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Our Sun probably has a bunch of siblings

ARI SHAPIRO, HOST:

The sun can seem lonely with other stars so far away. They're just specks in space. But our sun wasn't always by itself. Stars are born in clusters. Which means the sun must have siblings. And those siblings are somewhere out there. NPR's Regina Barber talks to two astrophysicists who tried to find them.

REGINA BARBER, BYLINE: When the sun was born, it had thousands of siblings, all born together in a cluster. Star clusters can be seen all over the sky. Take the Pleiades, which you can see with your naked eye. In Japan, it's called Subaru. These groups of stars are born all at the same time from a giant cloud of dust and gas collapsing under its own weight. In this cloud, some of that gas will form dense little pockets. These little pockets will turn into stars. So why is the sun alone now? It's because siblings can drift apart. I talked with Jeremy Webb, a professor and astrophysicist at York University in Toronto.

JEREMY WEBB: You bring three siblings in too close to each other, they really don't like that.

BARBER: The stars' gravitational influence on each other can end up flinging them out of the cluster at really high speeds. Then they orbit by themselves in the galaxy.

WEBB: And those siblings tend to never see each other and never talk to each other again.

BARBER: But even for siblings that don't push each other away, they're still external forces that can pull them apart. For example, here's what can happen when a massive space cloud passes by a star cluster.

NATALIE PRICE-JONES: It does have a gravitational effect on that stellar birth cluster. Like, they have different influences as they're growing up.

BARBER: That's Natalie Price-Jones. She worked with Webb when she completed her Ph.D. studying star clusters. She and Webb like to talk about finding siblings by looking at their DNA.

WEBB: When all these stars - when they're in their birth environment, when they're in their cluster, you can think of them as sharing all the same DNA and that they're all made out of the same stuff. They're all moving inside the clusters. So their positions, their velocities, their speeds, that's all quite similar.

BARBER: When Webb says same stuff, he means chemical properties of the star. The gas and dust that make up the star have certain amounts of helium, carbon, iron, gold. And this composition of elements can be specific to a certain star cluster. Here's Price-Jones again.

PRICE-JONES: The gas that stars are made of can be polluted by other stars exploding. So that's how we get kind of more unique chemical signatures.

BARBER: So we have their DNA. This means we can find thousands of sun siblings out there, right? Here's the problem. Webb says some of the DNA has changed. Their speeds and locations have shifted over time. And that's because the sun siblings have lived full lives since they were all born 4.6 billion years ago. He and Price-Jones did their best to figure out how much of a change was reasonable using computer simulations. And Price-Jones says they ruled out a lot of candidates.

PRICE-JONES: These stars, you know, even though they might look eligible from a chemical perspective, there's just no way that they could have reasonably moved to the distribution they are and be affiliated with the sun's birth cluster.

BARBER: She and Webb ended up finding one star they think could be the sun's sibling. Other researchers have found a handful of other possible candidates. But either way, considering that the sun was born with thousands of siblings, that's not a whole lot. So in the end, I asked, why even do it? Why look for the sun siblings? The answer they gave was simple - the search for life.

PRICE-JONES: If we could find other stars that were born in the same cluster as the sun, they might have had the same conditions that allowed the sun to have a planet that supports life. You know, are we alone out there? Or are there other planets like ours that are hosting other radio interviews?

BARBER: Maybe one day a sun sibling will help us find a place just like us, full of life. Regina Barber, NPR News.

(SOUNDBITE OF THE BEATLES SONG, "HERE COMES THE SUN") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Regina G. Barber
Regina G. Barber is Short Wave's Scientist in Residence. She contributes original reporting on STEM and guest hosts the show.