Astronomers Discover How Exotic Magnetar is Born: Two Massive Stars Interact

Astronomers may have discovered just how magnetars form. These exotic forms of neutrons stars may just form through the interactions of two massive stars.

Magnetars are relatively small and extraordinarily dense. In fact, a mere teaspoon of material from these stars would have a mass of about a billion tons. What makes them more unusual, though, are their strong magnetic fields. Magnetars also have the potential of releasing vast amounts of gamma rays when they undergo a sudden adjustment known as a starquake as a result to huge stresses in their crust. Yet scientists have long wondered exactly how they form.

"In our earlier work, we showed that the magnetar in the cluster Westerlund 1 must have been born in the explosive death of a star about 40 times as massive as the sun," said Simon Clark, one of the researchers, in a news release. "But this presents its own problem, since stars this massive are expected to collapse to form black holes after their deaths, not neutron stars. We did not understand how it could have become a magnetar."

In order to get a better sense of how this particular magnetar formed, the researchers looked at a magnetar called CXOU J164710.2-455216. Located in the Westerlund 1 star cluster, it's about 16,000 light-years away from Earth in the southern constellation of Ara.

"Not only does this star have the high velocity expected if it is recoiling from a supernova explosion, but the combination of its low mass, high luminosity and carbon-rich composition appear impossible to replicate in a single star--a smoking gun that shows it must have originally formed with a binary companion," said Ben Ritchie, one of the researchers, in a news release.

It's very likely that this magnetar formed through the interactions of two very massive stars orbiting one another in a binary system so compact that it would fit within the orbit of the Earth around the star. Yet until now, no companion star was detected at the location of the magnetar. Using the Very Large Telescope (VLT), though, the researchers managed to hunt down a star, now called Westerlund 1-5.

The findings reveal a little more about magnetars, and show how this particular one formed. This, in turn, allows astronomers to learn a little bit more about these strange bodies in our universe.

The findings are published in the journal Astronomy and Astrophysics.