Whatever happened to the Sun's missing siblings?

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The Sun was born 4.6 billion years ago inside a nebula that likely gave birth to a thousand other stars. So what happened to the Sun's siblings? The search continues, but they could be practically anywhere in the Milky Way.

A thousand stars seems like an easy enough thing to find, but the Milky Way is actually home to somewhere between 100 and 400 billion stars. Even if all the Sun's sibling stars were clumped together in a single cluster, they'd still be phenomenally difficult to find, and that task is only complicated because they've likely spread themselves throughout the entire galaxy.

Last year, Dutch astronomer Simon Portegies Zwart suggested how we might find the Sun's closer siblings. He modeled how the stars would have dispersed as they orbited around galactic central point, and he determined that about 10 to 60 stars should be within very close range of Earth, no more than 330 light-years. At that sort of distance, a decent pair of binoculars would be adequate to see those stars in the night sky. These stars would share the Sun's age, chemical composition, and motion through space, and these together could mean they would offer useful insight into how our own solar system was born.


If there really are multiple dozens of the Sun's siblings in our cosmic backyard, then finding them should be a piece of cake. But Russian astronomer Yury Mishurov isn't so sure. He argues Portegies Zwart's model wasn't sophisticated enough to yield accurate results, as it didn't account for the effects of spiral arms. These protrusions from the main body of the Milky Way can greatly affect the movement of stars due to the tremendous effect of their gravity.

But Mishurov's new calculations, the Sun's siblings would be much more widely dispersed throughout the Milky Way, with perhaps as little as 3 or 4 stars left in the Sun's immediate vicinity. Portegies Zwart, for his part, welcomes the new research:

"Even though they seem to be quite critical of my previous work, I'm pretty happy with this publication. It was the logical next step. In the end, of course, what counts is whether or not we will find the solar siblings. I think it's a big mistake to give up looking for them."


Admittedly, not all astronomers are convinced on that last point. As Cambridge astronomer Gerard Gilmore points out, it's easy enough to come up with lots of other stars that are just like the Sun, but practically impossible to trace them back to the same birthplace. In that case, even if finding the Sun's siblings would have scientific value, it's unclear whether we could ever find them. Still, I must admit it's very cool to think the Sun might have an identical twin somewhere on the other side of the galaxy, complete with a planetary system very much like our own. It's like the slightly more plausible version of all those pulp sci-fi stories about the Earth's hidden twin.

[arXiv via Science]