New Model Explains Exceptionally Long Gamma-Ray Burst
Scientists are working to unravel the mysteries of gamma-ray bursts (GRBs), the most energetic explosions in the universe. Recent research from a team at the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS) has proposed a new model to explain an unusually long-duration gamma-ray burst, GRB 250702B, which challenged existing understanding of these cosmic events. This burst, observed beginning July 2, 2025, lasted an unprecedented 29 hours, far exceeding the typical duration of GRBs, which usually range from milliseconds to a few minutes. The extended emission and accompanying X-ray variations have sparked intense debate within the astrophysics community.
The research, published in the journal *The Astrophysical Journal Letters*, details a comprehensive analysis of observational data collected by space-based observatories, including the Insight-HXMT and GECAM satellites. Researchers studied data spanning 30 days around the time of the burst, revealing the remarkably prolonged gamma-ray emission. This discovery has prompted a re-evaluation of the processes that drive these powerful cosmic phenomena and the types of stars that can produce them. Understanding GRBs is crucial as they provide valuable clues about the evolution of stars, galaxies and the universe itself.
Unprecedented Duration and a Supermassive Star
GRB 250702B’s exceptional length immediately set it apart. Typically, GRBs are categorized as either short-duration or long-duration, based on their emission times. Short-duration bursts are generally linked to the merger of compact objects like neutron stars, while long-duration bursts are associated with the collapse of massive stars. However, GRB 250702B defied easy categorization, exhibiting a gamma-ray profile similar to ultra-long bursts but with a multiwavelength evolution that suggests a different origin. The team’s analysis identified distinct temporal variations in the accompanying X-ray radiation, leading them to hypothesize that the progenitor star was a supermassive star, significantly more massive than our Sun.
According to the new model, the collapse of such a massive star unfolds over a much longer timescale – potentially spanning decades – compared to the relatively rapid collapse of stars that typically produce GRBs. When a star exhausts its nuclear fuel, its core collapses, forming a black hole. This black hole rapidly devours the star’s inner material, generating relativistic jets that travel at speeds approaching the speed of light, and are the primary source of the gamma-ray burst. Following this initial phase, a slower accretion process occurs, producing additional jets that emit radiation. This extended accretion phase, the researchers believe, is responsible for the unusually long duration of GRB 250702B.
The Role of GECAM and Insight-HXMT
The ability to study GRB 250702B in such detail was largely due to the capabilities of the GECAM and Insight-HXMT satellites. The GECAM (Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor) project, funded by the Chinese Academy of Sciences, is designed to detect both gravitational waves and high-energy electromagnetic radiation, providing a wide-field view of the sky. Insight-HXMT (Hard X-ray Modulation Telescope) is a Chinese space observatory dedicated to observing the universe in hard X-rays. As reported by the Institute of High Energy Physics, GECAM-C provided an accurate measurement of the low-energy band spectrum of the burst, while Insight-HXMT covered the higher energy band where key spectral lines were observed.
The combination of data from these two instruments proved crucial. “GECAM-C provided an accurate spectral measurement for the full course of this burst, while Fermi/GBM could extend the spectrum to a higher energy band. They together can deliver a very wide range of spectrum measurement and line search,” explained Shaolin Xiong, a lead researcher from the Institute of High Energy Physics, in a statement. The detailed data allowed the team to identify and analyze the temporal variations in the X-ray emission, ultimately leading to the development of the supermassive star model.
Gamma-Ray Bursts: Cosmic Explosions and Their Significance
Gamma-ray bursts were first discovered in the 1960s by the Vela satellites, which were originally launched to detect nuclear explosions. Since then, hundreds of GRBs have been observed, and they remain one of the most fascinating and enigmatic phenomena in astrophysics. These bursts release an immense amount of energy in a short period, often outshining entire galaxies. According to a press release from the Chinese Academy of Sciences, GRBs are considered the most energetic explosion phenomena in the universe and offer important insights into the lives and deaths of stars, the formation of galaxies, and the evolution of the universe.
The study of GRBs helps scientists understand the extreme physics that occur in these events, including the behavior of matter at incredibly high densities, and energies. The discovery of the highest-energy gamma-ray line in the universe, at 37 million electron-volts, from the exceptionally bright GRB 221009A in 2022, further highlighted the importance of these events for probing the fundamental laws of physics. This line, detected by researchers using data from Fermi/GBM, represents the highest-energy spectral line feature ever emitted by a celestial object.
Implications for Future Research
The new model proposed to explain GRB 250702B has significant implications for future research on gamma-ray bursts. It suggests that the population of GRB progenitors may be more diverse than previously thought, and that supermassive stars may play a more significant role in these events. Further observations and theoretical modeling will be needed to confirm this hypothesis and to refine our understanding of the processes that drive long-duration GRBs.
The ongoing development of advanced gamma-ray telescopes, such as the planned Einstein Probe mission, will be crucial for detecting and studying these rare and extreme events. These next-generation instruments will provide even more detailed data, allowing scientists to probe the physics of GRBs with unprecedented precision. The continued investigation of these cosmic explosions promises to unlock new secrets about the universe and our place within it.
The next step in this research will involve further analysis of the data from GRB 250702B and comparison with other long-duration GRBs to identify common characteristics and refine the supermassive star model. Scientists will likewise be looking for similar events in the future to test the validity of the new hypothesis. The ongoing quest to understand gamma-ray bursts remains a central focus of astrophysical research, promising to reveal new insights into the most energetic phenomena in the cosmos.
If you’d like to learn more about gamma-ray bursts and the research being conducted in this field, you can visit the websites of the Institute of High Energy Physics of the Chinese Academy of Sciences and NASA’s Gamma-ray Burst Coordination Network. Share your thoughts and questions in the comments below.