Considering the immense size of the universe, it's no surprise that space still holds plenty of secrets for us. Recently, astronomers believe they stumbled upon a kind of cosmic blast never seen before, challenging our understanding of how stars die. In a paper available on the arXiv preprint server, scientists report the longest gamma-ray burst (GRB) ever recorded. This unique event was spotted by NASA's Fermi telescope on July 2, 2025, and is designated as GRB 250702B.
Gamma-ray bursts are recognized as the most powerful and violent explosions in the universe. Typically, these events last anywhere from a few milliseconds to several minutes. They occur when the core of a massive star collapses into a black hole or when two compact objects, such as black holes or neutron stars, merge. When these GRB events happen, they can be incredibly bright, often briefly outshining entire galaxies.
However, GRB 250702B exhibited an extraordinary behavior by flaring up for an entire day. In contrast, normal cosmic explosions only occur once—it's impossible for a star to explode twice. This prompted astronomers to investigate further. To understand the phenomenon better, they needed to determine its distance, which would aid in calculating its energy and narrowing down possible causes.
The team employed the powerful James Webb Space Telescope to ascertain the distance of GRB 250702B. By integrating this measurement into energy calculations, they discovered that it was the most energetic cosmic explosion ever recorded. Typically, long gamma-ray bursts accompany a massive supernova, so the astronomers searched for one nearby. However, they did not find a bright supernova; a fainter one may be obscured by the dust of the host galaxy.
Observations have confirmed that GRB 250702B is surprisingly distant, given the observed brightness of its host galaxy. The associated energy release is substantial enough to strain, but not definitively break, the canonical GRB collapsar models, as the researchers articulate in their findings.
The authors of the study speculate that GRB 250702B may have been caused by either a very unusual form of a collapsing star or a black hole destroying a smaller star. An additional surprising discovery was that the host galaxy is both extremely large and incredibly dusty. Typically, GRBs occur in small, young star-forming galaxies. This raises the question of whether the environment played a crucial role in creating this unique GRB, as the astronomers point out in their paper.
The identification of such an exotic GRB in a peculiar galaxy opens the door to new possibilities regarding its progenitor channel. The authors conclude that the environment likely had a significant impact on the creation of GRB 250702B. As researchers continue their work, there remain numerous mysteries to unravel, including the search for the hidden supernova, long-term monitoring of the GRB's afterglow, and the development of new models to explain this rare cosmic event.
In summary, the discovery of GRB 250702B not only challenges existing theories about gamma-ray bursts but also emphasizes the complexities of stellar evolution and the environments in which these extraordinary events occur. The ongoing research into this remarkable cosmic phenomenon promises to enhance our understanding of the universe.