Astronomers have used the Atacama Large Millimeter/submillimetre Array (ALMA) to observe the early stages in the formation of a new star system. For the first time, they have seen how a powerful whirlwind shoot out from the protoplanetary disk surrounding a newborn star (a so-called protostar).
This is an artist impression of the whirlwind being lifted up from the protoplanetary disk around the 100,000-year-old protostar TMC1A. Image credit: Per Bjerkeli / David Lamm / BOID.
A new solar system is formed in a large cloud of gas and dust that contracts and condenses due to the force of gravity and eventually becomes so compact that the center 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 protostar in disk where the material starts to accumulate and form larger and larger clumps, which finally become planets.
In connection with the protostars, astronomers have observed powerful emanations of whirlwinds and outflows, so-called jets. But before now, no one had observed how these winds are formed.
“Using ALMA, we have observed a protostar at a very early stage,” said Dr. Per Bjerkeli, an astronomer at the Niels Bohr Institute at the University of Copenhagen and Chalmers University of Technology.
The observed protostar, TMC1A, is located in the Taurus Molecular Cloud, approximately 457 light-years from Earth.
The object has a mass of 0.5 solar masses and is moving away from the solar neighborhood at a speed of 6.4 km/s.
“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,” Dr. Bjerkeli said.
“In order slow down the rotation, the energy must be carried away. This happens when the new star emits wind. The wind is formed in the disk around the protostar and thus rotates together with it.”
“When this rotating wind moves away from the protostar, it thus takes part of the rotational energy with it and the dust and gas close to the star can continue to contract.”
Previously, astronomers thought that the rotating wind originated from inside the center of the rotating disk of gas and dust, but ALMA observations indicate otherwise.
“We can see that the rotating wind formed across the entire disk. 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,” said Dr. Jes Jørgensen, also from the Niels Bohr Institute at the University of Copenhagen.
“This has the effect that the rotation speed of the cloud is slowed and thus the new star can hold together and in the process the material in the rotating gas and dust disk accumulates and forms planets.”
The next thing the astronomers want to find out is whether the released material is completely blown away or whether it falls back onto the disk at some point and becomes part of the planet-forming system.
The team’s findings were published in the Dec. 15 issue of the journal Nature.
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Per Bjerkeli et al. 2016. Resolved images of a protostellar outflow driven by an extended disk wind. Nature 540, 406-409; doi: 10.1038/nature20600
