From thousands of galaxies, each with billions of stars.

何万光年という彼方にある

Imagine, you could take this kind of power, and use it to fire the biggest super-weapon in the universe.

何億という星々のエネルギーを集め

Imagine the damage you could do.

その力を使って

It turns out, you don't need to imagine it.

宇宙で最強の武器を作ったら

These exist, and they're called gamma ray bursts.

どうなるのか

But what are these cosmic snipers?

いや 想像しなくてもいい

And what happens if one takes a shot at Earth?

すでにある

To understand gamma ray bursts, we first have to understand gamma rays.

ガンマ線バーストだ

Gamma rays are electromagnetic radiation – waves which carry energy just like visible light.

もし宇宙のスナイパーが

Visible light is a tiny part of the electromagnetic spectrum: it's the part your eyes can see.

地球を撃ったらどうなるのか

At lower energies, there are radio waves, microwaves and infrared.

まずはガンマ線について説明しよう

And at higher energies: ultraviolet, x-rays and gamma rays.

ガンマ線は電磁放射線で

Gamma rays are incredibly powerful.

エネルギーを運んでいる

A single gamma ray photon, is more energetic than a million visible photons combined.

目に見える光も

Their high energy makes gamma rays a form of ionizing radiation.

そのような電磁波の一部だ

Meaning they are energetic enough, to break apart atomic bonds.

エネルギーが低いものに

This makes them dangerous to you and me.

マイクロ波や赤外線

Ionizing radiation disrupts the delicate biochemical machinery that keeps us alive,

高いものに 紫外線やX線

like a 9mm bullet through a clock.

ガンマ線がある

Fortunately, on Earth, the ozone layer blocks gamma rays. Filtering them out before they can harm us.

ガンマ線はとても強力だ

But if the atmosphere blocks gamma rays from space,

ガンマ線光子１個で

how were gamma ray bursts (or GRBs) from space ever discovered?

可視光光子100万個よりも強い

During the Cold War,

これにより電離放射線となっている

the USA sent up spy satellites, which could detect gamma rays from Soviet nuclear tests in space.

原子の結合を壊せるということだ

They didn't see any bombs, but they did observe faint bursts coming from space,

これは危険なことだ

lasting only a few seconds.

生物に必要な構造を壊してしまう

To date, this may be the only major scientific discovery made by spy satellites (that we know about anyway).

銃で撃つように

Astronomers use telescopes see different kinds of light to make their discoveries.

幸い 地球にはオゾン層があり

And these spy satellites gave them a new pair of eyes.

ガンマ線を防いでいる

They were a mystery for thirty years but eventually,

ではガンマ線バーストは

we discovered the source of a GRB: a galaxy six billion light years away.

どのように発見されたのだろうか

If a GRB can be seen from such a distance, then it must be incredibly energetic.

冷戦中 アメリカは衛星を使って

Releasing more energy in a second than the sun will, in its entire ten billion year lifetime.

ソ連の核実験を監視していた

Making GRBs, the brightest events in the universe.

核爆発による放射線はなかったが

So, where do they come from?

宇宙からの放射線があった

GRBs, accompany some of the most violent, cataclysmic deaths in the universe,

スパイによる唯一の科学的大発見だ

and the birth of black holes.

知られている限りで

There are two types of gamma ray bursts:

天文学者が向ける宇宙への視線に

short and long, and each has their own source.

新たな視点が加えられた

Long GRBs last about a minute, and scientist think they are produced by supernova:

30年謎だったが

when the core of a massive star collapses to become a black hole.

最終的に 60億光年先に

Short GRBs last a second, and are produced when two neutron stars in a binary merge.

ガンマ線の発生源を見つけた

Over millions of years, their orbits decay by emmiting gravitational waves.

距離から考えると

Once they are close enough to touch, they crash and splash into each other, forming a black hole.

驚くべきエネルギーだ

Both supernova and neutron star mergers the same thing:

１秒で 太陽一生分よりも多い

black holes, surrounded by a magnetized disc of gas left over from their parent stars.

エネルギーが出たことになる

In these environments, the rotation winds up the magnetic field, which funnels hot jets of particles,

宇宙で最も眩しい出来事だろう

traveling at nearly the speed of light.

それはなぜ起こるか

The gas in this funnel creates two tight jets of high energy gamma rays,

宇宙で最も破滅的な現象は

like a celestial laser gun.

新たな天体の誕生でもある

So unlike other cosmic explosions, which spread out and fade,

ガンマ線バーストは２種類あり

GRBs say focused, and can been seen from much further.

出所が異なる

Any more detail would require too much mathematics for a YouTube video.

長い方は超新星爆発によるものだ

The universe is full of these cosmic snipers, firing blindly and randomly into the dark,

結果 ブラックホールができる

and they're hitting us all the time.

短い方は２つの中性子星が

On average, we detect one per day. Fortunately, most are harmless.

合体する時に出る

All the bursts we have detected so far, originated outside the Milky Way,

何百万年か重力波を出し続けたあと

too far away to hurt us.

徐々に近づき

But a nearby GRB could be disastrous,

ぶつかってブラックホールができる

if one goes off within a few light years of us, it would totally cook the surface of the Earth.

両方とも同じものができる

Or at least, the half that's facing it.

周りには磁気を帯びた

But even a more distant GRB could still end life on Earth.

星の残骸のガスがあり

And it wouldn't need to score a head-shot to kill us.

それが回転して磁場を作ると

If originating from a few thousand light years away,

中心から熱い粒子が

it would be a hundred light years wide by the time it reaches us,

ほぼ光速で放出される

washing over the Solar System like a tidal wave.

噴き出る高エネルギーのガンマ線は

Again, the ozone layer protects us, but it's better equipped to handle the trickle of ultraviolet from the sun.

まるでレーザー銃だ

A gamma ray burst would overwhelm it, leaving us exposed to deadly solar radiation.

他の爆発では拡散するものが

Ozone takes years to replenish itself by natural processes,

集中して より遠くに届くようになる

which is more than enough time for the sun to burn the Earth sterile.

詳細は数学が必要なのでやめとこう

Or at least, to kill most complex life.

そんな光線がたくさん

In fact, this may have already happened.

闇の中を飛び交い

A GRB has been suggested as one possible cause of the Ordovician extinction 450 million years ago,

地球にも来ている

that eradicated almost 85% of all marine species.

１日に１回ほどだが

Although it's pretty much impossible to prove.

幸い ほとんどが無害だ

Gamma ray bursts could even be one reason we don't see life anywhere else in the universe.

どれも銀河の外から来ているため

They might be wiping clean huge chucks of it, on a regular basis.

危険はない

It's been suggested, that because of GRBs, only 10% of all galaxies might be hospitable to life,

しかし近ければ危険だ

similar to us.

数光年の距離なら

So, are they going to kill us?

地球は丸焦げだろう

Probably not.

少なくとも半分が

In a galaxy like ours, there may only be one GRB per millennia.

それより遠くても十分危険はある

And to harm us, they must be close and directed at us.

ヘッドショットではなくても

But since gamma rays travel at the speed of light, we won't know when it's headed our way until it arrives.

数千光年先からなら

So, there could already be a GRB on its way to kill us all, and we won't know it, until it hits us,

来る間にその幅が広がって

and we're dead.

太陽系全体を揺さぶるだろう

This video was sponsored by squarespace.com/nutshell

オゾン層は太陽から

Death from the sky could come around any second.

地球上の生物を守っているが

Maybe, even now!

それが壊された場合

So you don't have any time to waste.

太陽に焼かれることになる

Learning to set up a website, portfolio or blog is usually hard and time consuming.

オゾン層は再生に数年かかる

Not so with Squarespace though.

地球を焼くには十分な時間だ

They let you set up a page with easily understandable tools, very quickly,

複雑な生物は死ぬだろう

and without any knowledge of web design.

実際すでに起きたかも

You can use the code "NUTSHELL" to save 10% and support Kurzgesagt.

ガンマ線バーストが原因となって

Squarespace have been a great sponsor, so give them some love.

4.5億年前 オルドビス紀に

You can support us directly at Patreon or get Kurzgesagt merch here:

85％の海洋生物が絶滅した

it really helps.

という説が存在する

Over the next few months, we'd like to make more videos about cataclysmic destructive events,

宇宙人がいない理由はこれだろうか

because, honestly, it's a lot of fun to make these.

生物は消し去られ続けてきたのか

If you have any ideas about what kind of doomsday scenario you'd like to learn about,

だから 10％の銀河でしか

let us know in the comments.

生命は存在できないという説もある

And if you need to kill a little more time now, here are few related videos.

私たちはどうか

Or maybe...

たぶん大丈夫

NOW!

銀河内での発生は1000年に１回だし