You wait ages for a sun, then two come along at once: All stars have twins, say astroboffins

So where is our Sol's sibling?

Nearly all stars, including our Sun, are born from hot, dense molecular clouds and come in pairs, according to a paper to be published in the Monthly Notices of the Royal Astronomical Society.

Binary star systems are common in space. It was estimated that up to 80 per cent of massive, bright O‑type and B‑type stars are locked in multiple star systems, and that around 50 per cent of sun-like stars have companions.

Steven Stahler and Sarah Sadavoy, research astronomers from the University of California, Berkeley and the Smithsonian Astrophysical Center, now estimate that percentage to be closer to 100.

“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries,” said Stahler, co-author of the paper.

It means that stars like our Sun were born with a twin – often nicknamed Nemesis – but after about a million years, it either shrank or drifted away. “We are saying, yes, there probably was a Nemesis, a long time ago,” he added.

A wide binary means that twin stars are separated by more than 500 astronomical units – 500 times the distance between the Sun and Earth (93 million miles). The large distance means that the gravitational pull between stars like the Sun and Nemesis weakened, allowing Nemesis to escape and blend into a crowd of background stars in the Milky Way.

It makes finding direct evidence of their theory difficult. Astronomers have found that a greater proportion of younger stars are found in binary systems, but explaining why remains a problem in astrophysics.

“The idea that many stars form with a companion has been suggested before, but the question is: how many?” said Sarah Sadavoy, first author of the paper.

“The key here is that no one looked before in a systematic way at the relation of real young stars to the clouds that spawn them. Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution. We now believe that most stars, which are quite similar to our own sun, form as binaries. I think we have the strongest evidence to date for such an assertion,” she explained.

The next stage will be to run similar simulations with different molecular clouds and check the results against the Perseus cloud to see if their model is correct. The Perseus molecular cloud is a nearby giant stellar nursery – measuring 50 light years long – which is 600 light years away from Earth.

The paper is available now on arXiv. ®


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