Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the Universe — millions of times more powerful than the strongest magnets on Earth. A 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.
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.
What Is A Magnetar? When a massive star collapses under its own gravity during a supernova explosion it forms either a neutron star or black hole. Magnetars are an unusual and very exotic form of neutron star. 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. 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.
CXOU J164710.2-455216 Led by astronomer Simon Clark from the Open University, the team of researchers used the European Southern Observatory’s Very Large Telescope to observe CXOU J164710.2-455216, a magnetar located in the Westerlund 1 star cluster, a tight group of young massive stars, in the constellation Ara.
CXOU J164710.2-455216 is what was left following the supernova of a star with a mass 40 times that of the sun, says Clark. When a star reaches the end of its life and goes supernova, what’s left is a neutron star, an incredibly dense star, or a black hole.
According to Clark, the remnant of the supernova of such a massive star should have been a black hole, but that’s not the case with CXOU J164710.2-455216. The next step for scientists was to explain why a magnetar was formed and not a black hole, and they got an answer after discovering a “runaway” star in the Westerlund 1 cluster.
The star, Westerlund 1-5, was traveling at high speed, compared to other stars in the area, away from the cluster. The researchers believe Westerlund 1-5 was traveling so fast as a result of the supernova responsible for the magnetar.
They say Westerlund 1-5 began shedding its outer layers as it began to run out of the necessary fuel for nuclear fusion. This material was transferred to its companion star in the binary system, the star that became the magnetar, causing it to spin faster; the fast rotation is a key component responsible for the strong magnetic field.
As the star gains more mass it too begins to shed its outer layers before going supernova. The star lost enough mass to prevent it from becoming a black hole, which was the second important component necessary to form a magnetar.
Francisco Najarro, from the Centro de Astrobiologia in Spain, participated in the research and said in a statement, “It is this process of swapping material that has imparted the unique chemical signature to Westerlund 1-5 and allowed the mass of its companion to shrink to low enough levels that a magnetar was born instead of a black hole — a game of stellar pass-the-parcel with cosmic consequences!”
Zooming in Westerlund 1 In this video we fly through the young star cluster Westerlund 1 and close in on the strange magnetar that lies within it. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns.