Astronomers tie a 10-minute X-ray flash seen by Einstein Probe to merging neutron stars

The X-ray emission lasted about 1,200 times as long as the gamma-ray spike before it ^[16]. Neutron-star mergers, the collisions space.com credits with forging gold, silver and platinum ^[12], have long been associated with gamma-ray flashes that fade within two seconds ^[5]. Some new research suggests that mergers can also show up as X-ray blasts lasting minutes ^[6].

The long X-rays caught the team's attention early. "When I saw the X-ray data from this new event, I realized something was up," said Eleonora Troja, a member of the Einstein Probe European collaboration ^[15]. The team's explanation for the extra minutes is a magnetar. According to space.com, the researchers think at least one was involved in the merger ^[9].

A collapsing stellar core can spin the neutron star it leaves behind up to more than 700 rotations a second ^[13]. The collapse also squeezes the magnetic field lines together, which strengthens the field. A core that starts out strongly magnetised can end as a magnetar, the object with the strongest magnetic field in the universe ^[13]. Troja framed the idea as a conditional. "If the remnant of the collision is a magnetar, it could keep bursting for longer," she said. "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." ^[10]

We treat the merger as the team's best current interpretation. In space.com's account, the case rests on ruling out a supernova ^[8]. The account does not describe any positive sign of a merger in the VLT or VLA data, such as the kilonova light that marks these collisions ^[5].

Then there is the denominator. Since it launched in 2024, Einstein Probe has recorded hundreds of X-ray flashes in distant galaxies, and some have defied explanation ^[7]. EP250704a is one of them, a single event set against a count in the hundreds. It also came with a half-second gamma-ray burst ^[1]. On its own, then, it cannot show that an X-ray survey finds mergers a gamma-ray instrument would miss. If the merger reading holds, it does show that a merger can keep producing X-rays for 10 minutes ^[1].