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Thanks to CuriosityStream for supporting this episode!
本期节目由CuriosityStream赞助播出！
Go to CuriosityStream.com/Space to learn more.
在CuriosityStream.com/Space上可以了解更多详情。
Back in 2008, astronomers spotted a weird thing in our neighboring galaxy Andromeda.
2008年的时候，一些天文学家在附近的仙女座发现了一个奇怪的现象。
Without warning, a star suddenly flashed incredibly brightly!
在没有任何预警的情况下，一颗恒星突然不可思议的发出很亮的闪光。
But then, it faded back to normal over about fifteen days.
然后，在大概15天的时间里，又渐变回到正常状态。
And then, a year later, it did it again!
1年后，又重复出现这种情况！
Year after year, it kept on bursting into brightness and then settling back down.
年复一年，这颗恒星一直突然发亮，然后又黯淡下来。
Scientists named it M31N 2008-12a, which we'll call 12a for short.
科学家为它取名为M31N 2008-12a，我们在节目里就简称为12a吧。
And it turns out, this thing is something really special.
最后发现，这颗恒星很特别。
It's a rare phenomenon called a recurrent nova.
这是一种罕见的现象，名为再发新星。
And it may hold the key to understanding the lives and cataclysmic deaths of massive stars.
这颗恒星可能是一把钥匙，帮助我们了解一些大行星的生命和轰轰烈烈的消亡。
In 2008, though, scientists didn't realize how cool this thing was.
不过，2008年的时候，科学家还没有意识到这颗恒星有多酷。
They believed that the first flash of 12a was a plain old nova.
12a第一次发出闪光的时候，天文学家以为它只是一颗比较老的新星。
If you've heard of supernovas, the violent explosions that happen at the end of some stars' lives, well, these are totally different.
如果大家听说过超新星的话，那么你们应该已经知道，一些超新星会在生命末期发生强力爆炸，但这一次却完全不同。
So you can thank astronomers for that. Novas are much less destructive.
所以，大家可以感谢天文学家的新发现。超新星的破坏力不是那么强。
They originate from a very specific kind of binary star system:
他们起源于一种独特的双星体系。
a system with one normal star, and one small, dense white dwarf.
双星体系里有一颗正常的恒星，还有一颗密度很大、体型较小的白矮星。
The white dwarf has a pretty intense gravitational pull, so over time, it steals hydrogen gas from the outer layer of its neighboring star.
白矮星有很强的引力作用，所以随着时间的流失，白矮星会吸取其临近恒星外层的氢气。
Over the years, that gas builds up on the white dwarf's surface, where it gets hotter, and hotter, and hotter.
过去数年间，白矮星吸取的气体聚集在白矮星表面上，温度越来越高。
And when it reaches about twenty million degrees Celsius, nuclear fusion is kick-started within that outer layer.
当温度达到大概2000万摄氏度时，核聚变就在外层的内部开始发生了。
The stolen hydrogen is converted into heavier elements, and that reaction releases a huge amount of energy, starting a process called thermonuclear runaway.
吸取的氢气转变成了质量更大的元素，而核聚变在反应过程中也会释放大量能量，开启一个叫做热核暴涨的过程。
In this process, the fusion generates energy, which heats up the hydrogen more, which boosts fusion, which generates more energy and heat, and more fusion, and you get the idea.
在这个过程中，核聚变产生的能量会让氢气温度越来越高，而氢气温度越高，就越会促进核聚变，进而产生更多的能量和热量，然后又是更多的核聚变，所以大家就知道咋回事了吧。
Ultimately, that sudden release of runaway energy is enough to blast what's left of the stolen hydrogen and the fusion products outwards, away from the star.
最后，这种突然迸发的热核暴涨达到足以将所吸取氢气和核聚变产物向外喷发的程度，让其远离恒星。
And you end up with a really bright shell of material, lit up by the white dwarf and companion star within.
最后就留下特别明亮的壳体，壳体被白矮星和内部伴星所点亮。
From Earth, we see novas as sudden pulses of bright light that slowly fade over time, as their shells expand and dissipate into space.
地球上的我们将新星视为突然迸发的光，只是这种光会随着时间而逐渐变暗。在这个过程中，壳体会持续扩张并散布在宇宙中。
And generally, they're not that uncommon.
总体来说，这种现象不是很常见。
Astronomers see about 10 in the Milky Way every year, and at least 25 in Andromeda.
天文学家每年能在银河系里看到10次这种现象的发生，在仙女座里每年能看到25次。
But 12a was still special, because it wasn't just a regular, run-of-the-mill nova. It was a recurrent nova.
但12a依然是特殊的存在，因为12a不只是一颗普普通通的新星，而是再发新星。
In other words, after it blasted away all that gas, it kept stealing hydrogen from its companion star until it went nova again, and again, and again.
换言之，12a炸掉所有气体之后，会一直吸取伴星的氢气，直到自己再次成为新星，如此反复。
Once a year, every year, practically right on cue.
每年都是这个时候发生。
This wasn't the first recurrent nova scientists had ever seen, but it does seem to be the one that explodes the most often, since most objects like this only go off about once every decade or few decades.
这不是科学家发现的第一颗再发新星，但这颗新星似乎确实经常爆炸，因为大多数与此类似的物体大概都是每十年或者每几十年就会发生这样的情况。
And this behavior doesn't seem to be new, either.
这种行为似乎不是新现象。
In fact, based on how big the shell of material floating around 12a is, scientists think this nova has been regularly erupting for millions of years. As for why?
实际上，根据12a附近物质壳体的大小，科学家认为，这颗新星会在几百年的时间里定期爆炸。原因是啥呢？
Well, scientists think it happens because 12a's white dwarf is likely massive.
是这样的，科学家认为原因是12a的白矮星质量太大了。
With more mass, it has stronger gravity, so it can pull hydrogen from its companion more rapidly, and begin thermonuclear runaway in less time.
质量越大，引力就越大，就能迅速从伴星上吸取氢气，也可以在更短的时间里开始热核暴涨。
This recurrent nova is cool partly for that weird factor, like, a star that partially explodes every year? Yes please!
再发新星很酷的部分原因是这个奇怪的因素，每年都有一颗恒星发生部分爆炸吗？是的，就是这样！
But it might also have something important to teach astronomers.
但它可能也让天文学家了解了很多知识。
12a is so massive and is collecting so much hydrogen that, eventually, scientists believe it will reach what's called the Chandrasekhar Limit.
12a质量很大，收集了很多的氢气，最后，科学家认为12a会达到钱德拉塞卡极限。
That's the maximum mass a white dwarf can be and still be stable, so after that point, it will transform into some other kind of object.
这是白矮星在不影响稳定性的情况下所能达到的最大质量，等过了这个极限值，就会转变成另一种类型的物体。
There are a couple of ways this could happen, but researchers think that it's very likely to explode as a Type Ia supernova.
有几种方式可以让这个情况发生，但科学家认为，12a非常有可能会爆炸为Ia型的超新星。
These supernovas are famous for their consistency.
这种超新星以连贯性闻名。
Basically every Ia that goes off is known to have the same absolute brightness,
基本上，每颗爆炸的Ia都有同样的绝对亮度。
and this is so well-documented that these supernovas are part of a group nicknamed standard candles.
这一点有很多文献记录可以查询，这些超新星都属于一个叫做标准烛光的群体。
Scientists use them all the time to calculate how far away distant galaxies are, since their actual brightness goes down the farther away they are.
科学家一直是用它们来计算遥远星系的距离的，因为实际亮度会随着距离的增加而减弱。
This is incredibly useful, because it helps us measure the structure and expansion of the universe.
这个是非常有用的，因为它可以帮助我们评估宇宙的结构和扩张。
You know, big questions! But here's the catch: We still don't exactly know how type Ia supernovas happen.
你们懂的，这些都是很重要的问题。关键是：我们依然没有准确地得知哪种类型的Ia超新星会发生。
Our models can't quite explain it. So assuming 12a will go supernova someday, we have a unique opportunity to study a system that's potentially on the brink of destruction.
我们的模型暂时还无法解释。所以，假设12a有一天会变成超新星的话，我们就有一个独特的机会可以研究一个濒临毁灭的体系。
Seeing how it evolves could give astronomers precious information about standard candle supernovas, and by extension, our tools for measuring the universe.
观测超新星演变的过程可以为天文学家提供宝贵的数据，数据内容与标准烛光有关。继而就能成为我们评估宇宙的工具。
The only problem is that some researchers think it'll take another 40,000 years before 12a goes supernova.
唯一的问题在于：一些研究人员认为，需要再等4万年，12a才能变为超新星。
So we might have a little while to wait! But in the meantime, our new understanding of recurrent novas and the giant remnant shells that they leave behind will help us find more of these things.
所以咱们可且等呢！但与此同时，我们对再发新星和它们残存的大壳体也有了新发现——他们将帮助我们找到更多这样的物体。
And maybe we'll even catch one in the act of going supernova.
或许有朝一日我们还能捕捉到恒星变为超新星的过程。
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
If you enjoy our content and want to learn more about the universe, you might also like the documentaries on CuriosityStream.
如果你享受本期的内容，也想对宇宙了解更多的话，你或许会喜欢CuriosityStream上的纪录片。
They're a subscription-based streaming service with more than 2,400 titles, and they have some pretty great space content.
这款流服务是可以订阅的，有2400多个可订阅项目，空间也足够庞大。
Like, one series, called Cosmic Front, explores a bunch of stuff, from black holes to NASA's Space Shuttle program.
比如，有一个叫《宇宙先锋》的系列探索了许多内容，从黑洞到美国宇航局的航天飞机计划，不一而足。
And whether you've been a space fan for years or are just discovering the night sky, there's a good chance you'll learn something really cool.
而无论你已经是多年的太空迷，还是刚刚发现夜空的魅力，你都有很大的机会能了解到很酷的事情。
If you want to check it out, you can get unlimited access to CuriosityStream starting at just $2.99 a month.
如果你想试一下的话，只需2.99美元/月，就能无限获得CuriosityStream上的资源。
And for our audience, the first 31 days are totally free if you sign up at CuriosityStream.com/Space and use the promo code “space” during that process.
对《太空科学秀》的粉丝来说，前31天是完全免费的，只需要在CuriosityStream.com/Space上注册并使用“space”的优惠码即可。
When you sign up, you'll also be helping SciShow research and produce more episodes like this. So, thank you!
注册也是在帮我们的节目做调研，让我们可以制作出类似的更多节目，谢谢大家！
