Why do most stars never form alone?
it is believed that maybe up to 50 per cent of all stars are in binary systems, with many researchers even suggesting that an even higher percentage of stars are born as binaries.
the high percentage of binary stars is closely linked to the way stars form. it is well established that most stars form in clusters rather than in isolation. in the dense parts of clusters such stars could pair up, forming binary stars. another way that binaries can form is by the breaking up of discs around newly formed stars. these discs are a natural result of the starformation process due to the initial rotation of the interstellar cloud that collapses to form a star. a disc increases in mass as more material from the cloud falls onto it and can become unstable or, in other words, it becomes too heavy to be maintained and fragments, breaking up into stars.
if fragmentation happens quickly after the first star has formed then the two stars may end up having similar masses. if it happens later on, the result will be a binary with two stars with unequal masses. the formation of more multiple star systems – triples, quadruples and so on – is also possible, and quite common. the study of binaries is important as their
properties contain information about how stars form.
Dr Dimitris Stamatellos is a guild research fellow of Astrophysics at the Jeremiah Horrocks Institute, University of Central Lancs