A half-second gamma-ray blast followed by a 10-minute X-ray surge from a galaxy 6 billion light-years away may mark two dead stars smashing together, and astronomers say it is unlike anything they have seen.
The event, labeled EP250704a, was first spotted on July 4, 2025, when the joint European-Chinese Einstein Probe caught a brief gamma-ray burst and then a bright X-ray glow that kept going for a full 10 minutes. Space.com reported that a research team studying the aftermath now believes the signal came from a neutron-star merger, possibly leaving behind a magnetar, and has ruled out a supernova.
That long X-ray phase is the headline anomaly. Ordinary gamma-ray flashes tied to these crashes usually vanish within two seconds. This one refused to quit.
Astronomer Niccolò Passaleva, who led follow-up work with the European Southern Observatory’s Very Large Telescope, put the finding in plain terms.
"This is the longest-lasting prompt X-ray flash ever observed from a neutron star merger."
He and colleagues also used the Very Large Array and other telescopes to track what the blast left behind. Their research has been published in the journal Science Bulletin.
The Einstein Probe, launched in 2024, has already flagged hundreds of X-ray flashes in distant galaxies. EP250704a stood out. Light from the collision had been traveling toward Earth for 6 billion years before the alert went out.
Team member Eleonora Troja, part of the Einstein Probe’s European collaboration, said the X-ray data alone raised red flags.
"When I saw the X-ray data from this new event, I realized something was up."
The working theory is a merger of neutron stars, the ultra-dense cores left when massive stars die. Pack the mass of the sun, or even two suns, into a width no larger than a city. Spin one of those remnants more than 700 times a second. A single teaspoon of that matter, brought to Earth, would weigh about 10 million tons.
When two of them collide, the crash can power a kilonova and a short gamma-ray burst. If the leftover object is a magnetar, a neutron star with an extreme magnetic field, the fireworks can last longer.
"If the remnant of the collision is a magnetar, it could keep bursting for longer. Magnetars are rapidly spinning neutron stars with huge magnetic fields. When they dump their magnetic power into the surroundings, they can make any explosion brighter and longer-lasting."
That magnetic dump is the cleanest explanation the team has for a prompt X-ray flash that stretched across 10 minutes instead of blinking out in seconds. Supernova models did not fit the data they collected after the Einstein Probe’s alert.
Passaleva framed the detection as more than a one-off curiosity. Finding more events like EP250704a could show how often magnetars form when neutron stars merge, a basic rate that still sits in the “unknown” column of astrophysics.
"It is an opportunity to have a front-row seat to the most extreme forces of the universe and discover more of its secrets."
The host galaxy itself remains unnamed in the public article. Exact fluxes, confidence levels, and the full author list sit in the Science Bulletin paper rather than the news account. What is solid is the sequence: short gamma spike, stubborn X-ray afterglow, multi-telescope follow-up, supernova ruled out, neutron-star merger with a possible magnetar remnant left on the table.
In other words, instruments built by free societies and international partners just watched two of the densest objects in creation finish a collision that began when the light now reaching us first left its galaxy. The universe still runs on hard rules. Good observers keep finding them.
