to gamma-ray bursts and supernovae that could exterminate life on Earth,

到可以讓地球上所有生命滅絕的

outer space has no shortage of forces that could wreak havoc on our tiny planet.

伽瑪射線暴和超級新星，

But there's something in space

外太空一點也不缺

that seems more terrifying than any of these –

可以在我們的小小星球上 造成大浩劫的力量。

something that wipes out everything it comes near.

但在太空中，有樣東西

Could the Earth be swallowed by a black hole?

似乎比上述的還要更駭人——

A black hole is an object so dense

任何東西只要靠近它 就會被徹底消滅。

that space and time around it are inescapably modified,

地球有沒有可能會被黑洞給吞噬？

warped into an infinite sink.

黑洞是密度超高的物體，

Nothing, not even light, can move fast enough

高到它周圍的空間和時間 都無法避免地被改變，

to escape a black hole's gravitational pull

扭曲成了無限大的槽。

once it passes a certain boundary,

即使是光也不夠快，

known as the event horizon.

無法逃離黑洞的引力牽引，

Thus, a black hole is like a cosmic vacuum cleaner with infinite capacity,

一旦它超過了某條界線，

gobbling up everything in its path, and letting nothing out.

也就是所謂的事件視界， 就無法脫離了。

To determine whether a black hole could swallow the Earth,

因此，黑洞是個容量 無限大的宇宙吸塵器，

we first have to figure out where they are.

狼吞虎咽它經過的一切， 什麼都不放過。

But since they don't emit light, how's that possible?

若要判斷一個黑洞 是否會把地球吞噬，

Fortunately, we're able to observe their effect on the space around them.

我們先要找到黑洞在哪裡。

When matter approaches a black hole,

但它們不會散發光線， 怎麼可能找到它們？

the immense gravitational field accelerates it to high speed.

幸運的是，我們可以觀察 它們對於周圍空間的影響。

This emits an enormous amount of light.

當物質靠近一個黑洞時，

And for objects too far away to be sucked in,

非常大的重力場會讓它加速 到極高的速度。

the massive gravitational force still affects their orbits.

這樣就會放射出大量的光。

If we observe several stars orbiting around an apparently empty point,

至於太遠而不會被吸進去的物體，

a black hole could be leading the dance.

極大的引力仍然會影響它們的軌道。

Similarly, light that passes close enough to an event horizon

如果我們觀察到有許多星星明顯 在一個空的點周圍繞軌運行時，

will be deflected in a phenomenon known as gravitational lensing.

很可能就是黑洞在帶領它們跳舞。

Most of the black holes that we've found can be thought of as two main types.

同樣的，路過的光 如果太靠近事件視界，

The smaller ones, called stellar mass black holes,

會因為所謂的重力透鏡效應而轉向。

have a mass up to 100 times larger than that of our sun.

我們所發現的黑洞 大部分可分為兩種主要類型。

They're formed when a massive star consumes all its nuclear fuel

比較小的叫做恆星質量黑洞，

and its core collapses.

質量比我們的太陽還要大一百倍。

We've observed several of these objects as close as 3000 light-years away,

當一個大質量的星星 消耗光了它所有的核燃料，

and there could be up to 100 million small black holes

它的核心會垮掉。

just in the Milky Way galaxy.

我們觀察到這些物體中 有幾個距離我們近三千光年，

So should we be worried?

光是在銀河當中，可能就有

Probably not.

高達一億個小黑洞。

Despite their large mass,

我們應該要擔心嗎？可能不用。

stellar black holes only have a radius of around 300 kilometers or less,

儘管恆星質量黑洞的質量很大，

making the chances of a direct hit with us miniscule.

它們的半徑只有 約三百公里，甚至更小，

Although because their gravitational fields

因此，直接衝向我們的機會非常小。

can affect a planet from a large distance,

不過，因為它們的重力場

they could be dangerous even without a direct collision.

可以在很遠的距離就影響到星球，

If a typical stellar-mass black hole were to pass in the region of Neptune,

即使沒有直接衝撞， 它們也具有危險性。

the orbit of the Earth would be considerably modified,

如果一個典型的恆星質量黑洞 通過海王星一帶，

with dire results.

地球的軌道可能會被大大地改變，

Still, the combination of how small they are and how vast the galaxy is

後果會很可怕。

means that stellar black holes don't give us much to worry about.

不過，黑洞非常小， 再加上銀河非常大，

But we still have to meet the second type:

也就是說，我們不需要 太擔心恆星質量黑洞。

supermassive black holes.

但我們仍然得要談談 第二種黑洞：超大質量黑洞。

These have masses millions or billions times greater than that of our sun

它們的質量比我們的太陽 大數百萬或數十億倍，

and have event horizons that could span billions of kilometers.

事件視界可達數十億公里長。

These giants have grown to immense proportions

這些巨物靠著吞噬物質

by swallowing matter and merging with other black holes.

以及跟其他黑洞合併 而變得如此巨大。

Unlike their stellar cousins,

和它們的恆星表親不同，

supermassive black holes aren't wandering through space.

超大質量黑洞不會在宇宙中閒逛。

Instead, they lie at the center of galaxies, including our own.

反之，它們會停留在銀河的中心， 包括我們的銀河。

Our solar system is in a stable orbit around a supermassive black hole

我們的太陽系的運行軌道是繞著 超大質量黑洞的穩定軌道，

that resides at the center of the Milky Way,

該黑洞就位在銀河的中心，

at a safe distance of 25,000 light-years.

保持兩萬五千光年的安全距離。

But that could change.

但那是有可能改變的。

If our galaxy collides with another,

若我們的銀河系 和另一個銀河系相撞，

the Earth could be thrown towards the galactic center,

地球可能會被拋向銀河中心，

close enough to the supermassive black hole

更靠近那個超大質量黑洞，

to be eventually swallowed up.

近到可能最後會被吞噬。

In fact, a collision with the Andromeda Galaxy

事實上，預測在四十億年之後

is predicted to happen 4 billion years from now,

就會和仙女座星系相撞，

which may not be great news for our home planet.

對於我們的家鄉地球來說， 這並不是好消息。

But before we judge them too harshly,

但在我們也不要 太嚴厲地評斷黑洞，

black holes aren't simply agents of destruction.

它們不只會帶來毀滅。

They played a crucial role in the formation of galaxies,

對於銀河系的形成， 它們也扮演了重要的角色，

the building blocks of our universe.

是我們宇宙的基礎建材。

Far from being shadowy characters in the cosmic play,

在這齣宇宙劇中， 黑洞演的並不是帶來陰影的角色，

black holes have fundamentally contributed

基本上，它們做出了很多貢獻，

in making the universe a bright and astonishing place.

讓宇宙成為一個明亮、 令人驚奇的地方。