The case builds on colliding neutron stars creating magnetars

The case builds on colliding neutron stars creating magnetars

Artistic rendering of a neutron star. Credit: ESO/L Calcada

Magnetars are some of the most fascinating astronomical objects. A teaspoon of the stuff from which they are made would weigh nearly a billion tons, and they have magnetic fields hundreds of millions of times more powerful than any magnetic field existing on Earth today. But we don’t know much about how they form. A new paper points to one possible source: neutron star mergers.

Neutron stars themselves are equally fascinating in their own right. In fact, magnetars are generally considered to be a specific form of neutron star, the main difference being that star’s strength. magnetic field† It is thought that there are about a billion neutron stars in the Milky Way, and some happen to occur in binary pairs.

When bound together by gravity, the stars enter a final dance of death, usually resulting in a black hole or, possibly, one or both transformations into a magnetar. That process can take hundreds of millions of years to build up to a certain point where the actual explosion (or collapse) occurs. But when it does, it’s spectacular, and a team of researchers thinks they found that happened just weeks before they saw it.

More precisely, it happened about 228 million years ago, which is how far away the galaxy it happened in is. However, the light from this spectacular event only reached Pan-STARR’s sensors a few weeks before it began observing that patch of sky. And what sets this magnetar apart from all the others scientists have found is how fast it spins.

Typically, neutron stars rotate thousands of times per minute, so their period is on the order of milliseconds. But the magnetars scientists have found are distinguished by the fact that their rotation time is much slower, usually only once every two to 10 seconds. But GRB130310A, as the new magnetar is now known, has a rotation period of 80 milliseconds, bringing it closer to the order of neutron stars than the typical magnetar.

This discrepancy is likely due to the remarkably young age at which Zhang Binbin and his colleagues found this magnetar. It has yet to complete its rotational deceleration, as many other observed magnetars had. But the fact that its rotation period is approaching the speed of neutron stars points to its potential starting point as one of those neutron stars itself.

That rotational deceleration that GRB130310A is currently undergoing lasts for thousands of years, but eventually magnetars fade and become nearly undetectable. There are an estimated 30 million dead magnetars floating around the Milky Way, and at least some of them probably started with the same dramatic orbits as GRB130310A.

Another hint that the new magnetar originated from a neutron star merger was the lack of precursor events that observatories would have picked up. There was no supernova, and no gamma ray burstboth of which typically precede the birth of a magnetic† So it looks like the researchers discovered a neutron star merger that they discovered almost exactly when it happened.

There are other ways to detect neutron star mergers, such as by the gravitational waves they sometimes emit. It’s unclear whether other instruments have been able to capture this merger to confirm that the event happened as the researchers hypothesize. But if it did, it’s another data point that confirms the long-standing idea that magnetars are at least sometimes born from neutron star mergers. And many more observations of similar events throughout the universe will be available to help confirm or disprove that theory.

Unusual neutron star spinning every 76 seconds discovered in star graveyard

More information:
B.-B. Zhang et al, A week-old magnetar hyperflare born from a fusion between binary neutron stars. arXiv:2205.07670v1 [astro-ph.HE]†

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