https://en.wikipedia.org/wiki/Binary_star#Formation
Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first. Young stars that still are gathering matter from their surroundings form such disks along with jetlike outflows that rapidly propel material in narrow beams perpendicular to the disk.
When Tobin and an international team of astronomers studied gas-enshrouded young stars roughly 1,000 light-years from Earth, they found that two had previously unseen companions in the plane where their disks would be expected, perpendicular to the direction of the outflows from the systems. One of the systems also clearly had a 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 new observations add to a growing body of evidence supporting the disk-fragmentation idea. In 2006, a different VLA observing team found an orbiting pair of young stars, each of which was surrounded by a disk of material. The two disks they found were aligned with each other in the same plane. Last year, Tobin and his colleagues found a large circumstellar disk forming around a protostar in the initial phases of star formation. This showed that disks are present early in the star formation process, a necessity for binary pairs to form through disk fragmentation.
http://www.astronomy.com/news/2014/01/new-studies-give-strong-boost-to-binary-star-formation-theory
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