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  • Thanks to Brilliant.org for supporting SciShow Space.

  • [♪ INTRO]

  • Space is packed with all kinds of mysteries; that's part of what makes it cool.

  • Some of those mysteries, though, are closer to home than others.

  • Like, here's a surprising one: We actually don't know where the Sun came from!

  • According to what we know about star formation, the Sun probably formed from a huge cloud

  • of gas, along with a bunch of stellar siblings, stars that formed in the same place out of

  • the same stuff.

  • Except, we can't find evidence of that cloud, or the Sun's family, anywhere.

  • Our little Sun is all on its own.

  • Get your tissues ready, because this is basically waiting to be turned into a Pixar short.

  • Even though we can't find the Sun's family, we're pretty confident it has to exist because

  • of how most stars form.

  • The current model requires that a bunch of stars get born together out of a big ol'

  • gas cloud, called a molecular or giant molecular cloud depending on its size.

  • Eventually, because space is super vicious, the clouds get eaten up or dispersed by their

  • star children.

  • After that, the stars, and their planets, if they've accumulated any, might separate

  • or might move together for a while in a so-called open cluster.

  • Then, over time, all the little gravitational pulls and tugs from the member stars build

  • up and finally send the stars on different trajectories.

  • These stars can end up all over a galaxy, but they can still be identified as members

  • of the same family because they typically have similar ages, and often have really similar

  • compositions.

  • There can be plenty of variation within a cluster, but there are still some general

  • trends we can look for.

  • Most stars don't stick around to form open clusters, but we have evidence that the Sun

  • was one of the few who stayed with its family a bit longer.

  • For one thing, the orbital motions of the Kuiper Belt objects, most notably the planetoid

  • Sedna, strongly suggest some gravitational interaction with other stars, probably in

  • a relatively dense group.

  • Otherwise, they likely couldn't have been jostled into their current orbits.

  • There's also evidence, like the excess amount of heavy elements in the Sun, and the presence

  • of uranium in the Earth, that there was a supernova near our star when it formed.

  • It could've come from a huge, short-lived member of a larger stellar nursery, like an

  • older sibling who peaked too early.

  • We have plenty of reason to believe that the Sun was born in an open cluster, but we can't

  • find anyone else from that stellar nursery, even though we've been looking all over.

  • It's like Finding Dory, but with a lot more math.

  • For a while, astronomers thought the Messier 67 open cluster, or M67 for short, was the

  • most likely candidate.

  • It's an open cluster about 2700 light years away, in the Cancer constellation.

  • It's a pretty dense group, which would match our hypotheses, and it's also about five

  • billion years old.

  • That's really old for an open cluster, but it's about as old as the Sun!

  • Admittedly, dating stars is really hard, so there are some big error bars on that measurement.

  • But it's in the ballpark, and astronomers love ballparking.

  • So its age and density make M67 a good candidate, but its orbital path around the galaxy is

  • way different from the Sun's, and that's become a big source of debate.

  • On the one hand, this might not be a problem.

  • Because members of open clusters interact gravitationally, it's possible that a star

  • could get kicked out and end up with some different orbital parameters.

  • But on the other hand, the kind of kick that the Sun would have needed to get on its current

  • path is super huge, like, too big for it to have kept its baby solar system.

  • So the fact that we're here is some evidence against the M67 hypothesis.

  • That is, unless that kick happened really early on.

  • An early, gentle nudge, given a lot of time, could have gotten the Sun way off course.

  • So, we're still not exactly sure what's going on here!

  • What we could really use is more data.

  • Thankfully, there are a few projects, both launched in 2013, that are helping with that.

  • One is the Gaia mission, run by the European Space Agency, and the other is the GALAH project,

  • run by the Australian Astronomical Observatory.

  • Together, they're collecting astrometry and astrochemistry data of a truly enormous

  • quantity of stars, or data about their positions, movements, and chemistry.

  • Astrometry is good for finding former and current open clusters, because members of

  • them move together.

  • And even if the Sun's siblings have dispersed, we could use current star positions to calculate

  • the cluster's original location.

  • Astrochemistry may also prove to be a smoking gun.

  • Since the Sun is so metallic from that supernova explosion, its sibling stars may have similarly

  • high metallicities.

  • All we have to do is find stars that match those descriptions!

  • Gaia is working to get astrometric and astrochemical data on a /billion/ stars from an orbit near

  • Earth.

  • GALAH, on the other hand, is just doing astrochemistry on a more modest million stars, and it's

  • operating from the ground.

  • Both missions will wrap up over the next few years.

  • After that, it's up to astronomers to make sense of the mountains of data!

  • Between the two surveys, we're characterizing tons and tons of stars.

  • We haven't found the Sun's siblings yet, but these surveys are currently our best chance

  • at it.

  • Besides being a nice end to a story, understanding where the Sun originated and what it was like

  • there can also help us understand why our solar system turned out like it did.

  • Still, even if these projects don't give us the data we need to solve the Sun's mystery,

  • they'll give us incredible insights into the formation and evolution of the galaxy,

  • which is a pretty sweet consolation prize.

  • But there are some puzzles we can solve about where stars come from on Brilliant.org.

  • That's right, they have a whole course on the Life Cycles of Stars which starts with

  • this Star Formation quiz.

  • What's cool about Brilliant is that they've really embraced how to best use their platform

  • with animations that help you wrap your brain around a complex idea.

  • When I was going to school and regularly taking science quizzes, we didn't have the internet

  • or computers in the classroom, because I'm old.

  • We had this stuff called paper and it didn't include moving graphics like this that help

  • you imagine the problem.

  • But with Brilliant, whether you're a student or a lifelong learner, you can benefit from

  • these interactive quizzes to help you learn and have fun while you're doing it.

  • So check it out and see how much you know about star formation.

  • Brilliant is also offering 20% off their annual premium subscription to the first 200 SciShow

  • Space viewers who sign up at Brilliant.org/SciShowSpace.

  • So you'll get a discount, and be helping to support SciShow Space.

  • So thanks! You are awesome!

  • [♪ OUTRO]

Thanks to Brilliant.org for supporting SciShow Space.

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