Tuorla Observatory News 14 December 2012

Computer simulations about the formation of wide binary stars

The formation of very wide binary systems, such as the a Centauri system with Proxima (also known as a Centauri C) separated from a Centauri (which itself is a close binary A/B) by 15,000 astronomical units (1 AU is the distance fromEarth to the Sun), challenges current theories of star formation, because their separation can exceed the typical size of a collapsing cloud core. Various hypotheses have been proposed to overcome this problem, including the suggestion that ultrawide binaries result from the dissolution of a star cluster when a cluster star gravitationally captures another, distant, cluster star. Recent observations have shown that very wide binaries are frequently members of triple systems and that close binaries often have a distant third companion. The authors run N-body simulations of the dynamical evolution of newborn triple systems still embedded in their nascent cloud cores that match observations of very wide systems. The result is that although the triple systems are born very compact and therefore initially are more protected against disruption by passing stars, they can develop extreme hierarchical architectures on timescales of millions of years as one component is dynamically scattered into a very distant orbit. The energy of ejection comes from shrinking the orbits of the other two stars, often making them look from a distance like a single star. Such loosely bound triple systems will therefore appear to be very wide binaries.

Read more information about the results in the Nature letter: doi:10.1038/nature11662

This page was last modified by  Pasi Nurmi  on  12/21/2012  astroweb@utu.fi