Our Sun Probably Grew Up With a Sibling

But now its buddy is long gone

Proto Stars
Researchers now think that most stars—like this pair in the Perseus constellation—form in pairs. NASA, ESA and J. Muzerolle, STScI

What if every star had a twin? The idea may sound farfetched, but it’s intrigued scientists for years. And when a pair of researchers went looking for the secrets of stars like the sun, reports Mike Wall for Space.com, they learned that Earth’s sun probably once had a twin-like star to call its own.

Sarah Sadavoy of the Smithsonian Astrophysical Observatory paired up with a Berkeley astronomer, Steven Stahler, to try to figure out the secrets of binary stars. They describe their findings in a study in the journal Monthly Notices of the Royal Astronomy Society.

Binary stars and systems that contain multiple stars are pretty common in the Milky Way. But are they born that way? Yes, the new study suggests. The team used observations from telescopes in Hawaii and New Mexico to study the constellation Perseus, which contains a huge molecular cloud thought to contain the building blocks of stars.

The study was all about proportions. When the team assessed the positions of stars in relation to one another, they found that stars separated by a long distance—at least 500 AU, or 46,500 million miles—were much younger than those separated by shorter distances. Then they ran a series of statistical models, which suggested that stars likely first form in pairs. Over time, the majority of these duos break up and go their own ways. Others shrink down into a more compact system. But most of the systems studied seemed to have been born as binaries.

This has an intriguing implication for our closest star, the sun. Scientists have long wondered if it once had a twin star that later died. And this latest study lends support to the idea that our single sun was born with a twin, which as been dubbed “Nemesis.”

“We are saying, yes, there probably was a Nemesis, a long time ago,” says Stahler in a press release. Since the new model shows that twinned stars in wide binaries usually break apart within a million years, it’s likely that Nemesis broke up with the sun at some point and went to live elsewhere in the Milky Way.

Will we ever find Nemesis? That isn’t yet clear. But for now, the data does more than point to a one-time companion to our star. As Sadavoy notes in the release, it’s important to look at star formation to learn more about the history of the universe. “This is going to change our understanding of dense cores and the embedded stars within them,” says Sadavoy—whether or not we ever unravel the final destination of the sun’s one-time sibling.

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