Astronomers have revealed that a strange cosmic flash, the longest of its kind ever seen, was probably created by two dead stars crashing together.
The colossal explosion appears to have led to the creation of a magnetar – a dead star with among the strongest magnetic fields known in the Universe, a trillion times that of Earth – according to a study recently published in Science Bulletin.
The bright flash initially mystified astronomers when it was detected by three different satellites in July 2025, coming from a galaxy billions of light-years away.
Two of these satellites saw a gamma-ray burst lasting just 0.4s, suggesting an extreme cosmic event. The third observatory looked in X-rays.
“Through the X-ray lens, the event looked completely different: it kept bursting for [almost 10] minutes,” said Prof Eleonora Troja of the University of Rome Tor Vergata, who helped observe the event.
Troja and her team initially thought the explosion could be from a giant star dying in a supernova and quickly deployed the world’s best telescopes looking for signs of one.
“None appeared,” said Troja. “That absence was an important clue that we had witnessed a collision of neutron stars.”
Neutron stars are the superdense remnants left behind after a star goes supernova. The length of the X-ray flash is probably due to what was created after the collision.
“We think that in this case, a newborn magnetar was likely responsible for the X-ray flash,” said Troja.
The magnetar’s potent magnetic field would interact with its surroundings, amplifying the cosmic explosion so it burns brighter and lasts longer.
“When neutron stars collide, they create one of the most extraordinary laboratories to test the laws of physics with extremely high temperatures and insanely high densities,” said Troja.
“These gamma and X-ray flashes are our window into this laboratory. While the gamma-ray flash vanishes in less than two seconds, the X-ray flash goes on for much longer and this gives us more time to learn what happens during those first critical minutes after the collision.”
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