Unprecedented Gamma-Ray Burst Lasts Seven Hours, Challenges Cosmic Theories

Gamma-ray bursts (GRBs) are intense sources of high-energy radiation. They were first detected in the 1960s by US military satellites, which initially interpreted the bright bursts as potential nuclear detonations on Earth. Over time, astronomers began to understand the cosmic origins and physical processes behind these events.

GRB 250702B: An Unprecedented Blast

In 2025, astronomers identified an unprecedented blast from space, designated GRB 250702B, which lasted for seven hours. Eliza Neights, a researcher at NASA Goddard Space Flight Center and a 'burst advocate' for the Gamma-ray Burst Monitor on NASA's Fermi Space Telescope, was on duty during the detection. The instrument recorded an unusual pattern: three gamma-ray bursts appearing to originate from the same celestial location.

A Record-Breaking Seven-Hour Event

GRB 250702B is the longest-lasting GRB ever recorded, enduring for approximately seven hours (25,000 seconds), demanding a novel physical explanation.

This extreme duration significantly surpasses the average GRB lifespan of several minutes and exceeds the previous record holder, which lasted around 15,000 seconds. This exceptional duration suggests a novel physical explanation is required, as it cannot be accounted for by the currently known origins of GRBs.

Understanding Typical Gamma-Ray Burst Origins

Two main processes are recognized as the origin of GRBs:

• Massive Star Collapse: Most GRBs result from the collapse of a rapidly rotating, massive star into a compact object, likely a black hole. This process generates powerful jets of radiation.
• Neutron Star Mergers: Other GRBs occur when two neutron stars, which are highly dense stellar remnants, orbit each other and eventually merge. This event also forms a compact object that produces detectable jets.

The Helium Merger Hypothesis for GRB 250702B

The most plausible explanation for the extended duration of GRB 250702B is a 'helium merger.' This phenomenon involves a stellar-mass black hole orbiting a helium star. Helium stars are characterized by the stripping away of their outer hydrogen layers, leaving a dense helium core. During phases of expansion, the orbiting black hole can become embedded within the stellar envelope, leading to rapid consumption of the star. The transfer of angular momentum to the black hole during this process is believed to generate a long-lasting jet.

Challenges and the Future of GRB Detection

GRBs with extreme durations may be less common than other GRB progenitors, and their detection is challenging for telescopes designed to identify short, bright signals. Their dimmer nature also limits the distance over which they can be observed. Eliza Neights is currently involved with preparing the Compton Spectrometer and Imager (COSI) telescope, scheduled for launch in 2027, to enhance its capability for detecting and analyzing extreme-duration GRBs. This research aims to facilitate further observations and a comprehensive understanding of the physical processes behind these unique cosmic events.