An X-ray flash lasting nearly ten minutes could be the signature of a newly formed magnetar after the collision of two neutron stars, just before collapsing into a black hole.
When two neutron stars merge, they can produce a brief gamma-ray burst. These explosions are among the most energetic phenomena observed in the Universe. Their main gamma-ray emission generally lasts only a fraction of a second to a few seconds before giving way to weaker signals.
The event studied displays unusual behavior. After a brief episode of gamma rays, astronomers detected soft X-ray emission persisting for several hundred seconds. Its duration, close to ten minutes, far exceeds that of the initial high-energy signal.
The researchers compared this emission with several possible scenarios. One involves the birth of a magnetar, a neutron star with an extremely intense magnetic field. Such an object can contain a large amount of energy associated with its rapid rotation and magnetic field.
After the merger, the new object would therefore not collapse immediately into a black hole. It could survive for several minutes and power the X-ray emission by gradually losing its energy, then potentially collapse into a black hole. The observed duration would then correspond to this brief phase of life before a possible later transformation.
This interpretation nevertheless remains a hypothesis. Astronomers did not observe the magnetar directly. They infer its possible presence from the duration, energy, and evolution of the radiation. Other mechanisms related to the merger debris may also contribute to the signal.
The significance extends beyond this particular event. Short gamma-ray bursts are difficult to detect when their beam is not directed toward Earth. A longer X-ray emission could be visible in more configurations and offer another way to identify certain compact-object mergers.
These collisions also interest gravitational-wave observatories. A simultaneous detection of gravitational waves and a long X-ray flash would directly link the light signal to the type of objects involved. It would also help determine what remains immediately after the merger.
Future telescopes capable of rapidly monitoring large portions of the sky in X-rays will be able to search for other similar events. Their number, duration, and association with gamma-ray bursts or gravitational waves will help determine whether these flashes truly constitute a frequent signature of newborn magnetars.