Unusual 10-Minute Cosmic Burst Offers Clues to Magnetar Formation: Astronomers Study 6 Billion-Year-Old Signal

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The Einstein Probe observed a rare cosmic burst featuring a short gamma-ray flash followed by prolonged X-ray emission, possibly from merging neutron stars forming a magnetar.

On July 4, 2025, the space observatory Einstein Probe detected a distinctive cosmic burst originating approximately six billion years ago. The event, designated EP250704a, began with a brief gamma-ray flash lasting about half a second, succeeded by an intense X-ray emission that intriguingly persisted for around ten minutes. This unusually long duration prompted an international team of astronomers to investigate its origin.

Subsequent observations utilizing multiple instruments—including the Very Large Telescope (VLT) of the European Southern Observatory and the Very Large Array (VLA) radio telescope—helped gather more data on the phenomenon. According to astrophysicist Niccolò Passaléva, who led the observations with the VLT, such a prolonged initial X-ray emission in the context of neutron star mergers has not been seen before.

Neutron stars are compact remnants of massive stars that have undergone supernova explosions. Despite their small diameter of a few tens of kilometers, they can possess masses surpassing that of the Sun. When two neutron stars collide, the event triggers extreme temperatures and intense particle outflows, also producing heavy chemical elements like gold, silver, and platinum. These explosive events are termed kilonovae.

The prolonged X-ray emission observed is hypothesized to result from the formation of a magnetar—a highly magnetized, rapidly spinning neutron star—following the merger. Such a magnetar could inject energy into the surrounding material over an extended period, sustaining the X-ray brightness beyond the initial burst phase. Researcher Eleonora Troja explained that a magnetar remnant can continue generating flares for a longer time due to the release of magnetic energy, enhancing the event's luminosity and duration.

While alternative explanations, such as a supernova explosion, were considered, the observational data did not support those scenarios. The researchers conclude that the most plausible cause of EP250704a is the merger of neutron stars, with magnetar formation remaining a compelling but still unconfirmed hypothesis requiring further study.

This discovery sheds light on the nature of other enigmatic X-ray bursts recorded by the Einstein Probe since its 2024 launch. Although some bursts have been linked to massive star explosions, many remain unexplained, and insights from EP250704a could help unravel these cosmic mysteries.