Lee Rannals for redOrbit.com – Your Universe Online
Scientists have reported in the journal Nature that they have figured out by using computer simulations how wide binary stars are able to form.
Wide binary stars are two stars that orbit each other at a distance up to a light year. Some binary stars can be very close, while other pairs are extremely far apart.
Astronomers have known about wide binary pairs for a long time, but how they form has remained a mystery. Now, astronomers from University of Hawaii and University of Turku, Finland have used computer simulations to unravel the mystery.
When more than two stars are together in a small space, they gravitationally pull on each other in a dance, where the lightest body is often kicked out to the outskirts of the core for long periods of time before falling back into the mix-up.
The remaining stars begins to feed on the gas at the center of the cloud core and grow. Eventually, the runt of the group gets such a large kick that it may be completely ejected. In some cases, the kick is not strong enough for a third body to fully escape, so it is sent into a very wide orbit.
The implication is that the widest binaries should be three stars, not just two. When astronomers inspect the stars in a very wide system, they find that one of them is a tight binary. Sometimes, it appears that there really are two stars in a wide system. This means either wide binaries with only two stars are formed in another way, or something has happened to one of the stars that was once a close binary.
The researchers say that stars in a close binary merged into a single, larger star. As the two stars in close binary move around each other, they lose energy and spiral toward each other. Sometimes there is so much gas in the core that the two close stars spiral all the way in and collide with each other in a merging explosion.
Alpha Centauri is the closet wide binary to Earth. The system is actually a close binary, but it also has a small distant companion called Proxima Centauri that is about 15,000 times the Earth-Sun distance, or a quarter of a light-year.
Several billions of years ago, all three stars were born close together, before a violent event sent Proxima out into its wide orbit, where it has been moving since.