Why Most Stars Have Twins : Discovery News

New observations help explain why "only child" suns like are own are the exception in a galaxy packed with solar twins.


Most of the stars in the galaxy are not singles, like our sun, but twin or triplets.

Clouds of gas and dust that give rise to baby stars are elongated, not round as theorized.

This makes twin and multiple star systems easier to explain.

Most of the stars twinkling in the night sky aren't alone. They're pairs, triplets or other groups, and scientists haven't understood why.

New research suggests that asymmetries in the dust-laced clouds of gas that feed baby stars are responsible.

"There's always been a big confusion about why there are so many binaries," said astronomer Leslie Looney, with the University of Illinois Urbana-Champaign. "We think it has to do with when a cloud of material collapses down and forms these asymmetrical blobs."

Scientists used NASA's Spitzer Space Telescope to peer within dusty stellar wombs and noted clumps of material in most of the objects. They theorize that the blobs cause the star-forming clouds to elongate into something shaped like dumbbells, which then break apart, forming twin stars.

"The prevailing theories are based on clouds that are very spherical. What we've seen is that the clouds themselves are, in general, not close to being round at all. They're very lumpy," said astronomer Lee Hartmann, with the University of Michigan.

Given the prevalence for elongated, rather than round, star-forming clouds, the research raises new questions about why some stars, like our own sun, are single.

Hartmann suspects that whether a star-forming cloud produces a single or multiple star depends on how fast it spins, as well as its size. Slow-spinners may stay more spherical, generating a single star.

On the other hand, spin rates may be so fast that sibling stars formed together are catapulted away from each other, drifting over time so that they appear as single stars today.

Follow-up studies are under way to gather more information about how fast the star-forming clouds spin, as well as to pinpoint trace chemicals that should provide information about the clouds' densities.

The study is based on infrared observations of 20 precursor stars that are between 1 million and 10 million years away from having their cores ignite with nuclear fusion.

University of Michigan scientists were studying how jets and other outflows impacted clouds of dust around young stars when they noticed the asymmetries. Further analysis revealed that 17 of the 20 clouds were irregularly shaped, rather than spherical. The remaining three weren't perfectly round either.

The research is published in The Astrophysical Journal.