Do brown dwarfs share stars' formation process?

An analysis of a patch of still-forming brown dwarfs shows they may propel jets outward from a surrounding disc in much the same way as young forming stars.

Artist's conception of a brown dwarf in its formation stage, with a disc of material orbiting it and jets ejecting from its poles.
Credit: Bill Saxton, NRAO/AUI/NSF

Brown dwarfs could form by the same process as stars, a new study has suggested.

Astronomers studying a sample of brown dwarfs still in their formation stage have found that four are expelling the same kind of jets emitted by stars during their formation.

Brown dwarfs are smaller than massive stars, but bigger than giant planets. Still, they have insufficient mass to produce temperatures and pressures needed to trigger the thermonuclear reactions that power normal stars.

Scientists are still trying to confirm whether brown dwarfs form like stars or like planets. This latest discovery shows that the former could be the case, because stars form when a cloud of gas and dust in interstellar space collapses through gravity and begins accumulating mass.

A disc material begins orbiting around the star and, eventually, planets form within the disc, creating a planetary system. Early on in this process, jets of material spurt outward from the poles of the disc. This does not occur in planet formation, however.

"We conclude that the formation of brown dwarfs is a scaled-down version of the process that forms larger stars," says Oscar Morata of the Institute of Astronomy and Astrophysics of the Academia Sinica in Taiwan, who led the study. "This is the first time that such jets have been found coming from brown dwarfs at such an early stage of their formation, and shows that they form in a way similar to that of stars. These are the lowest-mass objects that seem to form the same way as stars.”

The study was made using the Karl G. Jansky Very Large Array (VLA) to focus on a sample of brown dwarfs that are still forming in a region in the constellation Taurus.


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