Astronomers have recently documented the longest gamma-ray burst (GRB) ever observed, named GRB 250702B. This massive explosion lasted about 7 hours, far exceeding the duration of previous bursts. Discovered on July 2, 2025, by NASA’s Fermi telescope, this event is sparking significant interest in the astronomical community.
Gamma-ray bursts are the most intense explosions in the universe. They can outshine entire galaxies in mere moments. Most GRBs occur when a massive star collapses into a black hole, causing a brief but powerful light show. Some, known as ultra-long GRBs, last longer than 1,000 seconds. GRB 250702B shattered the previous record holder, GRB 111209A, lasting an incredible 25,000 seconds.
According to astrophysicist Daniel Perley from Liverpool John Moores University, GRB 250702B looks different from any other observed burst. The team speculates that a black hole crashed into a companion star, fueling jets from deep within. As the black hole descends into the star, it creates an accretion disk—a swirling mix of gas that can launch jets of energy. One possible source of this energy is the Blandford-Znajek mechanism, which harnesses the black hole’s spin through magnetic fields.
Key features of GRB 250702B include rapid flickers lasting about a second, indicating a smaller engine than typical supermassive black holes. Observations showed photons in the multi-MeV range, suggesting that the jets were moving at amazing speeds, nearly reaching the speed of light.
Follow-up studies from the Webb Telescope confirmed these findings. It measured a redshift of 1.036, allowing scientists to estimate its distance and energy. Intriguingly, they found no signs of a supernova at the location of the burst, contradicting the expectation that such events usually occur when a supermassive black hole shreds a nearby star.
Understanding what leads to long GRBs like 250702B is crucial. Ordinary GRBs are short-lived due to the rapid collapse of a single star. In contrast, long GRBs often result from the merger of two compact objects, such as neutron stars or black holes, which collide after billions of years. This merger typically produces a burst that lasts less than two seconds.
However, GRB 250702B’s long duration may result from a black hole slowly consuming material from a companion star. The absence of a bright supernova in follow-up studies aligns with this theory, suggesting that if there was an explosion, it was faint or obscured by dust.
Further research is needed to clarify the mechanisms behind GRB 250702B. If helium mergers drive ultra-long bursts, they might favor star-rich, dust-filled regions. These kinds of events can be difficult to detect due to their gradual evolution and relatively low brightness.
The upcoming Rubin Observatory will accelerate efforts to monitor the sky, improving our chances of capturing these rare phenomena. With its ability to observe rapidly, it could provide vital data for future investigations into GRBs.
For now, GRB 250702B does not change our entire understanding of gamma-ray bursts, but it challenges existing ideas while hinting at new possibilities. The combination of different observational tools, including gamma rays, X-rays, and infrared data, has been essential in this endeavor. Continued study will reveal more about this remarkable burst and deepen our understanding of the universe’s most powerful explosions.
The findings regarding GRB 250702B are detailed in a study published on arXiv, allowing others in the scientific community to explore this extraordinary event further.
