Stellar neighbor could support Earth-like planet

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Turbulent binary star systems, such as our closest stellar neighbor, Alpha Centauri, could host Earth-sized planets, new computer modeling indicates.

Scientists have so far been unsure whether planets could form amid the chaotic gravitational tug-of-war between two binary stars. Some recent studies have suggested they could, but these projects have focused on modeling the final stage of planet formation. Now researchers have probed whether or not the necessary precursor to planet formation — a so-called "protoplanetary" disk of planet building blocks — could survive in this environment.

The answer appears to be yes, at least under certain conditions, such as a specific range of gas densities and star orientations. And in the specific case of Alpha Centauri B (CenB), one of two binary stars in the system Alpha Centauri, these conditions are right. The system is about 4.2 light-years away.

"It is quite possible that a habitable Earth-like planet may be hidden around CenB," the researchers, led by Jian Ge of the University of Florida in Gainesville, wrote in a paper recently submitted to the Astrophysical Journal.

The scientists built a computer model to test the birth of baby solar systems around binary stars. They were able to alter starting conditions such as the arrangement of the parent stars, and the amount of gas in the system. They then ran their simulations over a multitude of conditions to discover which factors would lead to a disk of planetary embryos forming between 0.5 to 2.5 times the distance between the Earth and the sun — roughly the zone in which a terrestrial planet might be habitable.

The researchers also tested the case of Alpha Centauri B.

This star is just a bit smaller than our own sun, at about 0.93 times the sun's mass. Its partner, Alpha Centauri A, weighs about 1.1 times the sun's mass. They are the closest stars to the sun after their smaller companion Proxima Centauri.

Although no extrasolar planets have yet been discovered around any of these stars, Alpha Centauri B in particular is thought to be a prime candidate for hosting an Earth-like planet in or near its habitable zone.

The results are "encouraging" for the case of Alpha Centauri B, the scientists said.

"Although planetesimal accretion in CenB is significantly less efficient and slowed-down as compared to single star systems, it is still possible," they wrote.