Saturday, January 07, 2017

Newly formed stars shooting out strong whirlwinds

Newly formed stars shooting out strong whirlwinds

Researchers from, among others, ASTRON and the Niels Bohr Institute in Denmark have used the ALMA-telescope in order to observe the earliest stages in the formation of a new solar system. For the first time, they observed how strong "whirlwinds" shooting from the rotating cloud of gas and dust. The results will be presented on 15 December in the scientific journal Nature.

A new solar system is formed in a large cloud of gas and dust, which contracts as a result of the force of gravity and becomes denser. This ultimately produces a hot gaseous sphere in the middle, a star. Surrounding the star forms a disk in which the material gradually clumps together and eventually planets are formed.

It has long been known that newly formed stars, called protostars, are accompanied by whirlwinds and jets. But until now no one observed how these winds form.

"With the ALMA-telescopes we have observed a protostar in a very early phase. We see how the wind lifts material and gas from the rotating disk like a tornado, which is in the process of forming a new solar system." Explains Per Bjerkeli, post doc in Astrophysics and Planet-research of the Niels Bohr Institute at University of Copenhagen as well as Chalmers Technical University in Sweden.

The ALMA-observatory (Atacama Large Millimeter/submillimeter Array) consists of 66 telescopes, that together observe as if they were a single mirror with a diameter of 16 kilometers. The observed protostar is located 450 light years away. The enormous size of ALMA has made it possible for researchers to capture details that had never been seen before.

Slowing down

"Under the contraction of the gas cloud, material starts rotating faster and faster in the same way an ice skater can rotate faster by pulling the arms in toward the body. To slow this rotation the energy needs to be carried away. That is done by the wind ejected by the new star. The wind is formed in the disk and rotates together with it. When the rotating wind moves further away from the protostar it brings part of the rotation energy with it so that the protostar can continue collapsing", explains Per Bjerkeli.

Previously, it has been suggested that the rotating wind arose in the middle of the rotating gas and dust disk, but the new observations show something different.

"We can see that the rotating wind is spewed out from the entire disk, instead of from a small area very close to the young star. As in a tornado, the material is being lifted from the disk, and at some point the wind leaves the cloud. As a result, the rotation in the disk slows down and material gets a chance to form new planets, "explains Jes Jørgensen, associate professor at the University of Copenhagen.

"Future observations with ALMA and other telescopes will tell us more about the formation of galaxies around these and other protostars," explains Matthijs van der Wiel, 'telescope scientist' at ASTRON. "The next question for us is whether the regurgitated material is completely blown away by the wind, or that part of it can fall back on the disk and re-enters the planet-forming system."

Article: P. Bjerkeli, M.H.D. van der Wiel, D. Harsono, J.P. Ramsey, J.K. Jørgensen. Resolved images of a protostellar outflow driven by an extended disk wind. Nature 540, 406-409 (2016).