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Our sun once had thousands of sibling stars. Where did they go? : NPR

April 18, 2024
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The sun sits alone at the center of our solar system — but it was actually born in a giant cloud alongside thousands of other stars. So where did all those stars go?

The Science of Siblings

Astrophysicists Jeremy Webb and Natalie Price-Jones explain what may have happened to the sun’s siblings — and why finding them matters.

Our sun sits alone in our solar system, surrounded by planets and the vast darkness of space. But when it was born, it lived crowded next to thousands of its siblings. Where did they go?

 

Jeremy Webb is an assistant professor at York University in Toronto, who explores how gravity has shaped our universe. He is a 38-year-old white man with a beard. He says, "If we can find as many siblings as we can, things that formed the same way and in the same places as our sun, that ... increases our ability to answer those really big questions like, 'Why are we here?' 'Why are we alone?'"

 

Stars are born together in a giant cloud of dust and gas: a stellar nursery. This cloud curls in the sky, resembling yellow mountains and valleys dotted by stars. This dust isn't like the kind that collects under your bed, like little gray dust bunnies.

 

"We're talking about little, little solid objects, micrometers in size, that hang out along with the gas molecules," says Webb. Behind him, a panel zooms in on a tiny gray speck that's 1 micrometer in size, out of a stellar nursery hundreds of light-years in size. For reference, 1 light-year is about 6 trillion miles, while 1 micrometer is one-millionth of a meter.

 

As these clouds shrink due to gravity, they form many dense, little clumps that collapse down to make clusters of multiple stars. One cluster is the Pleiades, which in Japan is called Subaru, which is represented in the Subaru car logo.

 

Despite their shared origins, these sibling stars usually don't look alike. For example, these stars differ in color and size: Yellow dwarfs and red dwarfs are small, while blue giants are much larger. And just like human siblings, their interactions can cause them to drift apart.

 

Star siblings can encounter another cloud of gas, and the gravity of that cloud can affect various stars differently. Natalie Price-Jones is a 30-year-old white woman with mid-length straight brown hair. She researched star siblings with Webb for her Ph.D. "They have different influences as they're growing up that can also cause them to end up on different orbits in the galaxy," she says.

 

Other times, some siblings might move too close as they orbit each other. As a result, they can eject out of the cluster at high speeds to end up by themselves in the galaxy. "And those siblings tend to really never, never see each other and never talk to each other again," says Webb.

 

Researchers have identified only a handful of stars that could be our sun's siblings. Among them are HD 162826, which was identified in 2014; HD 186302, which was identified in 2018; and 2mass j19354742+4803549, which was identified by Webb and Price-Jones in 2020. The first two are similar in size to our sun, while 2mass is estimated to be anywhere from 10 to 100 times bigger.

 

Since the sun's siblings likely don't look the same, researchers look for similarities in their "DNA": chemical properties like hydrogen, helium, carbon and iron. Other similar characteristics could be orbital speed, like two stars traveling in the same direction, or location, like two stars in a similar location in space.

 

It's a difficult task — the sun was born about 4.6 billion years ago, and its siblings have lived full lives since then. But if we find them, they might have had the same conditions that allowed the sun to support life on Earth. And that could help us solve the greatest mystery of all:

 

"Are we alone out there?" Price-Jones asks. She and Webb stand in a crowd of people in a city, looking up into the vast night sky dotted full of stars.

 

This comic was written and illustrated by Connie Hanzhang Jin, based on reporting from Regina Barber and Connie Hanzhang Jin. It was edited by Amina Khan, Ben de la Cruz and Pierre Kattar.

The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health all the way down to our very molecules. We’ll be sharing these stories over the next several weeks.

More from the Science of Siblings series:

  • A gunman stole his twin from him. This is what he’s learned about grieving a sibling
  • In the womb, a brother’s hormones can shape a sister’s future
  • These identical twins both grew up with autism, but took very different paths



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