New evidence explains the formation of binary star systems

The discovery of two previously-unseen binary companions to two young protostars has given strong support the theory that binary and multiple-star systems form from a fragmented formation disk.

Researchers at the National Radio Astronomy Observatory observed the two protostars, still in the process of formation, using the upgraded Karl G. Jansky Very Large Array (VLA), and discovered their companions.

Binary systems appear to be formed when a disk of gas and dust surrounding a young star breaks away and forms another star in the orbit of the first. Young stars still gathering material tend to form such disks and often produce jet-like propulsions of material perpendicular to the disk.

"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 NRAO. "That's what we've done with the stars we observed, and we got valuable new clues from them."

Scientists believe around half of all Sun-like stars are part of a double- or multiple-star system. When they studied young stars around 1,000 light years away, they found these previously unseen companions in the plane where the disks were expected to be seen.

The findings support evidence found by a different NRAO team studying a pair of young stars, each surrounded by a disk aligned in the same plane. And last year, Tobin and his colleagues found a large disk forming around a protostar in the initial stages of star formation, suggesting that disk formation in the initial phases of star formation are a necessity for binary star systems.

"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.

[NRAO]