galaxies. We have no real metaphor for their power  – if the sun were to magically go supernova it  

銀河を凌駕するほどの エネルギーを放つ

would feel like you were being hit by the energy  of a nuclear explosion, every second. For weeks. 

比喩で表せぬほど強力で もし太陽が超新星となれば

While supernovae are the engines of creation,  forging the elements that enable life, they also  

核爆発に毎秒 襲われている感じだろう

burn sterile whole regions of galaxies.  So what would happen if one hit earth?

何週間もだ

There are roughly speaking two ways to  make a supernova. Either the core of a  

超新星は生命につながる物質を 創造しうる一方

massive star implodes, or, less common, a  white dwarf gains mass to the point where  

銀河の全領域を不毛とすることもある

it ignites explosive nuclear fusion. The  outcome is the same: a supernova explosion. 

もし地球が襲われたら どうなるだろうか

If we think of an explosion on earth, we  think of something that happens fast and ends. 

超新星を発生させるには 2つの方法がある

But a supernova is more like a volcanic  eruption followed by a tsunami. At first  

重い恒星の崩壊か

there is a colorful ball of hot, expanding gas,  creating a spectacular cloud that will shine for  

珍しくは、白色矮星が質量を得て 爆発に至るかだ

about a month – but then it doesn’t stop. Hot  and dangerous gas rushes outward at speeds of  

結果は同じことで 超新星爆発がおきる

10,000 km/s through the near vacuum of space,  sweeping up the sparse gas of the galaxy.  

「爆発」を想像すると 瞬時に終わる印象があるが

This wall of gas expands for tens of thousands  of years and will eventually span up to dozens  

しかし超新星は 噴火と津波のようなものだ

of light-years until it finally cools off, and  disperses its substance back into the galaxy. 

まずきれいで熱い球から ガスが膨張し

So what if this star tsunami hits us? Well,  the damage depends on how far away it is.

壮大な雲を作り、ひと月ほど輝くが それで終わりではない

Stage 1: Thousands of Light Years away 

熱くて危険なガスが 秒速1万kmの速さで突き進み

Humans have witnessed dozens of supernovae but  all of them were thousands of lightyears away.  

銀河のガスを一掃する

They appeared as new stars, some outshining  the moon, twinkling for a few weeks and  

このガスの壁は何万年もかけて膨張し

disappearing. Aside from looking very pretty  at this distance they don’t do much to us.

最終的には何十光年にも及び 熱も冷めて

Stage 2: 300 Light Years away Things begin to get a tiny bit  

物質を銀河に撒き散らすのだ

icky once a supernova occurs around 300  lightyears away. We can expect one this  

この津波が我々を襲ったらどうなるだろう

close to us every few million years:  a single star giving the night sky  

その被害は 距離によって異なる

an eerie glow like twilight. And while this  is far and dim enough not to do harm to us,  

ステージ1：数千光年の彼方

they can affect the earth. At these distances  it is like being hit by the last weak waves  

人類は何度も超新星を見てきたが みな数千年の彼方だった

of the star tsunami. Not strong enough  to do real damage but still noticeable. 

新しい星として現れ、あるものは月を凌駕し 数週間瞬いて消える

In fact, we know that over the past 10 million  years multiple supernovae have struck Earth from  

見た目はきれいだが 我々に影響は与えない

these distances because we can find radioactive  isotopes of iron deep in the rocks and sediments  

ステージ2：300光年の彼方

at the bottom of the ocean. Amazingly, these  supernovae around the solar system have cleared a  

300光年先の超新星は 少々気味の悪さを覚える

1000 light-year wide pocket of space that is  called the 'Local Bubble'. They blew away the  

闇夜に不気味に光る 薄明かりの星が

interstellar gas and dust, creating a lumpy wall  of gas that is now a cradle for star formation.

数百万年毎に 発生すると考えられている

Stage 3: 150 Light Years Away Once a supernova happens much closer  

この距離では被害に合うことはないが 地球には影響がある

than 300 light-years, we’re approaching  the zone where it does real damage. 

この距離だと弱々しい星の津波に 襲われるようなものだ

Stars have extremely powerful magnetic fields.  When they die, the tsunami of dead star actually  

被害を与えるほどではないが とは言え気づく

retains a lot of this magnetic energy, woven  through the shockwave that expands outwards.  

実際、過去にも複数の超新星が 地球に到達したとみられており

In this highly magnetized cloud,  we get conditions like in a huge  

海底の岩などから特定の鉄の 放射性同位体を見つけられる

particle accelerator that is accelerating  charged particles like protons, nuclei,  

驚くべきことに、太陽系近くの超新星は 千光年の空間を一掃し局所泡を作った

and electrons to immense speeds. Which means we  have an expanding cloud that is shooting deadly  

星間ガスやチリを吹き飛ばし 今や星形成のゆりかごとなっているのだ

radiation in all directions, long after the bright  light from the initial explosion has faded away. 

ステージ3：150光年の彼方

If a supernova happens too close by, waves  of these ‘cosmic rays’ will wash over the  

300光年よりも近づくと 実際に被害を受け始める

solar system for thousands of years. While  we’re mostly protected on earth’s surface  

恒星は非常に強力な地場を持っている

by the atmosphere and ozone layer, the influx  of extra radiation will still increase cancer  

星が死んだあとの津波には 多くの磁力が残こされ

and mutation rates. Not enough to cause a  mass extinction but it will be noticeable. 

衝撃波として外側に広がる

Spaceflight would become  impossible in the solar system,  

この強い磁場の雲の中では 巨大な粒子加速器が形成され

as astronauts would not survive  the waves of radiation for long.  

陽子や原子などの荷電粒子を ものすごいスピードに加速する

We don’t know exactly how bad this would  be, but a supernova that is close enough may  

つまり爆発の閃光が消えたあとも

trap our species on earth for generations, maybe  thousands of years. It only gets worse from here.

致命的な放射線を放つ雲が 広がっているのだ

Stage 4: Closer than 100 light years Within 100 light years, things get bad,  

もし超新星がすぐ近くで起きれば この津波が何千年も押し寄せることになる

as a supernova disrupts our climate in  ways that we don't fully understand yet.  

地球は大気とオゾン層で守られているが

There are a few unpleasant things  happening all one after another: 

余計な放射線は 癌などの発生率を高めるだろう

First, the high energy photons arrive from the  explosion, followed by many decades of radiation  

大量絶滅は起きないが 目立つ変化がおきる

from the radioactive tsunami, both of which  seriously damage the ozone layer, earth’s shield  

宇宙飛行士もこれに耐えることができないので 宇宙飛行は不可能になる

against harmful radiation. The ozone layer absorbs  ultraviolet radiation by breaking apart ozone, O3,  

どの程度酷いかはわからないが 近すぎる超新星は

into O2 and a free oxygen atom, which later  reforms back into another ozone molecule.  

我々を何千年も 地球に閉じ込めるかもしれない

But the supernova radiation breaks up Nitrogen  molecules that gobble up the free oxygen,  

だが、更に悪くなる

breaking the cycle and depleting the ozone  layer quickly: Without a radiation shield  

ステージ4：100光年より近い

everybody living on the surface is exposed  to very high levels of UV radiation from our  

100光年以内では さらに悪化し

sun – cancer rates would skyrocket and just going  outside during the day could be life threatening. 

全てを理解してはいないが 気候にも変化があるだろう

The extra radiation would also kill a lot, if not  most of the plankton in the oceans that live near  

次から次へと不愉快なことがおきてしまう

the surface and are the basis for the marine  food chains – leading to a mass extinction. 

まず高エネルギーとなった光子が飛来し 放射線が何十年にもわたって降り注ぎ

Worse still supernova radiation would ionize gas  in the atmosphere, which means that it would punch  

地球の盾であるオゾン層に 深刻なダメージを与えるだろう

through molecules and knock electrons off nuclei,  leaving them charged. These charged nuclei then  

オゾンはO3からO2と遊離酸素に分解し それが再びO3となる時に

act as seeds for water vapor to gather and form  massive global clouds. In the worst case they  

紫外線を吸収している

would reflect enough sunlight to trigger an ice  age. In fact, it's thought that the ice age 2.5  

だが放射線は窒素を分解し それが酸素を吸収するので

million years ago was caused by a supernova. Some  scientists even think that a supernova about 60  

オゾン層が急速に破壊されてしまう

light years away might have been the cause for the  Devonian mass extinction 350 million years ago.

オゾン層がなければ地表に住む全てのものが 太陽からの高い紫外線を受け

But wait, there is more. The electrons punched  free by the radiation, form enormous electric  

癌の発生率は急上昇し 日中に外へ出ることは致命的になる

avalanches – or in other words: lightning. Earth  is hit by some of the worst thunderstorms in  

余計な放射線は海洋食物連鎖の 基礎であり海面近くに住む

millions of years. The intense lightning causes  global wildfires that consume forests and crops,  

海洋性プランクトンをも ほとんど死滅させてしまう

devastate cities, disrupt our electrical  grids and global supply chain. All while  

放射線は大気中の気体を電離する

a decimated ozone layer leaks deadly radiation. While in the past, the ecosystem may have bounced  

つまり原子から電子を叩き落とし 帯電させてしまう

back from a nearby supernova after a few thousand  or million years, there’s no guarantee modern  

この帯電した原子は水蒸気の元となり 巨大な雲を形成する

civilization can take a hit of this magnitude.  Food shortages, skyrocketing prices, and wars,  

最悪の場合、氷河期になるほど 太陽を遮ぎるだろう

as nations struggle to not be consumed by chaos. So a supernova this close would at the very least  

実際250万年前の氷河期は 超新星によると考えられており

do significant damage for hundreds or thousands  of years, if not end our modern civilization, and  

3億5千年前の デボン紀の大量絶滅さえ

with it millions or even billions of lives. Still,  humanity would likely survive and could recover.

60光年先の超新星が原因だと 考えている学者もいる

Stage 5: Closer than 25 light years A supernova closer than 25 light years  

おっと まだある

means that we’re in its ‘kill radius’ where  a mass extinction is all but guaranteed.  

放射線によって投げ出された電子は 膨大な電流の滝、つまり稲妻を発生させる

Probably about half of the ozone layer would  be destroyed, and massive climatic disruption  

最悪の場合数百万年は 雷に襲われるだろう

on a scale we have never witnessed would ravage  earth. Entire ecosystems would swiftly be wiped  

強烈な雷は森林や農作物を焼き尽くし

out by radiation, as global wildfires envelop the  planet. All the things described before happen,  

都市を荒廃させ 電力網やサプライチェーンを破壊する

but way more intensely and much faster. A few  people might survive for years in bunkers,  

これらが行われている間 致死の放射線も到達している

if they have food supplies, but the world  they return to will be devastated and  

過去にはこの被害からの回復が 長年かけて行われたのかも知れないが

hostile to life for hundreds of thousands of  years. Human extinction is extremely likely.

現代文明がこの規模の被害に 耐えられる保証はない

Final stage: 4 light years Being any closer to a supernova is very  

食糧不足、物価高騰、戦争など 各国が混沌に飲まれまいと必死になるだろう

unlikely because space is big. But the effects  would be extreme. Even from 4 light years away,  

これほど近い超新星は 現代文明を終わらせないまでも

the distance to Alpha Centauri, a supernova would  be almost as bright as the sun in the sky. While  

数千年にわたり 何十億という命を奪うかもしれない

casting two shadows could be fun for a few hours,  within days the earth’s surface gets as hot as a  

だが、人類は生き延び 復興するだろう

sauna, baking the surface for weeks until the  explosion fades. The surface of earth burns,  

ステージ5：25光年より近い

scoured of life. Even the oceans aren't  safe: the massive amount of radiation  

この距離は我々が 死の半径にいることを意味し

that follows burns away the ozone layer,  killing everything that sees sunlight. 

大量絶滅がほぼ確実となる

It would be the largest extinction event in  history, reducing life to a few survivors  

オゾン層の半分が破壊され

in the deep sea and critters in the deep  soil. Life basically has to start over.

いままでなかった規模の 気候変動が地球を襲うだろう

Conclusion: How worried do you need to be? So should you worry? No! Fortunately,  

地球規模の火災が星を包み 生態系全体が放射線によって破壊される

there are only a handful of stars that may explode  within 1000 lightyears of earth and none are close  

今まで述べたようなことが より激しく、より急速におきる

enough to be a serious threat. Even better, these  stars will probably not go supernova for many  

食料さえあれば数人は 生存するかもしれないが

millions of years. So you are safe. But there’s  no guarantee for the far future. As stars orbit  

彼らの世界は何十万年も 生命にとって過酷な土地になる

the galaxy, our descendants may find themselves  dangerously close to a supernova – but by then  

人類が絶滅する可能性は 極めて高い

a far more advanced and wiser humanity will  hopefully be able to just move out of the way. 

最終ステージ：4光年先

In any case, you can sleep well  tonight under the beautiful night sky.

宇宙は広いので、これ以上近くで 超新星が発生する可能性は低い

And if you dream about understanding the physics  behind this video and others–we’ve created a  

だが効果のほどは究極だ

series of lessons to build your understanding  of fundamental science. Made in collaboration  

ケンタウルス座α星と同じ4光年先でさえ 太陽と同じ明るさになる

with our friends at Brilliant, these lessons dive  deeper into topics from our most popular videos,  

数時間なら2つの影を楽しめるが 数日で地球はサウナのように熱く

including things like cosmology,  biology, and even climate science.

何週間も地表を焼くことになる

Brilliant is an interactive learning  tool that makes science accessible with  

地表は焼け野原になり 生命は失われる

a hands-on approach. Because we know that to  really learn something, you’ve got to do it.  

海も安全じゃない

Think of each lesson as a one-on-one  tutoring version of a Kurzgesagt video.

膨大な放射線がオゾン層を焼き払い 太陽光を受ける全ての生物は死滅する

In our latest lesson, you’ll journey  further into the conditions that can  

史上最大の大量絶滅となり 深海や地中深くの僅かな生物しか生き残れない

trigger a supernova and how to determine  the impact of one on a planet like ours.

生命は最初からのやり直しになる

Brilliant has thousands of lessons to explore—from  math-based topics like algebra and probability to  

結論：心配する必要はあるか

the concepts behind machine learning and quantum  computing. And with new lessons added each month,  

恐れるべきだろうか 答えはノーだ

including ones from Kurzgesagt, you’ll  always find something fascinating to learn.

幸い、千光年以内に 爆発しうる星はわずかで

To get hands-on with Kurzgesagt lessons now, go  to Brilliant.org/nutshell and sign up for free.  

脅威となりえる星は近くにない

And with a free trial of Brilliant Premium,  you can explore everything Brilliant has to  

更には、これらの星も数百万年は 超新星とならないだろう

offer. There’s even an extra perk for Kurzgesagt  viewers: the first 200 people to use the link  

つまり君は安全だ

get 20% off their annual membership, which  unlocks all of Brilliant’s courses in math,  

だが遠い将来の保証はない

science, and computer science. We love to go above and beyond with  

銀河を巡る星々は 我々の子孫にとって危険な存在かもしれない

our research –Brilliant will be the catalyst  to expand the limits of your knowledge.

だがその時は遥かに賢明な人類が 超新星を避けて通れるようになっているかもしれない