Discovery of Two Companion Stars Offers New Clues as to How Binary Systems Form

With the help of a newly-upgraded Karl G. Jansky Very Large Array (VLA), researchers have identified binary companions to a pair of infant protostars, offering support for one competing explanation for how double-star systems form.

Despite knowing that roughly half of all Sun-like stars are part of double or multiple-star systems, the debate over how they are formed is still alive and well.

"The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation," said John Tobin, of the National Radio Astronomy Observatory (NRAO). "That's what we've done with the stars we observed, and we got valuable new clues from them."

The new clues, presented in the Astrophysical Journal, suggest that double-star systems are born when a disk of gas and dust moving around a young star fragments. As this happens, a new star is formed in orbit with the first.

Tobin, along with an international team of astronomers, examined the young stars located some 1,000 light years from Earth where they found two previously unknown companions located where disks would be expected. One of the systems even had a clear disk surrounding both young stars.

"This fits the theoretical model of companions forming from fragmentation in the disk," Tobin said. "This configuration would not be required by alternative explanations."

The study adds support to observations carried out in 2006 when a VLA team discovered an orbiting pair of young stars - both surrounded by a disk of material aligned with each other in the same plane. Last year, Tobin and his colleagues discovered a large circumstellar disk forming around a protostar in its beginning stages of star formation.

"Our new findings, combined with the earlier data, make disk fragmentation the strongest explanation for how close multiple star systems are formed," said Leslie Looney of NRAO and the University of Illinois.