Four and a half billion years ago, the Sun pulled itself together from gas collapsing inside a giant molecular cloud, but it didn't do it alone. It was born in a star cluster with thousands of other stars, all at the same time and from the same cloud.
This means our favorite star may have thousands of solar siblings, many of them probably just like it elsewhere in the galaxy.
The trouble is... We're not sure where they are.
Most star clusters break apart after less than 100 million years, scattering their stars far and wide, and many astronomers are interested in finding our solar siblings. This is because we still don't know why exactly life was able to develop here on Earth. However, if it was something during the birth of the Solar System that helped life to take hold, then those properties could be shared by our star's fellow litter-mates.
And scientists have a few tricks up their sleeves that may help our star connect with the rest of its brood.
For one thing, every star has a particular chemical fingerprint, or a tag - a specific pattern in its spectrum that tells us how much iron there is relative to hydrogen, or how much of other elements, like aluminum or carbon, there is relative to iron. And stars that are formed from the same cloud are expected to have the same basic fingerprint.
But the abundance of some elements can change over the lifetime of a star, so not every element is useful in fingerprinting stars.
Recently, a group of astronomers found that the abundances of sodium, aluminum, vanadium, and barium all form distinct patterns in stars, and their abundances don't seem to change during stars' lifetimes.
Other stars that have the same relative abundance of those elements as the Sun could be possible solar siblings. But there are a lot of stars out there, so just having matching chemical fingerprints isn't enough.
To be considered a true solar sibling, a star also has to be the same age as the Sun. And the age of an isolated star is actually really tricky to measure, so usually our age estimates have a big margin of error.
Then, a solar sibling star should also have the same dynamic origin as the Sun, meaning that if you trace the orbits of the two stars backward, it would put them in the same place at the same time when they were very young.
Applying all these criteria together, the astronomers recently found one star that seems to meet all of these criteria.
It has the same chemical fingerprint, it is about four and a half billion years old, and it would have been close enough to the Sun over four billion years ago that they could have come from the same star cluster.
That star, probably the first of our rediscovered solar siblings, is called HD-162826. It's a little bit bigger than the Sun - about 1.15 times as much mass - and today, it's around 110 light years away, toward the constellation Hercules.
Unless you're in really dark skies and have amazing vision, it is too faint to be seen with the naked eye. But it's a roughly sun-sized star that's reasonably close, so astronomers have been keeping an eye on it to see if it has planets.
For now, this is the only star that matches all the criteria of a long-lost solar sibling, but there could be more than a thousand others out there. We're just waiting to find them. And when we do, we will be eager to discover whether there's anyone around those solar siblings, waving back.
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Sources: This story was originally published on SciShow Space. I am republishing a lightly edited version on SkyFeed in light of interest in the subject. Green, Hank. "Does the Sun Have Long-Lost Siblings?" SciShow Space, YouTube. 6 Jan, 2015. Web video.
Citation: Rovira, Lia N. "The Sun Has a Long, Mysterious Family History." SkyFeed. 30 May 2018. Web article.