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Some stars have split personalities

USING THE NEW CAPABILITIES of the upgraded Karl G. Jansky Very Large Array (VLA) radio telescope system, scientists have discovered previously-unseen companions to a pair of very young protostars. The discovery gives strong support for one of the competing explanations for how double-star systems form.

Astronomers know that about half of all Sun-like stars are members of double or multiple-star systems, but have debated over how such systems are formed.

artist's impression shows a disc of dust and gas surrounding a star

This artist’s impression shows a disc of dust and gas surrounding a star that is still in the process of formation. Evidence suggests that such discs sometimes split, leading to the formation of two or more stars. Image courtesy ESO / L. Calçada.

“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,” he added.

Their new clues support the idea that double-star systems form when a flat cloud, called a disc, of gas and dust whirling around one young stars splits, forming another new star in orbit with the first. Astronomers call it the disc fragmentation model.

Fits the model

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 discs would be expected. One of the systems also clearly had a disc 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,” he added.

Aerial view of VLA dishes in a Y-shape

Dishes of the Karl G. Jansky Very Large Array. NRAO image.

The new observations add to a growing body of evidence supporting the disc-fragmentation idea. In 2006, a different VLA observing team found an orbiting pair of young stars, each of which was surrounded by a disc of material. The two discs, they found, were aligned with each other in the same plane. Last year, Tobin and his colleagues found a large disc forming around a protostar in the initial phases of formation. This showed that discs are present early in the star formation process, a necessity for binary pairs to form through disc fragmentation.

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

Adapted from information issued by NRAO.

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