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

紅矮星這種小型的恆星或許是我們

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

得去孤注一擲去尋找外星生命得場所， 或是成為人類最後的安棲之所

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

我們對紅矮星了解多少， 又為何它們是我們的最後希望？

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

在宇宙中的恆星至少有70％是紅矮星

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

它們是宇宙中最小的恆星，值量僅有太陽的7%到50%。

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

比起木星差不了多少，不過依然很大。

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

它們相當黯淡。

They are also very dim.

我們很難用肉眼觀察到它

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

當你在夜晚注視天空時，你絕對看不到它們

You've never seen one in the night sky.

即使使用現在的技術，我們也只能清晰地觀察到鄰近我們的紅矮星

Even with all our technology,

鄰近地球的紅矮星大約有20~30顆

we can only clearly observe red dwarfs in our neighborhood.

如同所有的恆星一般， 紅矮星把氫核融合成氦

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

其他質量較重的恆星， 會將融合成的氦聚集到核心之中。

Like all stars, red dwarfs fuse hydrogen into helium,

紅矮星則是將氦分散到各處，所以紅矮 星中的氫和氦持續不斷的混合一起。

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

所以在它們死亡之前，它們使用燃料的速度出乎意料的慢

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

紅矮星燃燒得很慢，紅矮星的生命週期有一兆到十兆年不等。

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

相較之下，我們的太陽只能再活五十億年

Red dwarfs burn so slowly

因為宇宙只有一百三十七億多歲

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

尚未有任何紅矮星進入下一個發展階段

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

每一個已存在一兆年的紅矮星 都還算是個小寶寶

Because the universe is only 13.75 billion years old,

說到寶寶，在宇宙中

not a single red dwarf has reached later development stages.

全宇宙中最小的恆星，紅矮星剛好符合恆星的最低標準

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

如果氫的質量再少一些，它將只是棕矮星

Speaking of babies, the smallest star in the entire universe

無法持續進行融合反應，無法成為恆星

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

這和外星人和人類新家有何關係？

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

既然太陽終將毀滅，人類將來勢必要 找新家

failed stars that cannot sustain a fusion reaction for long,

宜居的行星當然也有可能存在外星人

so what about aliens or a new home for Humanity?

克卜勒天文台發現半數以上的紅矮星系

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

都有岩質行星存在，質量從地球的一半 到四倍不等

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

多數多處於可居範圍內，在此範圍內， 水可以保持在液態

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

但因為紅矮星以較低溫度運作

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

行星必須更靠近紅矮星才適宜居住

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

或許要像水星靠太陽那麼近才可以

but since red dwarfs burn at relatively cold temperatures,

然而所有麻煩都因此而生。舉例來說 靠恆星這麼近的行星常常被「潮汐鎖定」(同步自轉)

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

被潮汐鎖定的行星永遠只會用同一面 面對恆星

probably as close as Mercury to our Sun or even closer

向光面會熱到不得了， 背光面則會冷到凍結，大大不利生命

which brings with it all kinds of problems.

如果該行星有夠大的海洋，或許可以均勻分散紅矮星的能量，帶來部分的穩定。

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

行星被紅矮星重力不斷擠壓，並過度加熱之下，

meaning the same side would always face it.

隨時間過去，可能會喪失所有水分。

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

這些行星最終可能會像金星一般， 變成一個灼熱的煉獄。

which makes it hard for life to develop;

有些紅矮星的能量輸出變換不定， 則是另一個大麻煩。

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

紅矮星有時會被星斑覆蓋，將使發出的 光芒減少最高達40%，為時數月

and create some kind of stability.

這將使該行星的海洋為之凍結

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

有時紅矮星則散發極有威力的閃焰，這種突然暴發的能量威力無窮。

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

此時的紅矮星亮度會在數分鐘內加倍，

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

這會奪走行星大部分的氣體，並燒了它們

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

另一方面，它們極長的壽命是一大優勢

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

一個處於平穩狀態的紅矮星 就可使行星成為一個承載生命神奇的地方

which would cause oceans on planets to freeze over;

地球上的生命已經存在了40億年

at other times, they can emit powerful solar flares,

而且，我們有大約十億年的時間離開 太陽變得太熱，地球上的複雜的生命

sudden outbursts of energy incredibly powerful.

將不復存在

These red dwarfs could double their brightness in minutes

我們要麼死了，要麼離開地球尋找一個新的家

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

我們可以在數萬億年中建造文明 生活在紅矮星附近

rendering it sterile;

銀河系中約有5％的紅矮星可遷移居住 大致上與地球大小相差無幾

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

總共可能超過40億個

A red dwarf with just moderate levels of activity

但生態可能不會像地球一樣

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

圍繞紅矮星生活的也可能有大氣衛星 (moons of Gas Giants)也稱為超級地球衛星

Life on Earth has existed for about four billion years,

真正的大型岩石行星。

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

獨自一人 周圍的紅矮星估計還有60億潛在適合居住的行星

that complex life on Earth will become impossible.

而且，這僅僅是在銀河系

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

因此，紅矮星可能成為我們未來的生存非常重要的關鍵

We could build a civilization for potentially trillions of years

但在某個時候一切都會死亡，即使是紅矮星

around a red dwarf with the right conditions.

當在萬億年最後一個紅矮星的生命即將結束時 它絕對不會是一個非常壯觀的事情

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

當它的氫耗盡時，它會縮小成為藍矮星，最後整顆燃燒

That would be more than four billion in total,

當燃燒完畢時，它變成了一個白矮星，一個如同地球大小的星球

but life may not even need a planet like Earth.

構造非常密集，並主要由氦原子核組成

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

沒有更多得能量來源 它會在萬億年間緩慢的冷卻

also called Super Earths, really massive rocky planets.

直到它成為其最終形式：一個寒冷的黑矮星

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

白與黑矮星是如此令人著迷，他們應該擁有自己的影片

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

反正......在宇宙消失前，還有許多時間

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

如果人類成功地進軍太空，這會使任何人振奮

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

在宇宙熄滅之前，我們還有足夠的時間

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

你對Patreon.com支持是我們製作影片的動力，如果您想幫助我們製作更多影片

it will not be a very spectacular event.

我們非常感謝您的支持 ; )

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

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

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

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

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

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.

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.

Our videos are made thanks to your support on Patreon.com.

If you want to help us make more of them, we really appreciate your support!

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