Name: 宇宙最後の星-赤い小人の説明 (The Last Star in the Universe – Red Dwarfs Explained)
Uploaded: 2021-01-14T06:25:45.000Z
Duration: 5 min 51 s

One day, the last star will die, and the universe will turn dark forever.

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

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

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

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.

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

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.

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,

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

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;

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,

not a single red dwarf has reached later development stages.

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

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,

so what about aliens or a new home for Humanity?

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.

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,

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

probably as close as Mercury to our Sun or even closer

which brings with it all kinds of problems.

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.

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

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

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

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

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.

These red dwarfs could double their brightness in minutes

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

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

A red dwarf with just moderate levels of activity

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

Life on Earth has existed for about four billion years,

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

that complex life on Earth will become impossible.

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

We could build a civilization for potentially trillions of years

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.

That would be more than four billion in total,

but life may not even need a planet like Earth.

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

also called Super Earths, really massive rocky planets.

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

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

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.

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

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.

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.

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

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,

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

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これらは別の動画で説明しよう

最後の星が死ぬまで長い時間がある