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This episode is sponsored by The Ridge.
本期节目由The Ridge赞助播出。
Go to ridge.com/scishow and use promo code scishow to get 10% off your next order.
在ridge.com/scishow上可以使用优惠码scishow来获取下一单10%的减免。
When you think of the universe, you probably think of all the bright stuff.
每次想到宇宙的时候，大概你想到的都是明亮的东西。
Stars and galaxies that light up the night sky. And that's understandable.
星星和星系点亮了夜空之类的。这种想法是可以理解的。
I mean, in between those things, it looks like there's a lot of emptiness.
我是说，在这些东西之间，看起来有很多虚空。
But more than half of all the matter in the universe is out there in the dark, filling that empty space.
但宇宙里半数以上的物质都处在这黑暗中，填满了看似虚空的宇宙。
And I'm not talking about dark matter or anything like that.
我讨论的不是暗物质之类的东西。
I'm talking about the intergalactic medium. It's the thinly-spread gas in the space between galaxies.
我讨论的是星系间介质——宇宙中星系之间稀薄分散的气体。
And even though it's basically invisible, it has a lot to tell us about the stuff we can see.
虽然暗物质基本上是不可见的，但暗物质可以告诉我们很多有关可见物质的信息。
The intergalactic medium, or IGM, glows extremely faintly, so it's invisible to most telescopes.
星系间介质（IGM）所发的光很微弱，大多数望远镜都看不到。
In fact, it wasn't even discovered until the 1960s.
实际上，直到20世纪60年代才发现。
That's when scientists first discovered quasars, incredibly bright objects in the old and distant universe.
那时候，科学家第一次发现了类星体——古老遥远的宇宙中异常明亮的物体。
Oddly, when they looked at these quasars, they found lots of wavelengths missing from their light.
奇怪的是，当科学家观测这些类星体时，他们发现了其中缺失了许多波长。
Normally, light from stars is a continuum of all wavelengths.
正常情况下，恒星发出的光，其波长是连续统一的。
And by splitting that light apart, kind of like you do with a prism, you can see a continuous rainbow, or a spectrum.
将光分散开来之后，就像用棱镜产生的效果那样，就能看到持续的彩虹——光谱。
But there are often gaps in that spectrum. You get gaps when there's something sitting between the light source and your telescope, absorbing specific wavelengths of light before they reach you.
但这光谱是有间隔的。当光源和望远镜之间存在什么东西的时候，就会出现间隔。因为中间的东西会吸收特定的波长，然后光才会抵达望远镜里。
That's what astronomers were seeing in the spectra from these quasars, so they knew there had to be invisible matter sitting between us and these distant objects.
天文学家在类星体中观察到的也是这样，据此，天文学家就知道这些遥远的物体和我们之间一定存在着不可见的物质。
They could even tell what it was made of. The patterns of absorbed lines told astronomers that this gas was mostly hydrogen with some heavier elements thrown in, like carbon, silicon, and oxygen.
甚至能据此推测出这些物质的成分。被吸收的线条所呈现的样子让天文学家知道——这个气体基本上由氢气组成，其中也有一些质量较大的元素，比如碳、硅、氧。
In general, the IGM is extremely thin, on average, it has less than one atom per cubic meter.
总体来说，IGM非常稀薄，每立方米平均只有不到一个原子。
But around galaxies, gravity is able to hang onto a somewhat denser halo of gas, which scientists call the circumgalactic medium.
但在各星系附近，引力作用可以依附在密度较大的气体光环上，科学家称其为环星系介质。
And even though the gas in both of these regions is thin and invisible, it's closely tied to the life cycle of galaxies, and has a lot to tell us about how they form and evolve.
虽然这2个区域的气体都很稀薄且不可见，但这跟各星系循环的生命是有关系的，能让我们了解很多它们的形成方式和演化方式。
These days, astronomers have some new tools for studying the IGM, but a lot of the time, they still use the same old technique.
近来，天文学家有一些新工具可以研究IGM，但很多时候，他们用的依然是之前的技术。
After all, studying the gaps in spectra can tell us about the temperature, distance, age, chemistry, and motion of the gas in front of the light source.
毕竟，研究光谱的间隔可以让我们了解温度、距离、年代、化学过程、气体在光源前的运动。
Which is a lot to know about an invisible gas billions of light-years away!
对于这种距离我们数十亿光年远的不可见气体来说，我们可以据此了解很多信息了！
The really cool thing is, since quasars are so old, by exploring their spectra, we can actually explore gases from the early universe, their light is carrying information that's billions of years old.
很酷的是：类星体年岁很久了，所以，通过研究类星体的光谱，我们就能探究宇宙初期的气体，它们的光线中蕴藏着数十亿年前的海量信息。
Astronomers are even able to look back to when the early universe gave birth to the first stars and galaxies, just hundreds of millions of years after the Big Bang.
天文学家甚至能回顾到宇宙初期刚产生第一批恒星和星系时候的样子，就是宇宙大爆炸数千万年前的样子。
Back then, clouds of gas were made of pure hydrogen, and in them, astronomers can see clumps, some slightly denser and hotter spots separated by thinner gas in-between.
那时候，许多气体云都是由纯氢气组成的，天文学家可以在其中观测到块状物质——密度更大一些、温度更高一些的点，被其中稀薄的气体分隔开来。
And those hot clumps of hydrogen? Those are the beginnings of the universe's first galaxies!
而这些高温氢气块呢？这些是宇宙初期星系开始的样子哦！
By using those clumpy spots as a starting point, scientists have been able to simulate the evolution of the universe, and better understand how we got the universe we live in today.
通过把这些块状物作为着手点，科学家能够模拟宇宙的进化情况，更好地了解我们今天所生活的宇宙是如何演化而来的。
These days, the IGM still makes up 60% of matter in the universe.
近来，IGM依然占宇宙物质的60%。
But it's not the same old gas that was there all along.
但这并不是一直都在那里的气体。
Now it has a lot more heavy elements that were forged in stars, because galaxies are constantly trading material with the IGM.
现在，这里有很多在恒星中形成的重元素，因为一些星系一直在跟IGM交换物质。
Gas likely gets blown out of active galaxies by things like violent supernovas, black hole jets, and solar winds.
气体很有可能是在剧烈超新星过程中从活跃星系黑洞喷射、太阳风中迸发出来的。
Violent events like galactic mergers can also toss a huge amount of dust out of a galaxy.
一些剧烈的活动，比如星系合并，也可以从星系中抛出大量尘土。
This seems to explain how the intergalactic medium got its sprinkle of heavy elements.
这似乎可以解释为何星系间介质为何会出现重元素的闪光。
But galaxies aren't just blowing out gas; they're also pulling it in.
但一些星系不只迸发出气体，还会吸取气体。
Once the circumgalactic gas moves away from the hot, turbulent environment of the galaxy, it cools down.
等星系间气体从高温活跃的星系环境中离开后，温度就会降低。
As it slows, it becomes more susceptible to the galaxy's immense gravitational pull, and some of it falls back into the galaxy.
随着温度的降低，这些气体就更容易受星系强大吸引力的作用，有一部分气体就会回到星系中。
This cycle of inflowing and outflowing gas is known as galactic recycling.
这个流入流出的循环就是银河系回收。
Models suggest that galaxies typically pull in about one solar mass of gas a year.
一些模型显示，一些星系一般一年会吸收大概1个太阳质量的气体。
And this infalling gas is what keeps a galaxy alive!
这些流动的气体是星系长青的关键！
That's how a galaxy can keep making new stars.
这是星系持续产生新恒星的方式。
Recycling doesn't seem to be a perfect loop, though.
不过，回收似乎不是一个完美的循环。
A 2019 study of our own galaxy revealed that more gas was flowing in than out.
2019年，我们对自己的星系做了一项研究，该研究表明，更多气体会流入，而非流出。
So the Milky Way must be getting a boost of gas from somewhere.
所以银河系一定是从某处获取了一些气体。
Since our galaxy is one of the biggest in the neighborhood, it may be leeching circumgalactic gas from smaller, neighboring galaxies.
由于银河系是附近区域里最大的星系之一，所以或许它会从临近的一些较小的星系中吸取气体。
Or it's possible that this gas is blowing in from deeper in the intergalactic medium.
有可能气体是从星系间介质更深的地方流入的。
Either way, we don't have all the answers yet, but scientists hope that similar measurements from other galaxies could tell us more about how galaxies interact with intergalactic gas.
无论是哪种方式，我们还没有完整的答案，不过，科学家希望对其他星系所做的类似测量可以告诉我们更多有关星系与星系间气体做互动的方式。
Measurements like this could also help to answer the question of why galaxies die.
类似这样的测量有助于解答星系消亡的原因。
Because it's not exactly obvious. As long as galaxies are recycling gas, it seems like they could keep making stars forever.
因为原因目前并不明显。只要星系还在回收气体，似乎就能源源不断地产生恒星。
But they don't. We see lots of galaxies whose stars are all red and old, with no youngsters in the mix.
但并非如此。我们看到许多星系的恒星全是红色的，而且年岁很大了，其中并没有年轻的恒星。
But it's not clear why. Observations of the area around dead galaxies show that there is still gas that's cool enough to fall in.
但目前尚不清楚这其中的原委。我们对消亡星系附近的区域做了观察，观察发现还有一些温度较低的气体可以吸入。
But for some reason, it doesn't. Scientists don't know what's stopping it, but whatever the answer is, it's probably in the gas between galaxies.
不过，出于某些原因，并没有吸入。科学家不知道阻止这一切发生的原因是什么，但无论原因是什么，大概都在星系间气体中。
Researchers hope that future surveys of dead galaxies and their circumgalactic halos will offer more clues.
科学家希望，未来对消亡星系的研究以及银河系附近光环的研究能提供更多的线索。
The space between the stars is still pretty murky territory, but as we get better at exploring it, the intergalactic medium will have a lot to tell us about how galaxies live and die.
恒星间的空间依然是模糊地带，不过随着我们探索能力的增强，星系间介质能告诉我们很多关于星系运作和消亡的方式。
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如果你经常出门的话，你大概不想带着无用的东西，比如发票、小零钱、过期的礼品卡等等。
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The Ridge可以帮助大家带更少的东西，但都是刚需品。
The Ridge began with a father-and-son team that launched their first product, the Ridge Wallet, on Kickstarter in 2013.
The Ridge是父子团队创建的，他们的第一个产品是Ridge钱包，这款产品于2013年在Kickstarter上推出的。
It's sleeker than a traditional wallet, with just two metal plates bound by an elastic band.
它比传统钱包更便捷，用弹力带帮着2片金属板。
Now it sits in pockets of more than half a million people.
现在，已有50多万用户在使用了。
The Ridge also makes backpacks, phone cases, and other products, with over 30,000 five-star reviews.
The Ridge也出售背包、手机壳等产品，有3万多个五星好评。
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如果你喜欢的话，可以终身保修，如果不喜欢，还可以免费退货。
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今天可以获得10%的减免，全球包邮包退，可戳ridge.com/Scishow并使用优惠码购买。
You can find a link in the description.
描述中有链接哦。
