![]() In the first stage of this process, the more massive star of the pair begins to run out of fuel, transferring its outer layers to its less massive companion - which is destined to become the magnetar - causing it to rotate more and more quickly. This discovery allowed the astronomers to reconstruct the stellar life story that permitted the magnetar to form, in place of the expected black hole. “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,” adds Ben Ritchie (Open University), a co-author on the new paper. View full size.Wide-field view of the sky around the star cluster Westerlund 1 One star, known as Westerlund 1-5, was found to be doing just that. They hunted for runaway stars - objects escaping the cluster at high velocities - that might have been kicked out of orbit by the supernova explosion that formed the magnetar. But, up to now, no companion star was detected at the location of the magnetar in Westerlund 1, so astronomers used the VLT to search for it in other parts of the cluster. They suggested that the 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 Sun. We did not understand how it could have become a magnetar,” says Simon Clark, lead author of the paper reporting these results.Īstronomers proposed a solution to this mystery. ![]() ![]() But this presents its own problem, since stars this massive are expected to collapse to form black holes after their deaths, not neutron stars. “In our earlier work (eso1034) we showed that the magnetar in the cluster Westerlund 1 (eso0510) must have been born in the explosive death of a star about 40 times as massive as the Sun. It is called CXOU J164710.2-455216 and it has greatly puzzled astronomers. The Westerlund 1 star cluster, located 16 000 light-years away in the southern constellation of Ara (the Altar), hosts one of the two dozen magnetars known in the Milky Way. Magnetar surfaces release vast quantities of gamma rays when they undergo a sudden adjustment known as a starquake as a result of the huge stresses in their crusts. Like all of these strange objects they are tiny and extraordinarily dense - a teaspoon of neutron star material would have a mass of about a billion tonnes - but they also have extremely powerful magnetic fields. Magnetars are an unusual and very exotic form of neutron star. When a massive star collapses under its own gravity during a supernova explosion it forms either a neutron star or black hole. This discovery helps to explain how magnetars form - a conundrum dating back 35 years - and why this particular star didn’t collapse into a black hole as astronomers would expect. Artist’s impression of the magnetar in the star cluster Westerlund 1.Ī team of European astronomers using ESO’s Very Large Telescope (VLT) now believe they’ve found the partner star of a magnetar for the first time.
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