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  • [♪ INTRO]

  • Astronomers are always finding weird stuff in the universe.

  • But sometimes, their discoveries are especially strangeand maybe a little spooky.

  • According to a paper published last week in Nature, astronomers have found a star about

  • 500 million light-years away that just won't quit.

  • It appears to have died and come back to life multiple times, almost like… a zombie star.

  • When really large stars run out of fuel, they can explode in gigantic,

  • beautiful explosions called supernova.

  • And scientists can describe them using graphs called light curves.

  • A light curve shows you how bright an object is over some amount of time.

  • For a supernova, the curve should look really bright at first, because it's exploding,

  • and then it should taper off as everything disperses and cools.

  • Normally, a supernova doesn't stay bright for long: only about 100 days.

  • And it only happens once because, well, the star is dead after that.

  • But the light curve for this new supernova, called iPTF14hls, which is so easy to remember,

  • has all kinds of fun bumps in it, like it's pulsing.

  • And even though we discovered it in 2014, it's still really bright three years later.

  • It's also way brighter than your average, garden-variety supernova!

  • So far, we've recorded it being almost three and a half billion times as bright as the Sun,

  • while regular supernova usually aren't more than 500 million times brighter.

  • But the weirdest part is that this object might have exploded before!

  • After seeing how strange it was, the team searched through previous research for

  • similar phenomena, and they found an explosion recorded in the same spot in 1954!

  • So, it seems like the star died about 60 years ago,

  • but then made a comeback and exploded again.

  • Right now, there isn't a full explanation for its behavior,

  • but part of it may have to do with its mass.

  • The team calculated that, before it exploded,

  • the star was at least 50 times the mass of the Sun, and probably a lot bigger than it.

  • And even though we've found thousands of supernova,

  • we haven't yet seen a star that big die, so it could work differently than expected.

  • Another, even cooler option is that this may be

  • the first recorded pulsational pair-instability supernova, or PPISN.

  • This is something scientists have modeled, but never observed in real life.

  • The idea is that, a star that's massive and hot enough might start manufacturing pairs

  • of electrons and their antimatter opposite: positively-charged particles called positrons.

  • And creating these pairs might drive the supernova's weird pulses.

  • Making them uses up energy that the star would normally use to stop itself from collapsing.

  • But since it is used up, the star contracts.

  • That causes more elements to burn in the star's core, which gives off a bunch of extra light,

  • until the star eventually cools down and expands.

  • And then the cycle begins again.

  • So, more pulses.

  • Still, the team also doesn't think a PPISN could fully explain what's happening,

  • because we think those supernova get rid of most of their hydrogen early on,

  • while this one has lots of hydrogen leftover.

  • Plus, in this recent explosion, the mystery supernova has about

  • ten times more energy than what PPISNs should.

  • So it remains under close observation!

  • This week, astronomers reported another mystery in the journal Nature,

  • but this time, it was about Pluto, and they've solved it!

  • As it turns out, Pluto is super cold, which believe it or not, is unexpected.

  • Okay, we already knew it must be kinda cold,

  • because it's tiny and billions of kilometers from the Sun.

  • But after New Horizons flew by in 2015,

  • we found that it's about 40 degrees Celsius cooler than we thought.

  • According to new research, that's probably because it has a unique atmosphere.

  • Studying an object's atmosphere is crucial to understanding its temperature,

  • because atmospheres are normally fluffy, regulating planetary blankets.

  • On most planets, it's the gases in the atmosphere that do the regulating,

  • like how carbon dioxide influences Earth's temperature.

  • But on Pluto, it's not the gases: It's haze, or something a little like smog.

  • From previous research, we already knew that Pluto has a somewhat hazy atmosphere,

  • because light passing close to its surface was dimmer than we'd expect.

  • New Horizons confirmed that, but it also found that the hazes are more abundant

  • and stretch higher than we thought: about 700 kilometers above the surface.

  • Still, that didn't explain why Pluto is so cold.

  • But before we could learn more, New Horizons flew off farther into the Kuiper Belt,

  • so we couldn't gather the data to explore this temperature problem.

  • And that's where modeling stepped in.

  • A team of scientists built a new and improved model of Pluto's atmosphere, and they found that,

  • if they set it up so that hazes were the main thing controlling Pluto's temperature,

  • the model matched the New Horizons data!

  • In other words, Pluto's atmospheric hazes are mainly what's making it so cold,

  • not its gases.

  • That haze is likely made of lots of bigger hydrocarbons, which formed when light

  • drove certain chemical reactions, a lot like how smog can form on Earth.

  • Those molecules are really great at sucking up energy,

  • but they're also great at radiating it away.

  • The hydrocarbons distribute the heat among themselves really rapidly,

  • then force a lot of that heat into the upper atmosphere, where it spreads into space.

  • And that leaves Pluto extra chilly.

  • As far as we know, the only place in the solar system

  • with a temperature controlled by hazes like this is Pluto!

  • And since hazes seem to play an important role in the atmosphere of some exoplanets,

  • this research might also help us explore worlds farther away.

  • That little dwarf planet just keeps impressing us!

  • So this week, all kinds of expectations are being thrown overboard in the solar system!

  • And I'm sure that is not the last time I'll say that.

  • Thanks for watching this episode of SciShow Space!

  • If you'd like to keep up with the latest news from around the universe,

  • you can go to youtube.com/scishowspace and subscribe.

  • [♪ OUTRO]

[♪ INTRO]

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ただ死なないゾンビスター (A Zombie Star That Just Won't Die)

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    林宜悉 に公開 2021 年 01 月 14 日
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