black holes reside, but from the galactic periphery, nearly 1,900 light-years from the galactic center. As a multinational team of astronomers pored over data from NASA's fleet of space telescopes, the European Hubble and James Webb observatories, and ground-based facilities worldwide, a revolutionary picture emerged. GRB 250702B resulted not from a stellar collapse or neutron star merger—the two mechanisms previously thought capable of producing gamma-ray bursts—but from something far more exotic and violent: a black hole tearing a star apart in a catastrophic tidal disruption event. The discovery fundamentally challenges our understanding of black hole physics, jet formation, and the mechanisms by which some of the universe's most energetic phenomena are unleashed.

Gamma-Ray Bursts: The Universe's Most Violent Explosions

Gamma-ray bursts are the most powerful, most luminous electromagnetic explosions known to exist in the universe. A single gamma-ray burst can, in seconds, release as much energy as our Sun will emit across its entire 10-billion-year lifetime. These explosions are so bright and energetic that they remain detectable from across the observable universe, from distances of billions of light-years. For decades after their discovery in 1973 through serendipitous detection by military satellites, the origin of gamma-ray bursts remained one of astronomy's greatest mysteries. Were they nearby, relatively faint events in our galaxy, or distant, extraordinarily luminous events in other galaxies? The answer came only in 1997 when the Italian-Dutch satellite BeppoSAX, for the first time, enabled rapid location and follow-up observation of a GRB's afterglow by ground-based telescopes. The discovery revealed that most gamma-ray bursts originated in distant galaxies—extragalactic events so luminous that they momentarily outshone entire galaxies containing billions of stars. The physical origin of gamma-ray bursts gradually became clear through decades of observations and theoretical work. Most GRBs fall into two categories: "long" GRBs, lasting seconds to minutes, originating from the collapse of massive stars into black holes; and "short" GRBs, lasting milliseconds to seconds, originating from mergers of neutron stars or neutron-star-black-hole systems. Both mechanisms involve the formation of a new black hole and the launch of relativistic jets—beams of particles accelerated to nearly the speed of light. These jets produce gamma rays through various mechanisms as they propagate outward at tremendous speeds. The classification seemed comprehensive, encompassing essentially all observed gamma-ray bursts. Until GRB 250702B shattered this paradigm.

GRB 250702B: An Outlier That Rewrites the Rules

Discovery and Initial Observations: Breaking the Duration Record

The Gamma-ray Burst Monitor on Fermi detected the initial burst and triggered multiple times over a three-hour period, a behavior already unusual for a single GRB event. Simultaneously, NASA's Neil Gehrels Swift Observatory, the Russian Konus instrument aboard NASA's Wind spacecraft, Japan's Monitor of All-sky X-ray Image instrument on the International Space Station, and the IKAROS spacecraft detected the same event, confirming its authenticity and providing a coordinated, multi-satellite observational picture. As the initial gamma-ray activity progressed, the brightest episode continued far longer than standard GRB models would predict. Typically, the main gamma-ray emission from a GRB lasts seconds to perhaps a minute. Very rarely, a GRB might continue for several minutes. The previous record holder, GRB 111209A, had amazed astronomers by continuing for roughly 14,600 seconds—approximately 4 hours. GRB 250702B exceeded this record by more than 10,000 seconds, with the gamma-ray activity sustaining for at least 25,000 seconds—7 hours and change. "This is certainly an outburst unlike any other we've seen in the past 50 years," noted Eliza Neights, lead scientist on the analysis at NASA's Goddard Space Flight Center. The duration alone was revolutionary, but the structure of the burst made it even more peculiar. Rather than a single continuous emission brightening and fading, the gamma-ray light showed multiple distinct episodes—separate bursts separated by quiet periods, each lasting seconds to minutes. This episodic structure, never before observed on such a timescale in a gamma-ray burst, suggested a fundamentally different physical mechanism than those thought to power standard GRBs.
The Precursor: X-Rays Before Gamma Rays

One of the most remarkable discoveries came from analysis of data from China's Einstein Probe, an X-ray observatory monitoring the sky for transient events. Researchers discovered that soft X-rays—radiation in the 0.5-4 kiloelectronvolt energy range—had been detected from GRB 250702B for a full day before the first gamma-ray detection. This discovery reframed our understanding of the event's initiation. Rather than a sudden, catastrophic explosion, GRB 250702B appeared to involve a gradual buildup of energy over at least a day, culminating in the violent gamma-ray outburst. This precursor X-ray activity suggests that the mechanism driving the burst involved a gradual process of energy accumulation, quite unlike the impulsive dynamics typically associated with stellar collapse or neutron star mergers. The detection of precursor X-rays provides crucial clues to the event's origin. They indicate that the system was gradually heating and energizing before unleashing its most violent activity. In standard merger scenarios (neutron star-neutron star or black hole-neutron star), the merger itself is sudden, occurring in seconds. In stellar collapse scenarios, the buildup to core collapse involves seconds to minutes of dynamical readjustment, not days. The presence of day-long precursor activity hints at a different physical process altogether—one involving gradual tidal forces and mass transfer over extended timescales.
Location and Host Galaxy: Ruling Out Supermassive Black Holes

High-resolution imaging from the Hubble Space Telescope and James Webb Space Telescope pinpointed the precise location of GRB 250702B's host galaxy in the constellation Scutum, near the crowded, dusty plane of our Milky Way. More crucially, these images revealed something striking: the gamma-ray burst's location was not at the galaxy's nucleus but displaced nearly 1,900 light-years from the galactic center—a significant distance placing the source in the galactic periphery or disk. This location is critical because the most massive, supermassive black holes (millions to billions of solar masses) reside exclusively at the centers of galaxies. The offset location thus ruled out the supermassive black hole hypothesis, despite the burst's exceptional duration suggesting otherwise. The host galaxy itself was surprisingly large—containing more than twice the mass of the Milky Way—and showed no signs of active supermassive black hole activity (no active galactic nuclei signature). If GRB 250702B truly originated from a black hole tearing apart a star, that black hole must be either a stellar-mass object (produced by the death of a massive star) or an intermediate-mass black hole (IMBH)—objects of unclear origin and still incompletely understood. The location was thus not a minor detail but a crucial constraint that forced the scientific community to consider exotic scenarios previously relegated to theoretical speculation.

Analysis I: Tidal Disruption Events and Spaghettification

What Is a Tidal Disruption Event? Gravity's Stretching Force

A tidal disruption event (TDE) occurs when a star approaches a black hole so closely that the black hole's tidal force—the differential gravitational force across the star's diameter—exceeds the star's own self-gravity. Tidal forces arise from the fact that gravity decreases with distance. The side of a star closest to a black hole experiences stronger gravitational acceleration than the side farther away. For a star approaching a supermassive black hole, these tidal forces can be relatively gentle, and a star might survive the encounter with merely parts of its atmosphere stripped away. But for a star approaching a stellar-mass or intermediate-mass black hole, the tidal forces become apocalyptic. The differential gravitational force stretches the star like taffy, elongating it into a thin stream—a process colloquially termed "spaghettification." The star's self-gravity, which holds it together as a sphere, is overwhelmed by the black hole's tidal force. The star breaks apart, its material streaming away in a narrow filament following the black hole's gravitational field. This tidal stream of material loops around the black hole, with some material captured into a bound orbit forming an accretion disk around the black hole. Other material, moving with trajectories taking it too close to the black hole, plunges inward and is consumed. The accretion disk heats to extreme temperatures through friction as material spirals inward, eventually reaching temperatures of millions of Kelvin. At these temperatures, the disk becomes an intense source of X-rays, ultraviolet light, and optical radiation. If the accretion conditions are favorable, relativistic jets—beams of particles and radiation traveling at nearly the speed of light—can be launched from near the black hole's event horizon.
The Precursor Emission: Tidal Forces Before Disruption

The detection of X-ray emission a day before the gamma-ray burst may reveal the precursor phase of the tidal disruption. As the star initially approaches the black hole, tidal forces begin to distort its shape, stretching it tidally. Before complete disruption, the star may still possess its coherence, but tidal forces are tidally stretching its outer layers, heating them, and stripping away material. During this phase, the star is not yet in free-fall toward the black hole but is in a close, decaying orbit. With each orbit, gravitational radiation—ripples in spacetime itself—carries away energy and angular momentum, causing the orbit to decay. The combination of orbital decay and tidal stretching could produce the precursor X-ray emission detected by the Einstein Probe. As the star's orbit decays closer and closer to the black hole, the tidal forces intensify, the heating increases, and the material loss accelerates. Eventually, the tidal forces overcome the star's self-gravity completely, and the star undergoes the violent spaghettification and disruption that releases the catastrophic energy observed as gamma rays.
Accretion Disk Instability and Jet Formation

Once the star is disrupted and its material forms an accretion disk around the black hole, the disk becomes extremely hot and unstable. The accretion disk is supplied with material from the tidal stream—a continuous supply of stellar material as the stream orbits and is tidally disrupted. Initially, the accretion rate is extraordinarily high—the black hole is consuming material at rates exceeding its Eddington limit, the rate at which radiation pressure prevents further infall. Under these extreme conditions, the accretion disk becomes prone to instabilities. Magnetic reconnection, the sudden reconfiguration of magnetic field lines, can occur in the disk, releasing magnetic energy catastrophically. These reconnection events heat the disk and accelerate particles to relativistic speeds. The intense magnetic fields in the disk can channeling material into relativistic jets. These jets, once launched, propagate outward at speeds approaching the speed of light, producing gamma-ray emission as they go through a variety of mechanisms: inverse Compton scattering (high-energy electrons colliding with photons), synchrotron emission (electrons spiraling in magnetic fields), and potentially other processes. The episodic gamma-ray bursts observed during GRB 250702B's 7-hour duration could result from repeated episodes of magnetic reconnection, jet formation, and gamma-ray emission, each lasting seconds to minutes, separated by brief pauses as the disk configuration evolves.

Analysis II: Why Standard Models Fail and New Physics Emerges

The Duration Problem: Why 7 Hours Should Be Impossible

Standard gamma-ray burst models cannot easily produce a burst lasting 7 hours. In a stellar collapse scenario, a massive star's core collapses catastrophically to form a black hole. The collapse itself is impulsive, lasting seconds. The collapse triggers the formation of relativistic jets, which propagate outward through the star's envelope and eventually break free into space. The jet's initial energy comes from the rotational energy of the progenitor star and gravitational binding energy released during core collapse. However, once the core has collapsed and the jets have broken free, the power source is exhausted. The accretion timescale for material to be consumed and form jets is very short—seconds to minutes at most. After this brief period, the jet production shuts off, and the gamma-ray burst ends. Extending a gamma-ray burst to 7 hours under these conditions would require the black hole to somehow continue powering jets for hours—an impossibility in standard models. In a neutron star merger scenario, the collision itself is impulsive, lasting seconds to minutes. The merger produces a hypermassive neutron star (a state of matter supported by rapid rotation against its own weight) or a black hole, depending on the total mass. The formation of this object and the launch of jets occur on dynamical timescales, seconds to minutes. Once the merger is complete and material has been ejected, the power source for jet production ceases. Again, extending jet production to hours is difficult or impossible. Yet GRB 250702B's black hole "refused to shut off," as lead researcher Brendan O'Connor put it. The black hole continued accreting material and powering jets for hours, far longer than standard models predict.
The Tidal Disruption Solution: A Continuous Supply of Fuel

The tidal disruption scenario offers a natural explanation for GRB 250702B's exceptional duration. In a tidal disruption event, the "power source" is not a sudden, impulsive collapse or merger but rather a star—a massive reservoir of material with a binding energy on order of 10⁵¹ ergs (depending on the star's mass and structure). As the star is tidally disrupted, its material is not consumed all at once but rather in a stream that loops around the black hole. The material falls inward on dynamical timescales measured in orbital periods. For a stellar-mass black hole, an orbital period of a few stellar radii distance might be on order of seconds to minutes. However, the tidal stream itself possesses an orbital timescale determined by the black hole's mass and the stream's separation from the black hole. For a relatively large tidal stream, this timescale can be extended to tens of minutes or hours. The continuous feeding by the tidal stream could thus sustain accretion and jet production for extended periods—hours or longer. The episodic gamma-ray bursts observed could represent multiple passages of the tidal stream across the inner accretion disk, each producing a burst of jet activity and gamma-ray emission. As time progresses and more of the stellar material is consumed, the accretion rate diminishes, and eventually, the gamma-ray emission ceases. The total duration depends on the star's mass, the black hole's mass, and the initial conditions of the disruption. For GRB 250702B, these parameters apparently conspired to produce a 7-hour gamma-ray outburst.
Intermediate-Mass Black Holes: A Missing Link?

The discovery of GRB 250702B has revived scientific interest in intermediate-mass black holes (IMBHs)—black holes with masses between roughly 100 and 100,000 solar masses. IMBHs occupy a mysterious region of parameter space: they are much more massive than stellar-mass black holes produced by stellar collapse but far less massive than supermassive black holes found at galaxy centers. The formation channels for IMBHs remain uncertain. They could form through hierarchical mergers of stellar-mass black holes in dense stellar systems, through runaway stellar collisions in young star clusters, or through other exotic mechanisms. Despite their theoretical motivation and plausible formation pathways, IMBHs have proven frustratingly elusive to identify definitively. Few unambiguous IMBH detections exist, leaving their demographics and role in the universe poorly constrained. The tidal disruption scenario for GRB 250702B suggests one pathway for IMBH discovery. A star tidally disrupted by an IMBH could produce a distinct gamma-ray signature—an extended duration GRB with multiple episodic bursts. If additional ultra-long GRBs with similar properties are discovered, they could provide a census of the IMBH population and reveal their prevalence in galaxies. This would have profound implications for understanding black hole formation and the assembly of massive black holes through cosmic time.

Discussion: Gravitational Waves, Multi-Messenger Astronomy, and Future Implications

Gravitational Wave Precursors: Detecting the Inspiral

A fascinating implication of GRB 250702B's tidal disruption interpretation is the potential for gravitational wave detection. As a star spirals inward toward a black hole due to gravitational radiation losses, the changing orbital quadrupole moment radiates gravitational waves—ripples in spacetime that propagate outward at light speed. The frequency and amplitude of these gravitational waves depend on the black hole's mass, the star's mass, and the orbital separation. For a stellar-mass black hole and a star, the gravitational wave signal could potentially be detectable by gravitational wave observatories like LIGO and Virgo, particularly if the inspiral occurs over timescales long enough (hours or longer) to remain within the sensitive frequency band of these instruments. GRB 250702B's 7-hour duration suggests an inspiral timescale potentially compatible with LIGO/Virgo sensitivity. If gravitational waves from a tidal disruption event were detected, it would represent a major breakthrough: a direct confirmation of the tidal disruption mechanism and potentially the first evidence for a black hole-star system in gravitational waves. Such a detection would usher in a new era of multi-messenger astronomy, with simultaneous observations of electromagnetic radiation (gamma rays, X-rays, optical) and gravitational waves from the same cosmic event.
Population Statistics and the Missing IMBH Question

The discovery of GRB 250702B's apparent tidal disruption origin raises profound questions about black hole populations across the universe. How many stellar-mass black holes exist in galaxies, and what fraction are in close binary systems with stars? How many IMBHs populate galaxies, and what are their formation channels? How common are tidal disruption events, and what fraction produce jets capable of generating gamma-ray bursts? These questions can be addressed statistically through surveys that discover additional ultra-long GRBs and characterize their properties. Future all-sky surveys, particularly the Vera C. Rubin Observatory's Legacy Survey of Space and Time beginning in 2026, are expected to discover transient events at unprecedented rates. Among these discoveries will be additional long-duration gamma-ray bursts and tidal disruption events. By accumulating statistics on these events—their durations, host galaxies, distances, and follow-up properties—astronomers can constrain the black hole population and the rates of tidal disruption events across cosmic time.
Rethinking Stellar Death and Black Hole Physics

GRB 250702B's discovery forces a reconsideration of our understanding of stellar death and black hole accretion physics. For decades, theoretical astrophysicists developed sophisticated models of stellar core collapse, neutron star mergers, and accretion onto black holes. These models have proven remarkably successful at explaining the vast majority of observed gamma-ray bursts and transient phenomena. Yet GRB 250702B demonstrates that the universe is richer and more complex than existing paradigms encompass. The discovery motivates new theoretical work on tidal disruption physics, magnetic reconnection in accretion disks, relativistic jet formation, and the extreme physics of black hole-star interactions. Laboratory experiments in high-energy-density physics and supercomputer simulations may help illuminate the processes occurring in these cosmic catastrophes. Simultaneously, observational campaigns coordinating gamma-ray, X-ray, optical, infrared, and radio observations can provide comprehensive multi-wavelength views of future tidal disruption events, testing theoretical predictions against observations.

Conclusion: A New Category of Cosmic Violence

GRB 250702B, the longest gamma-ray burst ever observed, represents far more than a record-breaking achievement in transient astronomy. It opens a fundamentally new window on extreme physics—the violent tidal disruption of stars by black holes and the catastrophic release of energy when a black hole consumes a star over timescales of hours. The discovery challenges existing theoretical models of gamma-ray burst formation and forces the astronomical community to expand its understanding of how some of the most energetic phenomena in the universe are produced. The tidal disruption interpretation raises tantalizing possibilities: the detection of gravitational waves from black hole-star inspirals, the discovery and characterization of intermediate-mass black holes through their tidal disruption signatures, and the revelation of new astrophysical processes occurring in the extreme gravity regime near black hole event horizons. As advanced observatories like the Vera C. Rubin Observatory, the Einstein Probe, and next-generation gamma-ray and gravitational-wave detectors scan the skies in coming years, the expectation is that additional ultra-long gamma-ray bursts and tidal disruption events will be discovered. Each discovery brings us closer to a complete census of black hole populations and populations, and a deeper understanding of how gravity shapes the universe's most violent phenomena. GRB 250702B stands as a milestone: a reminder that even after millennia of astronomical observation, the universe still holds profound surprises waiting to transform our understanding of reality.