Astronomers investigating mysterious X-ray flashes believe these explosions could be caused by collisions between neutron stars, the events that forge elements such as gold, silver and platinum. The event, called EP250704a, was first seen on July 4, 2025, as a gamma-ray burst that lasted half a second, followed by a bright X-ray emission that lasted 10 minutes. After receiving an alert from the joint European-Chinese Einstein probe that witnessed the explosion, a team of astronomers began searching for its cause by studying the aftermath of the explosion using the Very Large Telescope (VLT), the Very Large Array (VLA) and other telescopes of the European Southern Observatory. According to astronomer Niccolò Passaleva, who led observations of the X-ray flare with the VLT, this cosmic burst was unlike any scientist had seen before. “This is the longest-lasting X-ray flare ever observed in a neutron star merger,” Passaleva said in a statement. “It’s an opportunity to have a front-row seat to the most extreme forces in the universe and discover more of its secrets.” Neutron stars are created when massive stars die in supernova explosions, packing one or two masses of the sun into a width similar to that of a city on Earth and creating material so dense that a single teaspoon of neutron star matter brought to Earth would weigh 10 million tons. When these extreme dead stars collide with each other, they create environments so turbulent and violent that they are capable of forging elements so heavy that not even the hearts of stars can. Elements like gold on the finger. These collision and merger events, marked by flashes of light called kilonovae, have long been associated with flashes of high-energy gamma rays that disappear within two seconds, but new research suggests that some neutron star mergers could be revealed through X-ray bursts that last minutes. In particular, scientists have wondered whether neutron star mergers could be the cause of hundreds of X-ray flares in distant galaxies discovered by the Einstein probe since its launch in 2024. While some of these have been linked to the explosive death of supernovae of massive stars that can create a neutron star or black hole, others have defied explanation. EP250704a is one such X-ray flare. “When I saw the X-ray data from this new event, I realized something was up,” team member Eleonora Troja, part of the European Einstein Probe collaboration, said in the statement. The team believes there is something special about the neutron star merger mix that results in these X-ray bursts. EP250704a, an X-ray event suspected to be a neutron merger. (Image credit: Niccolò Passaleva, Eleonora Troja (ERC BHianca), ESO/VLT)Fusion with a magnetarAll neutron stars are created in the same way from the collapse of the core of a massive star, but not all neutron stars are the same. Just as an ice skater pulls on his arms to increase the speed of a spin, the rapid reduction in radius of a collapsing stellar core can “speed up” the rotation of a neutron star to more than 700 times per second. This collapse may also have another consequence. What to read next It turns out that magnetic fields get stronger when the magnetic field lines get closer together. That means the collapse of a stellar core with an already powerful magnetic field can create a neutron star with the strongest magnetic field in the universe. These neutron stars have a special name: magnetars. An illustration shows a magnetar surrounded by green magnetic field lines (Image credit: Robert Lea (created with Canva)) The team behind this research believes that the neutron star merger in question involved at least one magnetar. “If the remnant of the collision is a magnetar, it could continue to explode for longer,” Troja said. “Magnetars are rapidly spinning neutron stars with huge magnetic fields. When they discharge their magnetic power into the environment, they can make any explosion brighter and longer lasting.” An illustration of the Einstein probe detecting a cosmic explosion caused by two colliding neutron stars (Image credit: Science Bulletin (2026)) The researchers ruled out a supernova as the cause of the X-ray burst and were also able to determine that light from this collision has been traveling to Earth for 6 billion years. Discovering more of these extreme X-ray flashes could help astronomers determine how often magnetars form through these neutron star mergers, Passaleva said in the statement. The team’s research was published in the journal Science Bulletin.
