A star born from the same cloud of gas as our sun 4.5 billion years ago has been found at last, astronomers say. This solar sibling is a little bigger than our sun, and a little hotter. But a team of researchers says it has the same chemical fingerprint as the star at the center of our solar system, leading them to conclude both stars were born in the same stellar nursery, at the same time.
"Stars that were born in different clusters have different compositions," said Ivan Ramirez, an astronomer at the University of Texas at Austin and lead author of a paper to be published June 1 in the Astrophysical Journal. "If a star has the exact same chemical composition as our sun, that establishes that they were born in the same place."
Like most stars, our sun emerged from an immense cloud of gas and space dust that gave rise to 1,000 to 10,000 stars. Those baby stars stayed clustered together for hundreds of millions of years — a relatively short time on the astronomical scale.
But as they grew up, their cluster broke up and the individual stars began to drift apart. Billions of years later, these stellar siblings are now scattered across the Milky Way galaxy.
Our sun's newly discovered solar brother from the same gas-cloud mother is known as HD 162826. It is just 110 light years away from our sun, which Ramirez said is remarkably close. "It is almost certain that if there is another star like this one this close to us, we would have found it already," he said, "so the next siblings we find are going to be further away."
Ramirez wasn't expecting to find a solar sibling even this close to our own sun. He said that his original intent was to determine efficient ways of identifying our sun's closest relatives in the future when new data became available. Surveys like space-based telescope Gaia's provide astronomers with a flood of new data.
"There are number of surveys that are happening right now that will allow us to learn more about stars beyond the solar neighborhood," he said. "Right now there are about 100,000 stars we can look at in this way. In five or 10 years it could be as many as a billion."
His plan was to determine which chemical elements would be key in finding solar siblings, and in the process, he and his team actually found a solar sibling. The discovery, and hopefully future ones, should help researchers better understand the origins of our solar system.
"If you track their orbits back in time and find where they intersect 4.5 billion years ago, we can finally see in what part of the galaxy our sun was born," Ramirez said. "We would like to know the environment of the solar system when it was forming, and if it has anything to do with the way things are today."
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