恒星是如何燃烧数十亿年的?

这是一个很好的问题。我想我会分两部分给出答案。不是只有你一个人认为它们很快就会燃烧殆尽。大约一百年前，这是物理学中真正的热门话题之一。大约在20世纪初，有一位著名的物理学家叫开尔文勋爵。他对太阳应该存在多久做了一个粗略的计算，得出的答案是几百万年。他想象太阳像气体火一样燃烧，然后说，好吧，它可以持续1000万年所以进化论一定是错的。没有足够的时间让动物进化。他用这个来反驳达尔文当然他完全错了，对吧?他不理解的那块缺失的拼图是太阳用来产生能量的过程被称为核聚变。 And it's extraordinarily efficient. You get an enormous amount of energy out of a really, really tiny amount of matter. Um, it's dictated by this very famous equation. E=mc squared. E is energy, m is mass, and c is the speed of light, which is a very big number. So C squared is an enormous number. So what e equals mc squared is really telling you is that a tiny, tiny bit of mass gives you an enormous amount of energy. Stars are very, very efficient. The other half of the answer is that stars are just really, really big. So even if they are churning through fuel at an enormous rate, they can still last a very long time. The sun burns through several million tons per second, which sounds unbelievable, right? You think that wouldn't be sustainable at all. But if you go and calculate it down maybe use your number sense, right? If you get a calculator to work out how many seconds in a year, multiply that by 10 billion years and multiply that by a million tons of seconds, you don't get to even a fraction of 1% of the sun's mass, right? So the sun can happily burn a million tons of seconds for billions of years and still be absolutely fine. And it's all down to the efficiency of E=mc squared.

Chris -有一点是恒星的大小很重要，不是吗?因为如果你是一颗非常大的恒星你有大量的燃料和大量的重力和质量把它们聚集在一起，你会变得非常非常热，非常非常快。但你也会更快地消耗掉所有的燃料。所以大恒星比小恒星燃烧得更快更亮。

马特-对，没错。这几乎是违反直觉的，对吧?你会想，“大恒星，更多的燃料，它会持续更长的时间”。但大明星确实活得快，死得早。它们燃烧得非常热，它们燃烧燃料的速度比小恒星快得多。所以像太阳这样很小的恒星，会持续大约100亿年。那大概是10亿年左右。一颗巨大的恒星可能会持续1000万年，这听起来很长。与太阳相比，它只是一眨眼的功夫。一颗小小的冷红矮星的寿命可能比宇宙的年龄还要长。

克里斯-谢谢你，马特。