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). http://dx.doi.org/10.1038/nature20600
