A Record-Breaking X-Ray Flash May Reveal the Birth of a Magnetar

Astronomers may have witnessed the birth of an extraordinary cosmic object after two neutron stars collided more than 6 billion years ago.

The event produced a burst of gamma rays that lasted less than a second. But something much longer followed: an intense X-ray flash that remained visible for nearly 10 minutes.

Scientists say the observation provides strong evidence that the collision created a magnetar, a rapidly spinning neutron star with an extremely powerful magnetic field.

A Cosmic Explosion That Kept Glowing

The event, known as EP250704a/GRB 250704B, was detected on July 4, 2025, by several space observatories, including the Einstein Probe, SVOM and Insight-HXMT satellites.

At first, the event looked similar to other short gamma-ray bursts associated with collisions between neutron stars. The gamma-ray emission lasted only about half a second.

However, the Einstein Probe detected bright X-ray emission for almost 10 minutes. Researchers say this is the longest-lasting prompt X-ray flash ever observed from a neutron star merger.

Scientists Chased the Signal

After receiving the alert, researchers quickly organized follow-up observations using powerful ground-based telescopes, including the European Southern Observatory’s Very Large Telescope in Chile.

Niccolò Passaleva, who led the follow-up observations, began working on the event while traveling home by train. The rapid response allowed astronomers to observe the fading explosion while it was still bright enough to study in detail.

The researchers separated the light from the explosion into its individual wavelengths. This revealed patterns that allowed them to determine that the event occurred at a distance corresponding to more than 6 billion years of travel time for its light to reach Earth.

No Supernova Was Found

The team also searched for evidence of a supernova.

If the long-lasting X-ray flash had been produced by the death of a massive star, astronomers would normally expect to see a powerful stellar explosion. But their observations did not reveal a supernova.

Combined with the measured distance and other properties of the event, the evidence instead pointed toward a collision between two neutron stars.

A Possible Birthplace of a Magnetar

Neutron stars are the extremely dense remnants left behind after massive stars die. When two neutron stars merge, they can produce gravitational waves and intense bursts of radiation.

In some cases, the merger may leave behind a magnetar. These objects spin rapidly and possess extraordinarily strong magnetic fields. As the magnetar loses some of its rotational and magnetic energy, that energy can continue powering bright radiation after the initial collision.

The researchers believe this could explain why the X-ray emission from EP250704a lasted far longer than the initial gamma-ray burst.

A New Way to Search for Cosmic Collisions

The discovery could give astronomers another way to identify neutron star mergers.

Scientists have traditionally relied heavily on short gamma-ray bursts and gravitational-wave signals to study these violent events. If similar long-lasting X-ray flashes are found in the future, they could provide another valuable signal.

Researchers hope future gravitational-wave observations can eventually be matched with these unusual X-ray flashes, allowing scientists to study the same cosmic collision through both gravitational waves and light.

Sources

• ScienceDaily — “A record-breaking X-ray flash may reveal the birth of a magnetar” — September 30, 2026.
• European Research Council / EurekAlert! — “Astronomers link mysterious cosmic flashes to collisions of dead stars” — September 30, 2026.
• Nanjing University School of Astronomy and Space Science — “Minutes-long Soft X-ray Prompt Emission from a Compact Object Merger” — September 30, 2026.
• Science Bulletin — “Minutes-long soft X-ray prompt emission from a compact object merger” — 2026.