It will probably be a red dwarf, a tiny kind of star,

宇宙は闇に包まれる

that's also one of our best bets to find alien life,

その星はおそらく赤色矮星で

and might be the last home of Humanity before the universe becomes uninhabitable,

その特徴から言って

so what do we know about them, and why are they our last hope?

人類の最後の住処となる場所だ

At least 70% of stars in the universe are red dwarfs.

なぜこの星が人類最後の希望なのか

They are the tiniest stars out there, with only about 7 to 50% of the mass of our sun,

宇宙にある恒星の70％は赤色矮星だ

not that much bigger than our planet, Juptier, which is still huge, though.

小さな星であり

They are also very dim.

質量は太陽の7～50％ほど

It's impossible to see them with the naked eye.

木星よりは大きい

You've never seen one in the night sky.

大きいが とても暗い

Even with all our technology,

夜空に肉眼で見ることはできない

we can only clearly observe red dwarfs in our neighborhood.

現代技術なら近くのものが観測でき

Approximately 20 of the 30 stars close to Earth are red dwarfs.

20個ほどが見つかっている

Like all stars, red dwarfs fuse hydrogen into helium,

赤色矮星も他の星同様 核融合を行う

but while more massive stars accumulate all the fused helium in their cores,

大きな星は核で核融合を行うが

red dwarfs stay convective, meaning that the helium and hydrogen constantly mix,

赤色矮星は流動的で

so they use up their fuel incredibly slowly before they are extinguished.

中が混じり合っている

Red dwarfs burn so slowly

そして燃料の消費速度がとても遅い

that their average lifespan is between one and ten trillion years;

ゆっくり燃えるため

by comparison, the Sun will survive for another five billion years.

平均寿命は1～10兆年まで及んでいる

Because the universe is only 13.75 billion years old,

太陽の寿命は残り50億年だ

not a single red dwarf has reached later development stages.

宇宙の年齢は137億年だから

Every single one of the trillions that exist is still a baby.

死んだ赤色矮星はいない

Speaking of babies, the smallest star in the entire universe

赤色矮星はみんなまだ赤ちゃんだ

is also a red dwarf because small red dwarfs are right on the verge of being a star at all.

また宇宙で最も小さな恒星でもある

Just a tiny bit less hydrogen, and they are mere brown dwarfs,

恒星になれる最小の大きさだからだ

failed stars that cannot sustain a fusion reaction for long,

これ以下だと褐色矮星になる

so what about aliens or a new home for Humanity?

核融合できないただの星だ

Since our sun will die one day, we'll eventually need to look for a new home,

生物にとってはどんな場所だろうか

and where there are habitable planets, there might also be aliens.

太陽が死んだら 新しい家が必要だ

The Kepler space observatory found that at least half of all red dwarfs host

快適な場所なら 宇宙人がいるかも

rock planets between half and four times the mass of our Earth.

観測では 赤色矮星の半数に

Many of them are in the habitable zone, the area around a star where water can be liquid,

地球の半分以下の小さい惑星がある

but since red dwarfs burn at relatively cold temperatures,

水が液体で存在できる

a planet would need to be really close to be hospitable,

良い距離のものもある

probably as close as Mercury to our Sun or even closer

赤色矮星は温度が低いため

which brings with it all kinds of problems.

その距離は短くなる

For example, a planet this close to a star would probably be tidally locked,

太陽と水星の距離くらいだろう

meaning the same side would always face it.

だがこれが問題をもたらす

This side would be incredibly hot, while the shadow side would be frozen

近すぎるために向きが固定され

which makes it hard for life to develop;

常に同じ面が向く

although, a planet with a big enough ocean might be able to distribute the star's energy

表はとても熱く

and create some kind of stability.

裏は凍りついて住みにくいだろう

All the gravitational forces of the red dwarf could squeeze the planet

惑星に大きな海があれば

and heat it up so much that it might lose all its water over time.

熱が分散されて安定するが

These planets could end up like Venus, a hot burning hell.

強い重力によって惑星は角張り

Another problem is that many red dwarfs vary in their energy output.

水も蒸発してなくなるかもしれない

They can be covered in star spots that condemn their emitted light by up to 40% for months

そして金星のような灼熱地獄になる

which would cause oceans on planets to freeze over;

出るエネルギーの安定性も問題だ

at other times, they can emit powerful solar flares,

黒点が現れ 光を40％に弱め続ければ

sudden outbursts of energy incredibly powerful.

惑星の海は凍ってしまう

These red dwarfs could double their brightness in minutes

また時には強力なフレアが

which could strip away sizable portions of a planet's atmosphere and burn it,

突然火を噴くこともある

rendering it sterile;

数分で倍の明るさになり

on the other hand, their extremely long life span is a big plus.

惑星の大気の大部分を

A red dwarf with just moderate levels of activity

燃やし尽くしてしまう

could be an amazing place for a planet that hosts life.

それでも寿命の長さは利点だ

Life on Earth has existed for about four billion years,

活動が安定していれば

and we have about a billion years left before the Sun becomes so hot

移り住むにはとても良い

that complex life on Earth will become impossible.

生命は40億年存在してきた

We will either die out or leave Earth and look for a new home.

だが太陽は10億年後には

We could build a civilization for potentially trillions of years

熱くなりすぎている

around a red dwarf with the right conditions.

そうなる前に引っ越しが必要だ

About 5% of the red dwarfs in the Milky Way may host habitable, roughly Earth-sized planets.

良い条件の星があれば

That would be more than four billion in total,

数兆年住むことができる

but life may not even need a planet like Earth.

赤色矮星の５％には

Candidates for life around a red dwarf may be the moons of gas giants,

地球に似た惑星が存在し

also called Super Earths, really massive rocky planets.

全部で40億個ある

All alone, there are an estimated 60 billion potentially habitable planets

地球に似てはいなくても

around red dwarfs, and that's in the Milky Way alone,

巨大ガス惑星の衛星や

so red dwarfs might become really important for our survival in the future,

巨大な岩 スーパーアースがある

but everything has to die at some point, even red dwarfs.

これらの星が600億個

When in trillions of years the life of the last red dwarf in the universe is about to end,

赤色矮星の周りに存在する

it will not be a very spectacular event.

この天の川銀河だけで

As its hydrogen runs out, it shrinks becoming a blue dwarf, burning out completely.

赤色矮星は将来 重要になるだろう

After its fuel is spent, it's transformed into a white dwarf,

しかし赤色矮星もいつかは死ぬ

an object about as small as Earth, packed very densely,

数兆年後 赤色矮星が死ぬ時が来るが

and made of degenerate gasses, mostly of Helium-4 nuclei.

特に大したことは起きない

Having no more source of energy, it will cool extremely slowly

縮んで青色矮星になり さらに燃える

over trillions of years until it becomes its final form: a cold black dwarf.

燃え尽きると白色矮星になる

White and black dwarfs are so fascinating that they deserve their own video;

地球大で密度が高く

anyway, it's going to be a long time before the last stars in the universe vanish.

ほとんどヘリウム４でできた物体だ

It's kind of uplifting to know that, if Humanity succeeds in venturing into Space,

もうエネルギー源はなく

we have plenty of time before the universe turns out the lights.

数兆年かけて冷えて

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最後の形 黒色矮星になる

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これらは別の動画で説明しよう

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最後の星が死ぬまで長い時間がある