Mixing in star-forming clouds explains why sibling stars look alike

Aug 31, 2014
This is an image from a computer simulation shows a collision of two streams of interstellar gas, leading to gravitational collapse of the gas and the formation of a star cluster at the center. In this image, the gas streams were labeled with blue and red "tracer dyes," and the purple color indicates thorough mixing of the two gas streams during the collapse. Credit: Y. Feng and M. Krumholz

The chemical uniformity of stars in the same cluster is the result of turbulent mixing in the clouds of gas where star formation occurs, according to a study by astrophysicists at the University of California, Santa Cruz. Their results, published August 31 in Nature, show that even stars that don't stay together in a cluster will share a chemical fingerprint with their siblings which can be used to trace them to the same birthplace.

"We can see that stars that are part of the same star cluster today are chemically identical, but we had no good reason to think that this would also be true of stars that were born together and then dispersed immediately rather than forming a long-lived cluster," said Mark Krumholz, professor of astronomy and astrophysics at UC Santa Cruz.

Our sun and its siblings, for example, probably went their own ways within a few million years after they were born, Krumholz said. The new study suggests that astronomers could potentially find the sun's long-lost siblings even if they are now on the opposite side of the galaxy.

Krumholz and UC Santa Cruz graduate student Yi Feng used supercomputers to simulate two streams of interstellar gas coming together to form a cloud that, over the course of a few million years, collapses under its own gravity to make a cluster of stars. Studies of show much greater variation in chemical abundances than is seen among stars within the same open star cluster. To represent this variation, the researchers added "tracer dyes" to the two gas streams in the simulations. The results showed extreme turbulence as the two streams came together, and this turbulence effectively mixed together the tracer dyes.

"We put red dye in one stream and blue dye in the other, and by the time the cloud started to collapse and form stars, everything was purple. The resulting stars were purple as well," Krumholz said. "This explains why stars that are born together wind up having the same abundances: as the cloud that forms them is assembled, it gets thoroughly mixed. This was actually a bit of a surprise. I didn't expect the turbulence to be as violent as it was, so I didn't expect the mixing to be as rapid or efficient. I thought we'd get some blue stars and some red stars, instead of getting all purple stars."

This video is not supported by your browser at this time.
This computer simulation shows the collision of two streams of interstellar gas, leading to gravitational collapse of the gas and the formation of a star cluster at the center. The left side shows the density of interstellar gas (redder indicates higher density), and the right side shows the two "tracer dyes" added to show how the gas from the two streams mixes together during the collapse. Circles indicate stars. Credit: Y. Feng and M. Krumholz

The simulations also showed that the mixing happens very fast, before much of the gas has turned into stars. This is encouraging for the prospects of finding the sun's siblings, because the distinguishing characteristic of stellar families that don't stay together is that they probably disperse before much of their parent cloud has been converted to stars. If the mixing didn't happen quickly enough, then the chemical uniformity of would be the exception rather than the rule. Instead, the simulations indicate that even clouds that don't turn much of their gas into stars produce stars with nearly identical chemical signatures.

This is an image from a computer simulation shows a collision of two streams of interstellar gas, leading to gravitational collapse of the gas and the formation of a star cluster at the center. Colors represent the density of interstellar gas (redder indicates greater density). Credit: Y. Feng and M. Krumholz

"The idea of finding the of the sun through chemical tagging is not new, but no one had any idea if it would work," Krumholz said. "The underlying problem was that we didn't really know why in clusters are chemically homogeneous, and so we couldn't make any sensible predictions about what would happen in the environment where the Sun formed, which must have been quite different from the environments that give rise to long-lived star clusters. This study puts the idea on much firmer footing and will hopefully spur greater efforts toward making use of this technique."

This video is not supported by your browser at this time.
This 11-second movie shows a computational simulation of a collision of two converging streams of interstellar gas, leading to collapse and formation of a star cluster at the center. Face-on view shows the plane where the two gas streams meet. Numbers rapidly increasing at upper left shows the passage of time in millions of years. Left panel shows the density of interstellar gas (yellow and red are densest) and right panel shows red and blue "tracer dyes" added to watch how the gas mixes during the collapse. Circles outlined in black are stars; stars are shown as white in the left panel, and in the right panel their color reflects the amount of the two tracer dyes in each star. The simulation reveals that gas streams are thoroughly homogenized within a very short time of converging, well before stars begin forming. Credit: Mark Krumholz/University of California, Santa Cruz


Explore further: Lives and deaths of sibling stars

More information: Yi Feng, Mark R. Krumholz. Early turbulent mixing as the origin of chemical homogeneity in open star clusters. Nature doi:10.1038/nature13662 (2014).

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cantdrive85
2 / 5 (8) Aug 31, 2014
G-g-g-g-gigo..."Streams" of interstellar gas will in fact behave as a plasma affected/directed by EM fields, this simulation is meaningless.

The reason "families" of stars resemble one another is likely due to Marklund convection ordering the constituent parts of the Birkeland currents the stars reside within.
FineStructureConstant
2.6 / 5 (5) Aug 31, 2014
The reason "families" of stars resemble one another is likely due to
...Snake oil.
DeliriousNeuron
1.6 / 5 (7) Aug 31, 2014
Why do they keep running gravity based simulations since we all know gravity is the weaker force?
I can't wait until we get out of the dark ages of Science. Yawn....
Cantdrive has the better theory here.
IMP-9
4.4 / 5 (7) Sep 02, 2014
Why do they keep running gravity based simulations since we all know gravity is the weaker force?


It's not weaker on the largest scales. Electric forces fall off much faster than r^2 in a plasma because of Debye shielding.

"Streams" of interstellar gas will in fact behave as a plasma


Which behave as a fluid on the largest scales. There simulation is fine.
cantdrive85
1 / 5 (5) Sep 03, 2014
It's not weaker on the largest scales. Electric forces fall off much faster than r^2 in a plasma because of Debye shielding.

That's your claim based upon already failed hypotheses.

News flash......... Dateline 1958.......
This just in, decades ago, every space age in situ measurement has shown the near Earth and solar system plasma to require a complete re-write to the behavior of said plasma. From the acceptance of Birkeland's aurora models to Alfven's mostly correct models of magnetospheric circuits it's been shown the ionized gases of MHD theory to be a complete failure. BTW, let's not forget large scale magnetic fields which MUST accompany a large scale electric field.
http://www.univer...-fields/
Which behave as a fluid on the largest scales.

Of course, you require the physics must be different.

There simulation is fine.

Did you forget a word?
Should it read; "That there simulation is real...dagnabit!"

Let's try joining the 21st century and real plasma physics rather than theory.
IMP-9
4.4 / 5 (7) Sep 03, 2014
That's your claim based upon already failed hypotheses.


Debye shielding doesn't come from MHD. Once again you demonstrate a total lack of understanding. MHD explicitly does not work on such small scales as The Debye length. Birkeland currents can actually be simulated in MHD, they do not prove it wrong.

So again electric fields fall off faster than r^2 and no you don't need large scale electric fields. They can be suppressed and yet the magnetic field is not.
no fate
1 / 5 (6) Sep 03, 2014
"This is an image from a computer simulation shows a collision of two streams of interstellar gas, leading to gravitational collapse of the gas and the formation of a star cluster at the center."

LMAO...Find it in space as it is shown in the simulation.