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  • Our galaxy, the Milky Way, is big.

  • Estimates put it at about 100,000 light-years, from one end to the other.

  • But you know what's way bigger?

  • Space itself.

  • Because in all of that space we estimate that there are as many as 100 billion galaxies.

  • And among all those galaxies, we've found a few that are our twins.

  • That's right, the Milky Way has long-lost twins out there among the stars.

  • Although not in a literal sense like our galaxies formed in the same place at the same time.

  • But finding these twin galaxies can help us learn about our own, because it's pretty

  • hard to figure out what's going on in the Milky Way while we're a part of it.

  • The Milky Way's disk is 1,000 light years thick, and to get a good picture of it, you'd

  • have to get pretty far above it, like how the Earth is round but you wouldn't see

  • the curve unless you were way above it, even higher than commercial airliners go.

  • And cue the flat Earthers in the comments.

  • Considering that the Voyager I, the most distant man-made object we've ever made, is about 0.002 light-years

  • away, we're not taking a galactic selfie any time soon.

  • To borrow a metaphor I wish I'd thought of, mapping the Milky Way is like trying to

  • map a forest while you're tied to one of the trees.

  • So we've had to piece together what our galaxy looks like based on what we can see.

  • First and most obvious is the Milky Way is flat because we can see it edge-on in our night sky.

  • The shape of that flat plane has been a bit harder to pin down.

  • The astronomer Herschel was the first to try it in 1785, and by counting the number of

  • stars he saw and assuming that more stars meant more galaxy, he came up with a pretty blobby shape.

  • This picture changed in the 1910s when another astronomer, Harlow Shapley, measured the distance

  • to globular clusters of stars and found that they were in a spherical shape about 100,000 light years in diameter.

  • Shapley concluded that our galaxy must be a circular disk inside this spherical halo of globular clusters.

  • In the last 75 years, techniques that could see through interstellar dust like radio,

  • infra-red, and X-ray astronomy have helped us see just where the arms of our spiral galaxy are.

  • But there's only so much we can do from here.

  • Exactly what the Milky Way looks like on the other side of its central bulge is unknowable to us.

  • And our image of what we can see is still changing; we only started to realize the central

  • bar connecting the large spiral arms was thicker and more substantial than we thought in 1996.

  • So now that we have a pretty good idea what we look like, we can seek out similar galaxies that can fill in the gaps.

  • NGC 1073, for example, is a barred spiral in the constellation Cetus.

  • Another twin, GAMA202627 has two smaller companion galaxies, much like our own Magellanic clouds.

  • Companions as big as these clouds are a rare find and warrant further study.

  • We've even found a galaxy that could tell us about the Milky Way's ominous future.

  • Near Andromeda is a small and incredibly dense galaxy called M32.

  • A recent paper proposes that once upon a time it looked like the Milky Way, until Andromeda

  • came barreling through, stealing stars and planets, ballooning in size, and leaving M32 a shadow of its former self.

  • Why is this important you ask?

  • Because Andromeda is on a collision course with our galaxy.

  • What happened to M32 could be what happens to us.

  • Odds are good that as our telescopes and techniques improve, we'll find more of our twins out there that can tell us more about ourselves.

  • Just don't get too attached to the galaxy's shape, because in about 4.5 billion years, it could all change.

  • Fun Fact: Confirming the Milky Way had a large bar also meant our galaxy had two large arms

  • that wrapped around it twice, rather than four separate main arms as previously thought.

  • If you liked this video, go check out this one Maren did on the universe's first type of molecule.

  • Thanks for watching, don't forget to subscribe and I'll see you next time on Seeker!

Our galaxy, the Milky Way, is big.


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天の川の双子がどのように破壊されたかを発見 (We Just Discovered How the Milky Way's Twin Was Destroyed)

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    Jerry Liu に公開 2021 年 01 月 14 日