NASA's Chandra X-ray Observatory caught the stellar switch-a-roo inside a cluster of stars named Westerlund 1. The arrow points to the neutron star.
Credit: NASA
PARIS: A neutron star with a mighty magnetic field has thrown down the gauntlet to theories about stellar evolution and the birth of black holes.
The 'magnetar' lies in a cluster of stars known as Westerlund 1, located 16,000 light years away in the constellation of Ara, the Altar.
Westerlund 1, discovered in 1961 by a Swedish astronomer, is a favoured observation site in stellar physics.
Cluster of superstars
It is one of the biggest clusters of superstars in the Milky Way, comprising hundreds of very massive stars, some shining with a brilliance of almost a million Suns and some two thousand times the Sun's diameter.
The cluster is also, by the standards of the Universe, very young. The stars were all born from a single event just three and a half to five million years ago.
Within Westerlund 1 is the remains of one of galaxy's few magnetars -- a particular kind of neutron star, formed from the explosion of a supernova, that can exert a magnetic field a million, billion times strong than Earth's.
40 times the mass of the Sun
The Westerlund star, which eventually became the magnetar, must have been at least 40 times the mass of the Sun, according to the study, which appears in the research journal Astronomy and Astrophysics.
If so, intriguing questions are raised.
The mainstream assumption is that stars of between 10 and 25 solar masses go on to form neutron stars. But those above 25 solar masses produce black holes - the light-gobbling gravitational monsters that are formed when a massive, dying star collapses in on itself.
But no black hole
In that case, the magnetar's mother should have become a black hole because it was so big.
But another alternative, say the authors, is that the star 'slimmed' to a lower mass, enabling it to become a neutron star. How did this happen?
