Astronomers have captured the longest gamma ray burst ever observed, a seven-hour burst of intense light from a black hole devouring a companion star.
The event, called GRB 250702B, lasted about 25,000 seconds, breaking the previous record of 15,000 seconds and forcing scientists to rethink how the most powerful explosions in the universe work.
Gamma ray bursts are short, intense bursts of high-energy radiation that usually last from a fraction of a second to a few minutes. They are driven by jets traveling at nearly the speed of light, produced when a massive star collapses or when two dense interstellar remnants collide.
To most of us, they are distant fireworks, but to astronomers they are one of the best tools for investigating how stars live and die far away in the universe.
Holding a burst of seven hours
So what made this event so unusual? For starters, its full length. Based on combined data from several space-based detectors, scientists estimate that the gamma ray component of GRB 250702B lasted about twenty-five thousandths of a second.
In comparison, a typical long gamma ray burst evaporates after tens of seconds, and even the first record holder, GRB 111209A, “only” remained bright for about fifteen thousandths of a second.
The signal also appeared in several separate bursts, seen multiple times by the Gamma ray Burst Monitor aboard the Fermi Gamma ray Space Telescope and other instruments. The method told the researchers that they were not seeing a series of unrelated events, but one long-term engine turning on and off while feeding nearby fuel.
From collapsing stars to cosmic outliers
To date, most long-range gamma-ray bursts have been explained by two main scenarios. In the first case, a massive, rapidly spinning star collapses into a black hole, sending out thin jets that pierce the dying star and light up the sky.
In the second, two neutron stars or a neutron star and a black hole orbit and collide, also driving a short, violent flight.
Both of these methods can produce large amounts of energy, but are limited by how much material can fall and how fast. Even in extreme cases, models suggest that the engine should shut down after several thousandths of a second.
GRB 250702B has continued to pass for much longer than that, and in less than a second it points to a compact, star-heavy object at its center instead of the supermassive black hole in the galactic center.
That left astronomers in an interesting spot. The explosion seemed to come from a stellar black hole, but its timing didn’t follow the usual recipe.
A black hole collapses into a star
The new study, led by Eliza Neights of NASA’s Goddard Space Flight Center, argues that the best explanation is the so-called fusion of helium.
In this case, a black hole with about the mass of the star orbits a star that is a helium star that has lost its outer hydrogen components. As a helium star expands at the end of its life, the black hole spirals inward, dives into the star’s envelope and begins to tear it apart.
When that happens, a large amount of orbital angular energy is thrown into the falling material. Instead of crashing directly into the black hole, the gas forms an expanding disc that can feed the central engine for hours. The result is a long-lived, ultra-relativistic jet that we see as bursts of very long-range gamma rays.
For GRB 250702B, recent observations in X-ray, infrared and radio have shown light from a dusty, star-studded region in the distant interstellar region, far from its central black hole. The power of the jet looks normal for a long blast once you know how focused it was, but it spread out over a very long time.
The combination is naturally compatible with the fusion of helium, where the sum of the fuel is similar to the old collapsar, which has just been gradually given off. It also links this piece of the record to other events where gamma ray bursts and rare supernovae appear to coincide.
Why are we only seeing these giants now?
If helium fusion is possible, why haven’t we seen this long burst? Another reason is to look at bias. Most gamma ray monitors in space are designed to detect short, sharp rays that appear above the background noise.
Long bursts are very faint at any given time and can be obstructed by Earth blocking the view, so they are easy to miss or misclassify.
In this case, scientists were helped by a network of instruments, including the Konus Wind experiment far from Earth, X-ray scanners such as MAXI on the International Space Station, and even the Psyche gamma ray and neutron detector, which happened to be in the right place to see part of the event.
Putting all those pieces together was a bit like reconstructing a very long, very disjointed blackout of security cameras across the entire city.
Looking ahead, future missions such as the Compton Spectrometer and Imager (COSI) will be able to observe large cosmic waves with very stable conditions, making it possible to catch large bursts and study them in detail.
That’s good news not only for high-energy astronomers, but also for anyone interested in how elements are made and recycled in galaxies over the course of the universe, and how some of the universe’s mysterious energy sources fit into the bigger picture.
A new chapter in astrology
For now, GRB 250702B stands out as a rare but revealing light. It suggests that some massive stars in nearby binaries don’t just fall apart, but can end their lives in a dramatic final act where the black hole collapses into its companion and destroys it from the inside.
In practical terms, this means that our picture of how stars enrich the universe with heavy elements, and how often different types of cosmic explosions occur, is still incomplete.
A large, long burst like GRB 250702B could connect stories of ancient gamma-ray bursts, other unusual supernovae and even other sources of gravitational waves that astronomers on Earth are only beginning to detect.
That connection has already been shown in some of the more powerful explosions and mysterious remains reported in our pages.
The universe has been conducting these extreme experiments for billions of years.
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