New theory points to 'zombie vortices' as key step in star formation

Aug 20, 2013 by Sarah Yang
This is an illustration of a brown dwarf, spotted by NASA's Spitzer Space Telescope, surrounded by a spinning protoplanetary disk. Credit: NASA/JPL-Caltech

(Phys.org) —A new theory by fluid dynamics experts at the University of California, Berkeley, shows how "zombie vortices" help lead to the birth of a new star.

Reporting today (Tuesday, Aug. 20) in the journal Physical Review Letters, a team led by computational physicist Philip Marcus shows how variations in gas density lead to instability, which then generates the whirlpool-like vortices needed for stars to form.

Astronomers accept that in the first steps of a 's birth, of gas collapse into clumps that, with the aid of , spin into one or more Frisbee-like disks where a protostar starts to form. But for the protostar to grow bigger, the spinning disk needs to lose some of its angular momentum so that the gas can slow down and spiral inward onto the protostar. Once the protostar gains enough mass, it can kick off .

"After this last step, a star is born," said Marcus, a professor in the Department of Mechanical Engineering.

What has been hazy is exactly how the cloud disk sheds its angular momentum so mass can feed into the protostar.

Destabilizing forces

The leading theory in astronomy relies on magnetic fields as the destabilizing force that slows down the disks. One problem in the theory has been that gas needs to be ionized, or charged with a , in order to interact with a . However, there are regions in a protoplanetary disk that are too cold for to occur.

"Current models show that because the gas in the disk is too cool to interact with magnetic fields, the disk is very stable," said Marcus. "Many regions are so stable that astronomers call them dead zones so it has been unclear how disk matter destabilizes and collapses onto the star."

The researchers said current models also fail to account for changes in a protoplanetary disk's based upon its height.

"This change in density creates the opening for violent instability," said study co-author Pedram Hassanzadeh, who did this work as a UC Berkeley Ph.D. student in mechanical engineering. When the researchers accounted for density change in their computer models, 3-D vortices emerged in the protoplanetary disk, and those vortices spawned more vortices, leading to the eventual disruption of the 's angular momentum.

"Because the vortices arise from these dead zones, and because new generations of giant vortices march across these dead zones, we affectionately refer to them as 'zombie vortices,'" said Marcus. "Zombie vortices destabilize the orbiting gas, which allows it to fall onto the and complete its formation."

The researchers note that changes in the vertical density of a liquid or gas occur throughout nature, from the oceans where water near the bottom is colder, saltier and denser than water near the surface to our atmosphere, where air is thinner at higher altitudes. These density changes often create instabilities that result in turbulence and vortices such as whirlpools, hurricanes and tornadoes. Jupiter's variable-density atmosphere hosts numerous vortices, including its famous Great Red Spot.

Connecting the steps in star formation

This new model has caught the attention of Marcus's colleagues at UC Berkeley, including Richard Klein, adjunct professor of astronomy and a theoretical astrophysicist at the Lawrence Livermore National Laboratory. Klein and fellow star formation expert Christopher McKee, UC Berkeley professor of physics and astronomy, were not part of the work described in Physical Review Letters, but are collaborating with Marcus to put the zombie vortices through more tests.

Klein and McKee have worked over the last decade to calculate the crucial first steps of star formation, which describes the collapse of giant gas clouds into Frisbee-like disks. They will collaborate with Marcus's team by providing them with their computed velocities, temperatures and densities of the disks that surround protostars. This collaboration will allow Marcus's team to study the formation and march of zombie vortices in a more realistic model of the disk.

"Other research teams have uncovered instabilities in protoplanetary disks, but part of the problem is that those instabilities required continual agitations," said Klein. "The nice thing about the zombie vortices is that they are self-replicating, so even if you start with just a few vortices, they can eventually cover the in the disk."

Explore further: Smallest known galaxy with a supermassive black hole found

More information: Three-Dimensional Vortices Generated by Self-Replication in Stably Stratified Rotating Shear Flows, PRL, 2013. prl.aps.org/abstract/PRL/v111/i8/e084501

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User comments : 9

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cantdrive85
1.2 / 5 (18) Aug 20, 2013
Expounding upon "models we know are wrong" does little in advancing science. Their goal isn't advancing science, it's all about the gravy train paying for their pseudoscientific mind games.
Q-Star
2.7 / 5 (3) Aug 20, 2013
Oh boyo,,,, "zombie vortices" this should be big fun.
cantdrive85
1.4 / 5 (11) Aug 20, 2013
Got your zombie vortices over heeere!
All we need is a little "ideal" ionizes gas, and voila!
Zombie tornadoes!
Get your zombie vortices over heeere!
barakn
5 / 5 (5) Aug 20, 2013
http://physicsworld.com/cws/article/news/2013/jul/19/attractive-force-arises-from-black-body-radiation-say-physicists points to dispersive forces between particles of cold gas. In most physically realistic cases this attractive "black-body optical force" is greater than the radiation pressure.

Perhaps you ought to learn what 'dispersive' means.
Gmr
4.5 / 5 (8) Aug 20, 2013
Well, with peripherally climate related articles, I know that Nik won't be far behind, a rising, lapping tide of words - and now anything remotely peripheral to astronomy or electromagnetism seems to draw in Electric/Plasma Universe folks like so many iron shavings to a bar magnet.

So, I really have at least two channels for my entertainment needs.
LarryD
3.5 / 5 (2) Aug 20, 2013
I like this bit 'Because the vortices arise from these dead zones, and ........... we affectionately refer to them as 'zombie vortices,.....' 'affectionately' is not quite the word I would think of for any kind of 'zombie'. Wasn't 'Dead Zone' the name of a Canadian TV series?
GSwift7
not rated yet Aug 21, 2013
I thought turbulence in the disk had always been assumed, though too complicated to model. I wonder, what is different about this version of turbulence versus what we already assumed there?

This might explain some of the banding we observe in the disks as well, in stead of planets forming in the disk. That might explain the bands we've seen at distances too far out to be planets too.

If the banding is related to the vortices, as it is on all of our gas giant planets, then that should also lead to sorting of materials, as we see on our gas giants. This is a lot of if's, but that in turn might explain the differences in composition of the planets compared to one another??
GSwift7
not rated yet Aug 21, 2013
Actually, the London Dispersion force is an attractive force. It is the only attractive force between noble gasses. Here's the wiki page:

http://en.wikiped...on_force

I think the term refers to the dispersion of the electrons within the molecules, not the dispersion of the molecules as a whole? If you go past the first paragraph of the wiki page, the explanation gets better. That page starts out kinda confusing.
LariAnn
not rated yet Oct 15, 2013
I'm still wondering where what would seem to be a static gas cloud suddenly acquires enough angular momentum to become a disc and then go on to form vortices. On Earth, the rotation of the Earth influences the formation of atmospheric vortices, but what rotation is influencing the change from static gas clouds to discs to vortices on a proto-solar system? In the atmospheric example, the vortex forms at the surface of a rotating sphere (the planet or the atmosphere). What rotating sphere is present on which the proto-solar system vortices form?