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Young stellar system caught in act of forming close multiples

Staff Writer |
For the first time, astronomers have seen a dusty disk of material around a young star fragmenting into a multiple-star system.

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Scientists had suspected such a process, caused by gravitational instability, was at work, but new observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA) revealed the process in action.

"This new work directly supports the conclusion that there are two mechanisms that produce multiple star systems - fragmentation of circumstellar disks, such as we see here, and fragmentation of the larger cloud of gas and dust from which young stars are formed," said John Tobin, of the University of Oklahoma and Leiden Observatory in the Netherlands.

Stars form in giant clouds of gas and dust, when the tenuous material in the clouds collapses gravitationally into denser cores that begin to draw additional material inward. The infalling material forms a rotating disk around the young star.

Eventually, the young star gathers enough mass to create the temperatures and pressures at its center that will trigger thermonuclear reactions.

Previous studies had indicated that multiple star systems tend to have companion stars either relatively close, within about 500 times the Earth-Sun distance, or significantly farther apart, more than 1,000 times that distance.

Astronomers concluded that the differences in distance result from different formation mechanisms. The more widely-separated systems, they said, are formed when the larger cloud fragments through turbulence, and recent observations have supported that idea.

The closer systems were thought to result from fragmentation of the smaller disk surrounding a young protostar, but that conclusion was based principally on the relative proximity of the companion stars.


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