And if one of those clouds of dust and gas is massive enough, its own gravity causes it to start to collapse so it folds in on itself towards the center of that cloud.

如果其中一團塵埃和氣體足夠龐大，它自身的引力就會導致自體向中央崩塌。

It gets denser and denser, and hotter and hotter.

它會變得越來越稠密，溫度也越來越高。

And eventually, the particles of that the gas and the dust are made of are brought so close together that they start to stick together, they start to fuse.

最終，構成氣體和塵埃的分子聚合得非常密集，黏著在一起，開始融合。

That's the energy source of a star.

這就是一顆星星的能量來源。

The star switches on and begins to shine.

星星甦醒了，開始發光發亮。

Inside every newborn star hydrogen atoms are fused together to make helium.

在每一顆新生的星星內部，氫原子融合在一起製造氦氣。

This process is called fusion, and it creates the energy of every star.

這個過程叫做「核聚變」，每顆星星的能量都來自於此。

What happens to a star during the rest of its life depends on how massive it is at its birth.

星星在餘生會遭遇哪些事，都取決於它誕生時有多龐大。

A star like the sun is in a delicate balance between gravity, which wants to make the star collapse in on itself, and the pressure that pushes outward that comes from the energy produced in these fusion reactions at its core.

如太陽一般的星星就處於一種微妙的平衡狀態，一方面自身的引力想讓它崩塌，另一方面核融合製造出的能量卻又帶來向外的推力。

However, at some point in the future, the hydrogen runs out.

在未來的某一刻，氫氣終將耗盡。

At that point, the core of the star will start to collapse in on itself under its own weight.

這時星星的中央將會因為自身的重量而崩塌。

It gets denser, it gets hotter until the point where you can actually start to use the helium atoms themselves as the fuel for the fusion, pushing helium atoms together, making carbon and oxygen, the next heavier elements on the periodic table.

它會變得越來越稠密、越來越高溫，直到可以直接利用氦氣作為核融合原料，使氦原子聚合，製造出碳和氧，週期表上較重的元素。

As the star begins to fuse helium, it creates more energy and that causes the outer layers of the star to expand.

星星一旦開始利用氦氣進行核融合，就會製造更多的能量，使星星的外層開始擴張。

One day, our sun will grow so large it will swallow up the inner planets of the solar system out as far as the Earth!

有一天，我們的太陽會擴張到足以吞噬太陽系內圈的星球，包含地球！

It will become a red giant.

它會成為一顆紅巨星。

For the sun, this will be the beginning of the end.

對太陽來說，這將會是結束的開端。

What happens is that the outer layers of the star get farther and farther from the middle.

事情是這樣的，星星的外圍變得離核心越來越遠。

The force of gravity that they feel is getting weaker.

它們感受到的引力變弱了。

And, actually, the star loses hold of its outer atmosphere.

然後星星其實就會失控，無法控制自己的外部大氣層。

Its outer atmosphere drifts off out into space.

它的外部大氣層會漂流到外太空中。

It expands to become a planetary nebula.

擴張到成為行星狀星雲。

And they're some of the most beautiful objects in the universe.

它們是宇宙中最美麗的幾樣物體。

Once the outer layers have drifted away, all that is left of the star is its core.

一旦外層全飄走了，星星就只剩下它的核心。

A white dwarf star is the dead, remnant core of a star like the sun at the end of its life.

如太陽一般的星星在生命末期死亡時，將會只剩下核心，稱為白矮星。

What's left behind is something that might weight as much as 1/2 the mass of the sun but it's only about the size of the Earth, so it's an incredibly dense object.

剩餘的殘核大概會有太陽一半的重量，體積卻只有地球的大小，所以是一種密度極高的物體。

It's dead, there's no nuclear fusion going on anymore, it's incredibly hot but then over millions of years, it will gradually cool down to become a black dwarf.

它已經死了，再也沒有任何的核融合反應，溫度極高，不過在未來的百萬年內，將會慢慢冷卻成為一顆黑矮星。

Some stars, however, are much more massive than the sun and they lead very different lives.

然而，有一些星星比太陽要巨大多了，它們過的生活非常不同。

They are able to fuse heavier and heavier elements inside their core.

它們的核心能夠一再融合重量越來越重的元素。

The star gets bigger and bigger.

星星變得越來越龐大。

Some grow up to 1000 times the size of our sun until it has fused elements all the way up to iron.

有些會用鐵進行核融合，長得比我們的太陽大上一千倍！

And once we've formed an iron core, there's no more energy that can be got from fusion.

一旦形成鐵核，核融合就無法再提供任何能量了。

That core collapses.

核心崩塌。

The rest of the star starts to collapse in after it but then it bounces off.

星星其餘的部分開始隨之崩塌，但之後會反彈。

There's a huge shock wave.

會有一波巨大的衝擊波。

And in just a second: BANG!

一秒之間，嘣！

The outer parts of the star are blasted off in to space in a huge super-nova explosion!

在一場巨大的超新星爆炸中，星星的外部構造被射進外太空！

These super-nova explosions are so powerful that when one of these stars explodes, it can actually outshine the whole galaxy of which is part... a galaxy of maybe a 100,000 million stars.

這些超新星爆炸威力無窮，只要有一顆星星開始爆炸，它將照亮一整個星系，一個或許含有一千億顆星星的星系。

For these super giant stars, all that is left is a super dense core known as a neutron star, an object that can have a mass greater than our sun but be less than 20 kilometers across.

這些超級巨星最後成為「中子星」，也就是一個密度極高的核心，可能重於我們的太陽，直徑卻不到 20 公里。

But for the most massive stars of all, we think, that when the core collapses the gravity is so strong, it becomes a black hole from which not even light can escape.

但我們推論，其中最龐大的星星崩塌時，引力會太過強大，最後成為一個連光都能吞噬的黑洞。

So stars are actually the places in the universe where the elements are created.

所以星星其實就是宇宙中元素誕生的地方。

After the Big Bang, our universe contained only hydrogen and helium.

在大爆炸發生後，我們的宇宙只存有氫氣和氦氣。

All the other, heavier elements were therefore fused inside stars.

其他所有比較重的元素都是在之後由星星融合而來。

The amazing thing is that virtually everything you see around you was made inside a star billions of years ago before the sun and planets were formed.

驚人的是，你目光所及的所有事物其實都是誕生自幾十億年前的星星，早在太陽和行星形成以前。

And when that star died and blasted its guts out into space that formed the raw materials from which our sun the planet earth and indeed ourselves were made.

當星星死亡、吐出五臟六腑到外太空時，提供了形成太陽、地球的元素，也形成了我們自己。

And actually I think, ultimately, that's one of the major reasons why I think understanding stars is crucial, because it's actually telling us where we came from.

這也是為什麼，我認為我們必須要了解星星，因為它們其實訴說了我們從何而來。