When will the sun die?

太阳何时走到生命尽头？

If you worry about when the sun will die, never fear: that moment is billions of years away.

如果你担心太阳的寿命会终结，完全不必害怕：因为距离那一刻到来还有几十亿年的时间。

The sun gives energy to life on Earth, and without this star, we wouldn't be here. But even stars have limited lifetimes, and someday our sun will die.

太阳为地球上的生命提供能量。如果没有这颗恒星，我们就不会存在。但即使是恒星，其寿命也是有限的，总有一天我们的太阳也会走向生命的尽头。

You don't need to worry about this solar death anytime soon, though. Like all stars, a churning fusion engine fuels the sun, and it still has a lot of fuel left — about 5 billion years' worth.

不过，你无需担心太阳寿命的终结。就像所有的恒星一样，太阳内部翻腾着的聚变反应，为其提供着燃料，而且它仍有大量的燃料——可供燃烧大约50亿年之久。

Related: What's inside the sun? A star tour from the inside out

相关阅读：太阳里面有什么？由内而外的恒星之旅

Stars like our sun form when a huge cloud of gas (mostly hydrogen and helium) grows so large that it collapses under its own weight. The pressure is so high in the center of that collapsing mass of gas that the heat reaches unimaginable levels, with temperatures so hot that hydrogen atoms lose their electrons.

太阳这样的恒星形成于一个巨大的气体云（成分主要是氢和氦），该气体云不断增大，达到自身重量时，便坍缩成行星。在那团正在坍缩的气体中心，压力很高，热量达到了难以想象的高度，高温使得氢原子失去电子。

Those naked hydrogen atoms then fuse together into helium atoms, and that reaction releases enough energy to counter the intense pressure of gravity collapsing the cloud of gas. The battle between gravity and the energy from fusion reactions fuels our sun and billions of other stars in our galaxy and beyond.

然后，这些裸露的氢原子聚变成氦原子，这个反应释放出足够的能量来对抗强大的重力压力，使气体云坍缩。引力与聚变反应产生的能量之间的对抗为太阳和银河系内外数十亿其它恒星提供了燃料。

But in about 5 billion years, the sun will run out of hydrogen. Our star is currently in the most stable phase of its life cycle and has been since the formation of our solar system, about 4.5 billion years ago. Once all the hydrogen gets used up, the sun will grow out of this stable phase.

但在大约50亿年后，太阳将耗尽氢气。目前，它正处于其生命周期中最稳定的阶段，并且自太阳系形成45亿年以来一直如此。一旦所有的氢被用完，太阳就会从这个稳定的阶段中脱离出来。

With no hydrogen left to fuse in the core, a shell of fusion hydrogen will form around the helium-filled core, astrophysicist Jillian Scudder wrote in an article for The Conversation. Gravitational forces will take over, compressing the core and allowing the rest of the sun to expand.

天体物理学家Jillian Scudder在《对话》的一篇文章中写道，由于没有氢原子在核心进行聚变，一个聚变氢壳将以氦气为核心形成。引力将起作用，压缩核心并允许太阳的其余部分膨胀。

Our star will grow to be larger than we can imagine — so large that it will envelope the inner planets, including Earth. That's when the sun will become a red giant, which it will remain for about a billion years.

我们的恒星将会变大到超乎我们的想象——大到它将包住地球在内的内行星。那时太阳将成为一个红巨星，并保持大约10亿年。

Then, the hydrogen in that outer core will deplete, leaving an abundance of helium. That element will then fuse into heavier elements, like oxygen and carbon, in reactions that don't emit as much energy. Once all the helium disappears, the forces of gravity will take over, and the sun will shrink into a white dwarf. All the outer material will dissipate, leaving behind a planetary nebula.

然后，外核中的氢将会耗尽，留下大量的氦。接着，氦元素会通过不释放出那么多能量的反应，聚变成较重的元素，如氧和碳。一旦所有的氦消失，重力就会起作用，使得太阳缩小成一颗白矮星。所有的外层物质都会消散，留下一个行星状星云。

"When a star dies, it ejects a mass of gas and dust — known as its envelope — into space. The envelope can be as much as half the star's mass," astronomer Albert Zijlstra of the University of Manchester in the United Kingdom, said in a statement. "This reveals the star's core, which by this point in the star's life is running out of fuel, eventually turning off and before finally dying."

英国曼彻斯特大学的天文学家阿尔伯特•齐尔斯特拉在一份声明中说：“当恒星死亡时，它会向太空喷射出大量气体和尘埃——称之为包层。包层的质量可以达到恒星质量的一半。”“这揭示了恒星的核心：它的生命正在消耗燃料，最终熄火，然后死亡。”

Astronomers estimate that the sun has about 7 billion to 8 billion years left before it sputters out and dies. One way or another, humanity may well be long gone by then.

天文学家估计，太阳在喷射包层，走向生命尽头之前，大约还有70亿到80亿年的时间。无论如何，到那时，人类很可能早已灭绝。

Our sun isn't massive enough to trigger a stellar explosion, called a supernova, when it dies, and it will never become a black hole either.

当太阳生命终结时，它的质量不足以引发恒星爆炸，即产生超新星，而且它也永远不会成为黑洞。

In order to create a supernova, a star needs about 10 times the mass of our sun. An object of that size would form a dense stellar corpse called a neutron star after the explosion.

为了创造一颗超新星，一颗恒星需要大约10倍于太阳的质量。如此大的物体在爆炸后会形成一个致密的恒星“遗体”，称为中子星。

To leave behind a black hole, a supernova must occur in a star with about 20 times the mass of the sun.

要留下黑洞，超新星必须产生在质量约为太阳20倍的恒星中。

Find out what will happen to the Earth when the sun dies, from Live Science. Learn more about how stars form, evolve and die from NASA, and learn more about how the agency studies our sun. Watch a mini documentary on the topic, The Death of the Sun, from PBS Space Time.

关注Live Science，了解当太阳消亡时地球将会发生什么。关注NASA，了解更多关于恒星如何形成，演化和死亡的信息，以及更多关于该机构如何研究太阳的信息。关注PBS时空频道，观看一个主题为“太阳之死”的迷你纪录片。

Gesicki, K., "The mysterious age invariance of the planetary nebula luminosity function bright cut-off," Nature Astronomy (2018). https://www.nature.com/articles/s41550-018-0453-9

Gesicki，K.，“行星状星云光度函数明亮截止的神秘年龄不变性”，《自然天文学》(2018年）。https：//www.nature.com/articles/s41550-018-0453-9

NASA, "Our Sun — In Depth," last updated Oct. 15, 2021. https://solarsystem.nasa.gov/solar-system/sun/in-depth/

美国宇航局，“我们的太阳-在深度”，最新更新于2021年10月15号。https：//solarsystem.nasa.gov/solar-system/sun/in-depth/

NASA, "Why the Sun Won't Become a Black Hole," Sept. 26, 2019. https://www.nasa.gov/image-feature/goddard/2019/why-the-sun-wont-become-a-black-hole

美国宇航局，“为什么太阳不会变成黑洞”，2019年9月26号。https：//www.nasa.gov/image-feature/goddard/2019/why-the-sun-wont-become-a-black-hole