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Monday, January 16, 2017

Newly Formed Stars Shoot Out Powerful Whirlwinds

Astronomers led by Per Bjerkeli, Chalmers, have used the telescope Alma to observe the early stages in the formation of a new solar system. For the first time they have seen how a powerful whirlwind is launched from a rotating disk surrounding the young star. The results are published on 15 December 2016 in Nature.

A new solar system is formed in a large cloud of gas and dust that contracts and condenses due to the force of gravity. Eventually it becomes so compact that the centre collapses into a ball of gas where the pressure heats the material, resulting in a glowing globe of gas: a star. The remains of the gas and dust cloud rotate around the newly formed star in a disc. The material in the disc starts to accumulate and form larger and larger clumps, which finally become planets.

​Artist’s impression of the wind from the young solar system TMC1A. The rotating wind is formed in the disc surrounding the protostar.​​
Credit: ​D. Lamm/BOID and P. Bjerkeli/Chalmers

Close to newly formed stars, called protostars, scientists have observed evidence powerful whirling winds and outflows. But before now, no one had observed how these winds are formed.

“Using Alma, we have observed a protostar at a very early stage. We see how the wind, like a tornado, lifts material and gas up from the rotating disc, which is in the process of forming a new solar system,” explains Per Bjerkeli, astronomer at Chalmers and the Niels Bohr Institute at the University of Copenhagen, Denmark.

In this clip, we see the surroundings of a star which has recently been formed from a large cloud of gas and dust that contracts due to the force of gravity. New observations with ALMA have shown how the new star emits a powerful wind, which carries away energy and slows down the rotation. Since the wind is formed in the disc around the protostar, it rotates together with the disc. Like a tornado, it lifts material up from the gas and dust cloud and at some point the wind releases its hold on the cloud, so that the material floats freely. This has the effect that the rotation speed of the cloud is slowed and thus the new star can hold together and grow.
Newly formed star shoots out powerful whirlwind from Chalmers Univ. of Technology on Vimeo.

Credit: D. Lamm/BOID and P. Bjerkeli/Chalmers

Slowed down by a tornado

The telescope Alma (Atacama Large Millimeter/submillimeter Array) consists of 66 antennas which observe the universe in light with wavelength around one millimetre from the Chajnantor plateau at 5000 metres altitude in northern Chile. The observed protostar, called TMC1A, is located in the constellation Taurus (the Bull), 450 light years away. The researchers have now observed details never seen before in a system of this kind.

“During the contraction of the gas cloud, the material begins to rotate faster and faster just like a figure skater doing a pirouette spins faster by pulling their arms close to their body. In order to slow down the rotation, the energy must be carried away. This happens when the new star emits a wind. The wind is formed in the disc around the protostar and thus rotates together with it. In this way, when this rotating wind moves away from the protostar, it takes part of the rotational energy with it and the dust and gas close to the star can continue to contract,” explains Per Bjerkeli.

How is this wind created? Up to now scientists have thought that it could originate from inside the centre of the rotating disc of gas and dust, but the new observations argue for a different origin for the wind.

ALMA’s observations of TMC1A reveal gas motions close to a protostar. Here blue colour indicates gas that is moving towards us while the red colour indicates gas moving away from us. The protoplanetary disc is shown in green. The grey spirals indicate the boundaries of the swirling outflow from the star. The observations, of emission from carbon monoxide molecules, were made with ALMA at 1.3 mm wavelength.
Credit: Onsala rymdobservatorium

“We can see that the rotating wind formed across the entire disc. Like a tornado, it lifts material up from the cloud of gas and dust. At some point the wind releases its hold on the cloud, so that the material floats freely. This has the effect that the rotation speed of the cloud is slowed and thus the new star can hold together. In the process, the material in the rotating disc of gas and dust accumulates and forms planets,” explains Jes Jørgensen, also at the Niels Bohr Institute and the Centre for Star and Planet Formation at the University of Copenhagen.
Future observations with Alma and other telescopes will tell us more about how planetary systems form around protostars like this one, explains Matthijs van der Wiel, astronomer at Astron, Netherlands.

“The next thing we want to find out is whether the material released from the disc is completely blown away or whether it falls back onto the disc at some point and becomes part of the planet-forming system”, he says.



Contacts and sources:
Per Bjerkeli, Department of Earth and Space Science, Chalmers University of Technology and Niels Bohr Institute, University of Copenhagen,

Citation:  Robert Cumming, communicator, Onsala Space Observatory, Chalmers University ofThe research is published in a paper, “Resolved images of a protostellar outflow driven by an extended disk wind”, by P. Bjerkeli et al., in the 15 December 2016 issue of the journal Nature, http://www.nature.com/nature/journal/v540/n7633/full/nature20600.html



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