Astronomers have uncovered compelling evidence that some mysterious X-ray flashes lasting several minutes could be produced by collisions between neutron stars, offering a new way to identify some of the most violent events in the Universe.
The research, published in Science Bulletin, suggests that neutron star mergers — traditionally identified through brief gamma-ray bursts — may also generate much longer X-ray emissions when the collision creates an intensely magnetic stellar remnant known as a magnetar.
Mysterious X-Ray Flashes Offer New Clues
Since the Einstein Probe satellite was launched in January 2024, astronomers have detected hundreds of bright X-ray flashes originating from distant galaxies. Known as fast X-ray transients, some have been associated with the deaths of massive stars, while the origins of others have remained uncertain.
Researchers working with Professor Eleonora Troja, supported by a European Research Council Consolidator grant, obtained crucial observations of one such transient after receiving an alert from Einstein Probe.
The team rapidly coordinated observations using other facilities, including the European Southern Observatory’s Very Large Telescope (VLT) in Chile and the Very Large Array. Their findings indicate they may have witnessed the birth of a magnetar following the merger of two neutron stars.
Record-Breaking X-Ray Flash Detected
Neutron stars are extraordinarily dense stellar remnants formed after massive stars reach the end of their lives. When two neutron stars collide, the event can generate gravitational waves that travel across space, while accompanying electromagnetic radiation provides information about what remains after the merger.
Short gamma-ray bursts have long been one of the primary indicators of neutron star collisions.
“However, if the remnant of the collision is a magnetar, it could keep bursting for longer” said Prof. Troja, who is part of the Einstein Probe European collaboration and co-corresponding author of the paper.
“Magnetars are rapidly spinning neutron stars with huge magnetic fields. When they damp their magnetic power into the surroundings, they can make any explosion brighter and longer-lasting. When I saw the X-ray data from this new event, I realized something was up.”
The event, designated EP250704a/GRB 250704B, was discovered on 4 July 2025 by the SVOM, Insight-HXMT and Einstein Probe satellites.
Its gamma-ray burst lasted only about half a second. However, Einstein Probe recorded bright X-ray radiation continuing for almost 10 minutes.
“This is the longest lasting prompt X-ray flash ever observed from a neutron star merger,” said graduate student Niccolò Passaleva, who led follow-up observations using the VLT in Chile.
“It is an opportunity to have a front-row seat to the most extreme forces of the Universe and discover more of its secrets.”
Rapid Telescope Observations Reveal the Burst’s Distance
Astronomers had spent several years searching for a convincing connection between fast X-ray transients and neutron star mergers. Previous candidates faded before researchers could gather enough evidence to establish their origins.
This event provided a different opportunity. Passaleva responded within minutes, allowing observations to begin while the explosion remained bright enough for detailed study.
“I was traveling home by train,” recalls Passaleva, “and all of a sudden I was rushing against time to commandeer one of the largest telescopes in the world from my laptop.”
Using the VLT’s X-Shooter instrument, researchers separated the incoming light into its individual components and detected absorption patterns that enabled them to calculate the event’s redshift and therefore its distance.
The measured redshift of z=0.6610 showed that the explosion occurred before the formation of the Sun and its planets. Its light travelled for more than six billion years before reaching Earth.
Absence of Supernova Strengthens Merger Evidence
Researchers also used deep observations from the VLT’s FORS2 instrument to search for evidence of a bright supernova.
Such an explosion would normally be expected if the long-lasting X-ray emission had resulted from the collapse of a massive star. No supernova was detected.
The combination of the measured distance, the absence of a supernova and the characteristics of the burst provided strong evidence that the event originated from a neutron star merger rather than a massive star collapsing.
Future Observations Could Confirm Magnetar Formation
Scientists say discovering additional events of this type could help determine how frequently neutron star mergers produce magnetars.
“Finding more of these X-ray flashes could help reveal how often neutron star mergers create magnetars,” concludes Passaleva, “I am really excited for the next run of gravitational wave observations, when we could finally pair one of these X-ray flashes with a burst of gravitational waves from the same source.”
The research involved an international collaboration of astronomers from institutions including Beijing Normal University, the Chinese Academy of Sciences, the University of Rome Tor Vergata, Nanjing University and the University of Hong Kong.
Future gravitational-wave observations, combined with rapid X-ray and optical follow-up, could provide scientists with a clearer picture of what happens immediately after neutron stars collide and whether magnetars commonly emerge from these extreme cosmic events.
Cory Weinberg is a contributor to Sproutwired.com, covering a wide range of topics including news, politics, business, technology, sport, entertainment and lifestyle. He focuses on delivering clear, balanced reporting that helps readers stay informed about current events and emerging developments. Cory’s work highlights relevant stories, practical insights and important issues affecting communities and industries, with an emphasis on accuracy, clarity and information that readers can trust.
