14 May 2014

OU helps unlock mystery of supernova explosions and black holes

Supernova explosion and black holes

Supernova explosion and black holes

OU researchers are part of an international team which has just discovered how magnetars – remnants of supernova explosions - form, and why they did not collapse into a black hole.

In a paper published today (14 May) in the journal Astronomy and Astrophysics the researchers describe how by using European Southern Observatory’s (ESO) Very Large Telescope (VLT), they believe they have found the partner star of a magnetar for the first time. This discovery helps solve a conundrum dating back 35 years – specifically how magnetars form and why this particular star didn’t collapse into a black hole as astronomers would expect.

The paper explains that 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.

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. Its full name is CXOU J164710.2-455216 and it has greatly puzzled astronomers.
Simon Clark, from The Open University’s Faculty of Science, is lead author of the paper reporting the results. He said: “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. 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.”

The team that worked on this research is composed of Simon Clark and Ben Ritchie (The Open University, UK), Francisco Najarro (Centro de Astrobiología, Spain), Norbert Langer (Universität Bonn, Germany, and Universiteit Utrecht, the Netherlands) and Ignacio Negueruela (Universidad de Alicante, Spain).The same team published a first study of this object in 2006 (“A Neutron Star with a Massive Progenitor in Westerlund 1” by M. P. Muno et al., Astrophysical Journal, 636, L41).


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