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Scientists discover new “anti-glitch” in neutron stars

by CIFAR Jun 3 / 13

A neutron star is an exotic type of star that is created when a dying star collapses on itself. A so-called magnetar is a type of neutron star that has an extremely high magnetic field, the highest known in the Universe. Scientists estimate that there may be hundreds of active magnetars in our solar system. It is unknown how many there are in the Universe because they are very faint.

E7_Magnetar
The magnetar 1E 2259+586 shines a brilliant blue-white in this false-color X-ray image.
Credit: ESA/XMM-Newton/M. Sasaki et al.

Magnetars have been observed to have quirky behaviour and occasionally speed up, which scientists have termed a “glitch” because they initially believed that there was something wrong with their own equipment when this phenomenon was first discovered.

Just a year ago, one of the magnetars that Senior Fellow Vicky Kaspi (McGill) had been observing for the last seventeen-and-a-half years, named 1E 2259+586, did something completely different. It slowed down.

“We think these stars are filled with a kind of ‘super fluid’ made of neutrons,” explains Kaspi, “that is spinning faster than the crust of the star. Every now and again, the inside fluid of the star will give some kind of added momentum and will spin the crust up a tiny bit. In scientific terms, that is called a ‘glitch.’ But just a year ago, one of the magnetars we were observing very suddenly slowed down, and neutron stars don’t usually slow down so suddenly. It’s a phenomenon that’s never been confirmed before, and it’s telling us that something unusual is probably going on in the centre of the magnetars. It’s very exciting.”

At one point, Kaspi had given thought to dropping the observation of the magnetar, but she read a scientific paper that suggested it was theoretically possible for a magnetar to have an x-ray explosion. And in 2002, the magnetar she was observing, 1E 2259+586, had one.

“It was one of those eureka moments,” says Kaspi, “a puzzle you’ve been thinking about for years, and then suddenly you have an answer.”

The team continued to monitor the star for the next decade, about an hour and a half every few weeks, when in 2012, the magnetar was observed to slow down suddenly, a behaviour Kaspi has termed to be an “anti-glitch.”

“This is exciting because it challenges models for the physics of neutron star interiors,” says Kaspi. “I’ve already been in touch with some theorists who are trying to explain the mechanism behind it.”

She will continue to monitor this magnetar and six other celestial objects to see what else the Universe might reveal.

The results of this study are published in Nature.

This work was funded by the Natural Sciences and Engineering Research Council of Canada Discovery Grant, The Canadian Institute for Advanced Research, Fonds de Recherche Nature et Technologies Quebec, from the Canada Research Chairs and the Lorne Trottier Chair in Astrophysics and Cosmology.