Our Sun May Have Had a Twin

This is a sad story about lost siblings.

The sun may be the lone star in our solar system today, but that may not have always been the case. Scientists at UC Berkeley and Harvard University say they've found proof that most stars form in pairs or even as triplets. However, they don't always stay together for their whole existence. The research has been accepted by the Monthly Notices of the Royal Astronomical Society.

Close, but Not Too Close
Scientists have known for a while that some stars have companions while others don't. To figure out what could be behind the variation, the teams zeroed in on Perseus, what they call a typical constellation. They used data from a survey called VANDAM that categorizes all of the young stars making up Perseus. Remember, in galaxy terms, we're talking less than four million years old.

The researchers found 45 single-star systems, and 55 stars in multiple-star systems. Five of those in multiple-star systems were not binary. They used statistics to try to explain this.


This is a radio image of a very young binary star system, less than about 1 million years old, that formed within a dense core (oval outline) in the Perseus molecular cloud. All stars likely form as binaries within dense cores.
Image: SCUBA-2 survey image by Sarah Sadavoy, CfA.
"The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion," according to a Berkeley media release. The researchers say this is an important next step to take knowledge beyond computer simulations.

Although they're considered binary, these stars aren't identical, or even geographically very close to one another. The researchers noted pairs were at least 500 times further away from each other than the Earth is to the sun (on average).



This infrared image from the Hubble Space Telescope contains a bright, fan-shaped object (lower right quadrant) thought to be a binary star that emits light pulses as the two stars interact.
Image: NASA, ESA and J. Muzerolle, STScI
Companion Stars and Dinosaurs
In our solar system, this means what some call the twin of the sun, known as Nemesis, could really have existed. The researchers think if it did exist, Nemesis "escaped" long ago and is somewhere else in the Milky Way.

In a piece for The Conversation, Lancaster University's Konstantinos Dimopoulos addressed the issue. According to the scientist, while most accept that a comet or an asteroid is to blame for killing the dinosaurs, there isn't full agreement on what caused the asteroid or comet to hit. Could the sun's former companion star be the culprit?

"Every 25 million years or so, it makes a pass closer to the sun, which could result in enhanced comet activity, because of its gravitational pull," Dimopoulos wrote of common thinking surrounding the rumored Nemesis. "This is not an unreasonable hypothesis, since the majority of stars belong to systems with multiple stars. However, brown dwarfs are relatively uncommon, and Nemesis has not been observed (yet)."

So the next time you look up at the sun (don't do that or you'll go blind, but we digress), give thanks for that lonely star that gives us life, even though its possible twin abandoned it long ago.

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Learn more about the residents of our solar system in "Solar System: An Exploration of the Bodies that Orbit the Sun" by Marcus Chown. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

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