OrbitalHub

Mea AI adiutor dicit:

In the early hours of July 2, 2025, astronomers around the world were startled by an astonishing signal: a burst of extremely energetic gamma-rays originating from a distant galaxy approximately 8 billion light-years away in the constellation Scutum. This event, designated GRB 250702B, is not just another gamma-ray burst (GRB) — it turned out to be the longest and most unusual gamma-ray explosion ever observed, challenging decades of understanding about how these cosmic events work. Rather than fading within seconds or minutes like typical GRBs, GRB 250702B continued to flash in gamma-rays and X-rays for hours, possibly extending nearly a full day in total activity, punctuated by multiple bursts separated by regular intervals — behavior never before seen in the cosmic fireworks of the universe.

Gamma-ray bursts themselves are among the most powerful explosions known. They release more energy in a blink of an eye than the Sun will emit over its entire 10-billion-year lifetime. Astronomers classify GRBs into two broad categories: short bursts lasting less than about two seconds, typically associated with the merger of compact objects like neutron stars or black holes; and long bursts, usually tied to the catastrophic collapse of a massive star’s core into a black hole or neutron star at the end of its life. In both cases, collapsing matter drives ultrarelativistic jets — beams of particles moving at nearly the speed of light — that produce gamma rays when they interact with surrounding material. These jets, narrowly focused and extremely bright, can be detected across vast cosmic distances, briefly outshining entire galaxies.

What set GRB 250702B apart was not only its **extraordinary duration — around seven hours in gamma-rays with associated X-ray activity detected even earlier — but also the fact that the burst appeared to repeat multiple times over that period. Traditional GRB models involve a one-time, catastrophic event that destroys the progenitor star, meaning the central engine powering the burst should cease after a singular explosion. In contrast, GRB 250702B produced distinct pulses spaced quasi-periodically over hours, an anomaly that pushed researchers to consider more exotic origins. Telescopes including NASA’s Fermi Gamma-ray Space Telescope and the Chinese Einstein Probe first recorded the unusual emission, later confirmed by follow-up observations from space and ground-based facilities that tracked the afterglow across the electromagnetic spectrum.

One of the leading interpretations emerging from this unprecedented data is that GRB 250702B may not fit neatly into the classic “collapsar” model for long GRBs — the collapse of a single massive star. Instead, astronomers have explored scenarios involving tidal interactions between a black hole and a companion star. In one compelling model consistent with both the timing and periodicity of the pulses, a stellar-mass black hole — perhaps just a few times the mass of the Sun — was in a tight orbit with a companion star. Over time, this black hole spiraled into the star’s outer layers and then its dense core, slowly shredding and consuming the stellar material from within. As it tore through the star, enormous amounts of gas would have accreted onto the black hole, fueling sustained jets of gamma-ray-emitting plasma over many hours, rather than the brief flash typical of ordinary GRBs. While this “black hole eating a star from within” picture remains theoretical, it provides a framework for the extended engine activity and repeating pulses seen in GRB 250702B, and could represent a new class of gamma-ray transient.

Alternative explanations have also been proposed. Some researchers have suggested that the long emission could be produced by a tidal disruption event (TDE), where a black hole — potentially larger than a stellar-mass black hole — comes close enough to a star to rip it apart through extreme gravitational forces. The debris from the disrupted star could feed the black hole over extended periods, powering a prolonged gamma-ray and X-ray signal. Others have proposed models involving magnetic jets with precession — a wobbling motion caused by misalignment between the black hole’s spin and the accretion disk — that could produce repeated pulses spaced at regular intervals as the jet sweeps across our line of sight. New work from theoretical astrophysicists suggests that the structure and timing of the emissions from GRB 250702B can be explained by such a precessing magnetic jet engine, offering a coherent explanation for the “heartbeat-like” nature of the burst.

Beyond the theoretical intrigue, GRB 250702B is significant because it highlights how cosmic explosions can transcend familiar categories, revealing physics and astrophysical environments more complex than previously understood. This event not only broke records for duration, but also offered the first case where a gamma-ray source exhibited multiple, spaced bursts over hours, suggesting a central engine that remained active far longer than classic models predict. Continued analysis of the afterglow — the fading light across X-ray, optical, and radio wavelengths — and characterization of the host galaxy will help astronomers distinguish between rival models and refine our understanding of these powerful cosmic beacons. With each new observation, events like GRB 250702B deepen our grasp of how matter and energy behave under the most extreme conditions and remind us that the universe still holds phenomena that challenge existing theories.

Video credit: NASA/LSU/Brian Monroe, Animator: Brian Monroe, Producer: Scott Wiessinger (eMITS), Science Writer: Francis Reddy (University of Maryland College Park), Scientist: Eric Burns (LSU)