Magnetar Formation- Mystery Solved

Artist's impression of magnetar. Credit: ESO/L. Calçada

Magnetars are the super-dense leftovers of supernova detonations. Magnetars are the strongest magnets so far identified in the Universe. Magnetars are actually millions of times more powerful than any of the strongest magnets on the Planet Earth. Recently a team of astrophysicists using ESO's Very Large Telescope now consider that they've discovered the companion star of a magnetar for the first time. This recent finding helps to clarify how magnetars form and why this specific star didn't collapse into a black hole as astrophysicists would assume.

The Westerlund 1 star cluster is positioned 16 000 light-years away in the southern constellation of Ara and contains one of the two dozen magnetars so far discovered in the Milky Way Galaxy. It is entitled as CXOU J164710.2-455216 and it has seriously confused astronomers.

When a massive star collapses due to its own gravity through a supernova detonation it forms one or the other a black hole or a neutron star and Magnetars are rare and very unusual kind of neutron star. Like neutron stars they are tiny and extremely dense but they also produce enormously powerful magnetic fields. Magnetar surfaces also release huge quantities of gamma rays.

Astrophysicists suggested an explanation to this mystery. They proposed that the magnetar made by the connections of two very gigantic stars circling one another in a binary system so dense that it would fit inside the orbit of the Earth around the Sun. But, until now, no partner star was discovered at the position of the magnetar in Westerlund 1, so astrophysicists used the VLT to hunt for it in other regions of the cluster. They searched for escaped stars (objects dodging the cluster at high velocities) that might have been hit out out of orbit by the supernova detonation that made the magnetar. One star, identified as Westerlund 1-5, was discovered to be doing just that.

Ben Ritchie (Open University), a co-author on the new paper says “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,”

This finding allowed the stargazers to rebuild the stellar life story that allowed the magnetar to form, instead of the predicted black hole. In the initial phase of this procedure, the more massive star of the pair initiates to run out of its fuel, relocating its external layers to its less massive partner star, which is meant to turn into the magnetar, initiating it to revolve more and more rapidly. This rapid spin seems to be the vital component in the creation of the magnetar's ultra-strong magnetic field.

In the next phase, as an outcome of this mass transmission, the partner itself becomes so gigantic that it in turn sheds a huge amount of its newly extended mass. Considerable amount of this mass is lost but some is handed back to the original star that we still see shining currently as Westerlund 1-5. It appears that being a partner of a binary star might therefore be a vital component in the procedure for making a magnetar.

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