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  • Thanks to Brilliant.org for supporting SciShow Space.

  • [ ♪ Intro ]

  • The Milky Way is our home, so you'd think we'd know a lot about it.

  • And we do.

  • But a whole galaxy is a pretty big place, so there's still plenty of weird stuff that

  • we're trying to figure out.

  • And that's the cool stuff!

  • So, here are three questions scientists are still trying to puzzel out.

  • One is our galaxy's shape.

  • We know that we live in a spiral galaxy, with long, sweeping arms packed with stars.

  • But why's it like that?

  • After all, stars form from a fog of gas and dust called the interstellar medium, or ISM.

  • And the ISM is everywhere within the galaxy, so why do stars congregate in the arms?

  • Well, we don't totally know -- but we're making progress.

  • One clue comes from structures called filaments that astronomers in the 1980s started to find

  • at the cores of some galactic arms.

  • Filaments are dense regions of the ISM that are incredibly thin, up to a hundred times

  • longer than they are wide.

  • They can stretch for hundreds of light-years but, weirdly, seem to exist on all size scales,

  • kind of like a fractal.

  • Together, they form a sort of galactic skeleton for the Milky Way, providing ingredient-rich

  • places for new stars to form.

  • The European Space Agency's Herschel Space Observatory has even found filaments connecting

  • all the closest star forming regions!

  • But exactly how many of these structures there are and how they play a role around here is

  • still up for debate.

  • That's not the only mystery our galaxy's stars present.

  • As astronomers have mapped out the positions and speeds of nearby stars more accurately,

  • they've found they're less predictable than expected.

  • Instead of mostly circling in a flat plane, a research group discovered in 2012 that many

  • stars seem to be moving up or down about 10% as fast as they're circling the galactic center.

  • When mapped out at large scale, the Milky Way's stars even seem to be rippling with waves.

  • Studying these waves is called galactoseismology and, like the study of seismic waves here

  • on Earth, it may reveal clues about unseen events.

  • The waves are probably the result of a big collision with the Milky Way... but where's the collider?

  • Researchers aren't sure, but they think there are two likely possibilities, both of

  • which would've happened about 100 million years ago.

  • One's kind of standard: an interaction between our galaxy and one of its many satellite galaxies.

  • The other, though, is really cool: It's possible that the Milky Way collided with

  • a massive dark matter structure, and its gravity stirred up all those stars.

  • Although we can't see dark matter, we know it's all around us, especially near our

  • galaxy's outer edges.

  • But just because we can't find the culprit, doesn't mean it's gotta be dark matter.

  • Whatever the collision was, its trajectory probably carried the other object to a place

  • beyond the galactic core and basically out of sight from Earth.

  • There's also at least one piece of evidence suggesting a dwarf galaxy might've been

  • the culprit instead.

  • Astronomers have found a few stars traveling so fast that they couldn't have come from

  • our galaxy, so they might have been knocked loose during that big collision.

  • Either way, we'll have to work fast to figure this out because those waves of stars will

  • probably disappear in another hundred million years.

  • Then again, maybe we won't have to work that fast after all.

  • Finally, stars aren't the only thing traveling weirdly fast around here.

  • For decades, astronomers have observed a few clouds of gas moving at strangely high velocities

  • -- up to 90 kilometers per second faster than the stuff around them.

  • At that speed, it would take only a year and a half to travel from the Sun out to Neptune!

  • Always on the lookout for a clever name, researchers call them high-velocity clouds.

  • These clouds are mostly found in the outer, halo region of the Milky Way, and they're

  • often observed to have a low metallicity, or abundance of heavier elements.

  • And they're not small, either: They can contain millions of times more material than

  • the Sun and span tens of thousands of light-years.

  • Scientists have four main ideas about where they might have come from:

  • [yawn ort] The oldest hypothesis, proposed by famous

  • astronomer Jan Oort, suggests that the clouds might be the far-flung leftovers of the process

  • that formed the Milky Way.

  • With only the weakest gravitational pull affecting them, that far-off material would've taken

  • billions of years to get here, speeding up along the way.

  • Another idea is that -- because they do have such low metallicity -- high velocity clouds

  • are the remnants of an ancient collision between the Milky Way and another galaxy.

  • Hey, where have we heard that before?

  • A related hypothesis is that the material is made up of gas stolen gravitationally from

  • a satellite galaxy.

  • That seems especially likely for the clouds found in the southern hemisphere, which is

  • in the direction of the Magellanic Clouds, our closest galactic neighbors.

  • One last idea is that these clouds actually came from the Milky Way all along.

  • Perhaps a powerful supernova explosion hurled them away from the galaxy's disk, only for

  • gravity to claw them back before they could fully escape.

  • There's even a chance different clouds could have different origin stories.

  • To figure that out, astronomers are studying the composition of each cloud in detail.

  • If they were created in different ways, there might be a signature of their home still waiting

  • to be detected.

  • We'll just have to wait for the results.

  • We don't yet know the answers to any of these Milky Way mysteries or many others out there.

  • But put them all together and our galaxy suddenly seems a lot less isolated and our cosmic neighborhood

  • a lot busier.

  • Just watch out for any flying galaxies.

  • One place within the milky way where we can figure out the answers to big questions relatively

  • quickly is Brilliant.org.

  • Inspired by these existing questions about the milky way, I'm working on the Dark Matter quiz.

  • Leading up to it was a lesson and quiz on the fate of the universe that I looked through

  • to prep, but this starts off pretty easy.

  • So this question wants to know what is the dominant source of mass in our solar system.

  • So the Sun!

  • So I got it right and so did 72% of the other people in the Brilliant community.

  • Which is a neat thing about Brilliant because you can see how you did but also see how other

  • people did when they answered the question.

  • I think what sets Brilliant apart from other education sites is this community aspect.

  • On Brilliant you can answer questions that other people have submitted or you can even

  • submit your own questions to be answered.

  • So check it out for yourself and let us know if you submit a question and I'll try to solve it.

  • And the first 777 people to use that url to sign up for an annual premium subscription

  • will get 20% off.

  • Plus, you'll be helping to support SciShow Space when you do, so thank you!

  • [ ♪ Outro ]

Thanks to Brilliant.org for supporting SciShow Space.

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B1 中級

關於銀河系,我們還有3件事情不瞭解。 (3 Things We Still Don't Understand About the Milky Way)

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    林宜悉 發佈於 2021 年 01 月 14 日
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