Magnetars are among the most fascinating astronomical objects. A teaspoon of the material they’re made of would weigh nearly a billion tons, and they have magnetic fields hundreds of millions of times stronger than any magnetic field existing on Earth today. But we don’t know much about how they form. A new paper points to a possible source – neutron star mergers.
Neutron stars themselves are just as fascinating in their own right. In fact, magnetars are generally thought of as a specific form of neutron star, with the main difference being the strength of that magnetic field. There are thought to be about a billion neutron stars in the Milky Way, and some of them happen to occur in binary pairs.
When gravitationally bound together, the stars enter a final dance of death, usually resulting in either a black hole or possibly one or both turning into a magnetar. This 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 happen, it’s spectacular, and a team of researchers think they discovered that this happened just weeks before it was discovered.
More specifically, it happened about 228 million years ago, that’s how far away is the galaxy where it happened. However, light from this spectacular event reached sensors at Pan-STARRs just a few weeks before it began observing this patch of sky. And what sets this magnetar apart from all others that scientists have found is its spinning speed.
Typically, neutron stars rotate thousands of times per minute, making their period on the order of milliseconds. But the magnetars scientists have found differ in that their rotation time is much slower, typically only once every two to ten seconds. But GRB130310A, as the new magnetar is now called, has a rotation period of 80 milliseconds, putting it closer to neutron star magnitude 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 spin deceleration, as has happened to many other observed magnetars. But the fact that its rotation period is approaching the rate of neutron stars points to its potential starting point as one of those neutron stars themselves.
This rotation slowdown that GRB130310A is currently undergoing will last for thousands of years, but eventually magnetars will fade and become almost undetectable. An estimated 30 million dead magnetars are floating around the Milky Way, and at least some of these likely began with the same dramatic orbital periods as GRB130310A.
Another indication that the new magnetar was formed from a neutron star merger was the lack of precursor events that observatories may have picked up. There was no supernova and no gamma-ray burst, both of which usually precede the birth of a magnetar. So it appears that researchers have stumbled upon a neutron star merger, which they spotted almost exactly as it happened.
There are other ways to detect neutron star mergers, such as through the gravitational waves they sometimes emit. It’s unclear whether other instruments were able to detect this merger to confirm that the event happened as the researchers suspect. But if so, it’s another data point that confirms the longstanding idea that magnetars, at least sometimes, form from neutron star mergers. And many more observations of similar events across the universe will become available to confirm or disprove this theory.