Why Sibling Stars Look Alike: How to Track Down the Sun's Sisters

Why do sibling stars look alike? Scientists have found that the similarities of stars in the same cluster are the result of turbulent mixing in the clouds of gas where star formation occurs.

"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, one of the researchers, in a news release.

Our sun and its siblings went their separate ways within a few million years after they were first formed. In theory, this new study means that scientists could track down our nearest star's wayward siblings in order to reconstruct what happened during the formation of our galaxy.

In order to learn a bit more about star formation, the researchers used computer models to simulate two stream 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. The scientists incorporated variation in chemical abundances by adding "tracer dyes" to the two gas streams in the simulations. The results revealed extreme turbulence as the two streams came together and mixed.

"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," said Krumholz. "The resulting stars were purple as well. 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."

The findings reveal that mixing occurs rapidly and may mean that scientists could track down the star's siblings. Even clouds that don't turn much of their gas into stars produce stars with nearly identical chemical signatures, which means that scientists could follow our own sun's chemical signature in order to find similar stars.

The findings are published in the journal Nature.