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  • [♪ INTRO]

  • If you've ever looked up at the night sky,

  • you've probably noticed the constellation of Orion the hunter,

  • whose one shoulder is marked by a bright red star called Betelgeuse.

  • It's one of the most recognizable stars in the night sky.

  • The thing is, these days, it's starting to look a little funny.

  • It's always been super bright because it's just 650 light-years away

  • and it's mind-bogglingly big.

  • Seriously, our solar system out to Jupiter would fit inside of it.

  • That tells us this star is a red supergiant, meaning it's at the end of its life,

  • and scientists believe it's the closest star to Earth ready to explode in a massive supernova.

  • But since last year, scientists have noticed that Betelgeuse is dimming,

  • and not just a little. It's gone from the 11th-brightest star in the sky to the 24th.

  • That's enough to notice with the naked eye!

  • And just last week, thanks to observations from the European Southern Observatory,

  • we learned that this dimming is kind of lopsided.

  • Which has got people talking about how close Betelgeuse might actually be to that explosion.

  • The lopsidedness is especially weird, since astronomers usually think of stars

  • as objects that basically look the same from every side.

  • But that's definitely not the case here.

  • Because Betelgeuse is so big and so close,

  • astronomers can study it in ways that are impossible for almost any other star.

  • For instance, powerful modern telescopes, like Europe's Very Large Telescope,

  • can take pictures directly of its surface.

  • And when a team of researchers recently compared images of Betelgeuse

  • taken in January and December of 2019, they found a remarkable difference.

  • The January image, which was snapped before the recent dimming,

  • shows a star that's pretty symmetric-looking.

  • But in the more recent photo, it's definitely looking crooked.

  • Astronomers have a couple of ideas why.

  • One has to do with the star's size.

  • Because it's so big, the gravity at the surface of Betelgeuse is pretty weak.

  • That means elements in its outer layers can drift away easily,

  • producing massive clouds of dust.

  • Just like on a hazy day, that dust could be obscuring our view of the star.

  • Another possibility is that the whole bottom part could be covered in one giant sunspot.

  • Sunspots are really just cooler parts of a star's surface,

  • which causes them to shine less brightly than the surrounding material.

  • On the Sun, spots never get even remotely close to that big,

  • but the physical processes happening on Betelgeuse could just be totally different.

  • Either way, this new image suggests that the dimming

  • probably isn't a sign that Betelgeuse is about to explode.

  • Which is kind of too bad, since Betelgeuse is far enough away from Earth to be safe,

  • but close enough that its explosion would shine as brightly as the full Moon.

  • Which would be awesome for science but not so great for its close neighbors.

  • While we're not expecting fireworks from Betelgeuse anytime soon,

  • scientists will stay busy exploring a whole new trove of data

  • from NASA's New Horizons spacecraft.

  • Back on January 1st, 2019, the spacecraft flew by a tiny Kuiper Belt Object called Arrokoth,

  • which meansskyin the language of the Powhatan tribe of Native Americans.

  • It took a while to sort out its name,

  • so you might've heard this object called MU69 or Ultima Thule in the past.

  • It orbits more than a billion kilometers past Pluto,

  • making it the farthest object ever explored by a spacecraft.

  • New Horizons collected most of its data over about 12 hours as it zipped past,

  • but it took the better part of a year to radio that information back to Earth,

  • so most of the findings are just starting to come out.

  • In a series of three papers published last Thursday in the journal Science,

  • mission scientists shed light on how Arrokoth and other Kuiper Belt objects may have formed.

  • The key was Arrokoth's unique snowman-like shape.

  • It's made up of two lobes that are neatly stuck together.

  • And astronomers already knew that the two parts

  • must have formed separately before colliding, but how that happened was a puzzle.

  • In one of the recent papers, computer simulations showed that,

  • to avoid cracking the two lobes of the snowman, the collision had to be really slow,

  • under about 18 kilometers per hour.

  • Amazingly, that small detail about the conditions at the time of Arrokoth's formation

  • might have answered a big question about how planets form.

  • See, Arrokoth is an example of a planetesimal,

  • the basic building block of larger planets,

  • and astronomers have two basic ideas about how they form.

  • In one model, called hierarchical accretion,

  • objects start small and grow as they run into other stuff.

  • The other idea, known as gravitational instability,

  • suggests that full-sized planetesimals basically form all at once

  • as big clouds of gas and dust collapse.

  • New Horizons' results suggest this second one is probably the right answer,

  • at least for the Kuiper Belt.

  • That's because hierarchical accretion leads to more violent collisions,

  • not the slow, gentle impact that created Arrokoth.

  • Other New Horizons observations,

  • like the fact that the two lobes have the same composition,

  • support the idea that they formed from a gravitational instability.

  • After all, if they formed near each other, they'd both be made of the same stuff

  • and wouldn't have to pick up much speed to collide.

  • Conditions in the inner solar system may have been different during planet formation,

  • so it's not yet clear how broadly these conclusions apply,

  • but figuring it out for even the Kuiper Belt is a really big deal.

  • And that's just one example of what New Horizons has uncovered.

  • It also searched for rings, estimated Arrokoth's age,

  • and calculated how much gas might've been in the early Kuiper Belt.

  • So while it's likely that we'll never visit this tiny, freezing world again,

  • scientists now have enough data to explore its mysteries for years to come.

  • In the meantime, while we wait for the next set of results,

  • we have an odd, supergiant star to keep an eye on.

  • While astronomers are working on telling the story of our solar system,

  • there are lots of other stories waiting to be told.

  • Right now, I'm listening to There There by Tommy Orange which follows

  • 12 native characters leading up to the Big Oakland Powwow in California.

  • My favorite character is Orvil, who teaches himself

  • traditional dance through YouTube videos,

  • but so far I'm in love with all the characters, and I think you will be too.

  • And I haven't finished the story yet, so if you have, no spoilers in the comments, please!

  • You can find this audiobook on Audible, along with tons of other amazing stories.

  • Next up, I'm planning on listening to Never Home Alone by Rob Dunn

  • all about the critters living in your home with you.

  • So whether you're into literature, science and technology,

  • journalism or other kinds of storytelling, Audible has something for you.

  • An Audible membership includes one free audiobook a month

  • and 30% off all regularly priced audiobooks.

  • And Audible can help you reach lots of other goals, too,

  • like making better use of your commute or becoming a more open-minded person.

  • You can get your first audiobook for free if you try Audible for 30 days,

  • and you'll get two Audible Originals.

  • To get started, visit audible.com/scishowspace or textscishowspaceto 500 500.

  • [♪ OUTRO]

This episode is sponsored by Audible.

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ベテルギウスは薄暗いだけじゃない。貧弱なだけではない。 (Betelgeuse Isn’t Just Dim: It’s Lopsided | SciShow News)

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    林宜悉 に公開 2021 年 01 月 14 日
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