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Most of what we know about the inside of our planet comes from looking down and studying Earth's interior itself.
我们对地球内部的了解大部分都来自于俯瞰和对地球内部本身的研究。
But there's still a lot we don't know about our planetary home, and scientists are always looking for better tools to help us learn more.
但我们对地球仍有许多不了解的地方，科学家们总在寻找更好的工具来帮助我们了解更多。
And just last week, a group of physicists announced that we might be getting a new one.
就在上周，一群物理学家宣布他们可能找到了一种新工具。
And a paper published in the journal Physical Review D,
在一篇发表在《物理评论D》杂志上的论文中，
they calculated that a detector that's already being built will be able to study Earth's interior using neutrinos,
他们预测正在建造的探测器将能够利用中微子研究地球内部，
some of the most elusive particles in the universe, which are constantly raining down on us from space.
中微子是宇宙中最难以捉摸的粒子，它们不断地从太空落入地球。
We learn a lot about the inside of our planet from earthquakes.
我们从地震中学到了很多地球内部的知识。
For example, based on the types of ripples we detect from an earthquake, we can tell if it traveled through a layer of liquid.
例如，根据我们从地震中探测到的波纹类型，我们可以判断它是否穿透了一层液体。
By combining what we know about how ripples travel through matter with measurements of things like gravity,
结合重力测量法等方法，我们可以判定波纹的传播方式，
scientists have formed pretty good models of what Earth and other planets look like beneath the surface.
科学家们已经构建了地球和其他行星地表之下的完美模型。
But today's methods leave a lot of unanswered questions still, like how different layers of rock move and change to let heat flow through the inner Earth.
但这些方法仍遗留了许多未解之谜，如不同的岩石层如何移动和变化，使得热量穿透地心。
The authors of this new paper argued that's where neutrinos can help:
这篇新论文的作者提出中微子可以做到：
The way they travel through the Earth can give us a brand-new way of understanding its internal structure.
它们穿越地球的方式为我们提供了理解其内部构造的全新方式。
Neutrinos are tiny particles that hardly ever hit anything else,
中微子是微小粒子，几乎不会撞到其他东西，
and they come in three types, called flavors: electron neutrinos, muon neutrinos, and tau neutrinos.
它们有三种类型，称为“味”，即电子中微子，μ子中微子和τ中微子。
But a neutrino doesn't always stay the same flavor.
但是中微子不总是保持一种“味”，
It can switch between flavors as it travels.
在它飞行的过程中会在两种“味”之间转换。
And even though they hardly ever directly interact with other matter,
即使它几乎不与其他物质直接发生反应，
the density of matter around a neutrino helps determine how quickly it switches between flavors.
但中微子周围物质的密度决定着它在不同味之间转换的快慢。
Generally, they spend more time as electron neutrinos in denser matter.
一般来说，它们在密度大的物质中，保持电子中微子状态的时间会更长。
And the team pointed out that we can use this weird property to study Earth's interior.
这个小组提出我们可以利用这一超自然物质研究地球内部。
For example, if we see more electron neutrinos among the neutrinos that have passed through certain parts of the planet, we know those parts are denser.
例如，如果我们在中微子中看到更多的电子中微子穿过地球的某些部分，我们就知道这些部分密度较大。
Versions of this idea have been around for a few years, but we haven't had detectors sensitive enough to tell us how the number of extra neutrinos changes when they travel through different parts of the Earth.
人们有这个想法已经很多年了，但我们没有足够灵敏的探测器告诉我们，当中微子穿越地球的不同部分时，额外的中微子数量会发生怎样的变化。
So these authors carefully calculated how sensitive a detector would need to be for this fine-grained measurement.
因此，这些作者仔细地计算了探测器需要对这种细粒度测量的敏感程度。
And they showed that a detector called DUNE, which should be operational in 2027,
他们展示的探测器叫做“DUNE”，应该在2027年投入使用。
will finally be able to measure Earth's internal structure using neutrinos.
它将能够利用中微子测量地球内部结构。
So within a decade, we might be using the universe's ghostliest particles to study our own little planet.
所以十年之内，我们就有可能利用宇宙的幽灵粒子来研究我们的地球。
Meanwhile, other researchers are looking into some of the strangest galaxies we've ever seen.
与此同时，其他的研究人员正在观察一些我们见过的最奇怪的星系。
In this week's Nature, a group of astronomers published a study on jellyfish galaxies,
在本周的《自然》杂志上，一群天文学家发表了一项关于水母星系的研究，
and what they can teach us about why some supermassive black holes suddenly start feasting.
它们能告诉我们为什么一些超大质量的黑洞突然开始享受盛宴。
And yeah, jellyfish galaxies are a real thing!
是的，水母星系是真实存在的！
Galaxies speed toward or away from the stuff around them at hundreds of thousands of kilometers per hour.
星系以每小时数十万公里的速度接近或远离它们周围的物质。
But as they travel, some galaxies ram into what's called the intracluster medium, or ICM:
但当它们行进时，一些星系会撞到所谓的内部介质，即ICM：
Huge pockets of gas that aren't connected to any particular galaxy.
ICM是巨大的气孔，没有与任何特定的星系相连。
And when a galaxy passes through the ICM, its own gas can get dragged behind as it tries to push the ICM out of the way.
当星系经过ICM时，它试图把ICM推到一边，但它自身的气体可能会被拖到后面。
This leaves long threads of gas and dust trailing behind the galaxy, making it look a lot like a jellyfish.
这就使得星系后面留下了长串的气体和尘埃，使它看起来很像水母。
When the team started studying a set of jellyfish galaxies, they noticed a connection to an unsolved problem in astronomy.
当这个小组开始研究一组水母星系时，他们注意到了天文学中一个未解之谜与之相关。
Almost all of the jellyfish galaxies had really active supermassive black holes at their centers that were eating lots of gas and stars.
几乎所有水母星系的中心都有活跃的超大质量黑洞，它们吞噬了许多气体和星球。
Just about all galaxies have supermassive black holes at their centers, but usually they're not doing very much; gas and stars just orbit around them.
所有星系中心都有超大质量黑洞，但通常它们作用不大，气体和恒星只是围绕它们旋转。
Very occasionally, though, huge quantities of gas and stars are sucked toward the black hole, where they either fall in or get flung away with huge amounts of energy.
不过非常偶然，大量的气体和恒星被吸入黑洞，它们要么掉入黑洞，要么被大量的能量抽走。
When that happens, astronomers will say that the galaxy or black hole is active.
当这种情况发生时，天文学家称星系或黑洞是活跃的。
And they aren't exactly sure what flips the switch from a black hole with gas and stars quietly orbiting it to one with stuff actively diving into it.
但他们也不非常确定的是，气体和恒星本来围绕黑洞旋转，是什么使得它们被吞噬了？
The fact that all these jellyfish galaxies also had active black holes was an interesting connection,
所有这些水母星系也有活跃的黑洞，这是一个有趣的联系。
and the team wanted to know which came first: the active black holes or the jellyfish tentacles?
但这个小组想知道哪一个先发生：活跃的黑洞或水母触角？
If the black holes were active before the galaxies hit the ICM and became jellyfish,
如果黑洞在星系撞击ICM成为水母星系之前是活跃的，
some of the material falling in toward the black holes might've missed and been flung out into the trails behind the galaxy, making even bigger jellyfish than would've otherwise been.
那么一些落入黑洞的物质可能消失被抛到星系后面的轨迹上，使得水母星系变大。
But if the galaxies' black holes were quiet before, the collisions with the ICM might've pushed a whole bunch of gas into the center to get eaten up, making the black holes active.
但如果星系黑洞之前是平静的，与ICM的碰撞可能将一大堆的气体推入其中心被吞噬，使得黑洞活跃起来。
By measuring the galaxies' speeds and where they were in their cluster,
通过测量星系的速度和它们的聚集点，
the authors found that for these jellyfish, collisions with the ICM almost certainly came first and activated the black holes.
研究人员发现这些水母星系先与ICM碰撞，再激活黑洞。
Almost all the jellyfish were moving quickly enough through the dense ICM that lots of gas would've been pushed toward their centers.
大多数水母星系非常快速地穿过密集的ICM，使得大量的气体被推入它们的中心。
And the one galaxy they observed that didn't have an active black hole was moving really slowly compared to the others,
他们观测的一个没被激活黑洞的星系与其他星系相比，移动得很慢。
meaning that it probably wasn't moving fast enough to have its gas pushed into the center.
这意味着它的移动速度可能不够快，无法将气体推入中心。
Astronomers already know that galaxy mergers and other large events can force gas toward a galaxy's central black hole, activating it.
天文学家们已经知道，星系合并和其他大事件可以迫使气体进入星系中心的黑洞并激活它。
But this new paper shows that something as minor as passing through a random pocket of gas can set galaxies off,
但这篇新论文显示，从任意气孔中穿过的小东西也可以激活黑洞。
which might explain a bunch of active, non-jellyfish galaxies, too.
这可能也解释了一群活跃的非水母星系的存在。
They might've slammed into something that pushed gas toward their centers, even if they didn't come out looking like jellyfish afterward.
它们可能撞到了某些东西，将气体推到它们的中心，即使它们之后看起来不像水母。
So that's one more reason to study some of the weirdest-looking galaxies out there: they can teach us a lot about all kinds of processes happening in the universe.
所以研究一些奇怪的星系又多了一个原因：它们可以教给我们很多宇宙中发生的各种发展过程的知识。
If you'd like to learn about some more weird galaxies, you can check out our video about three galaxies that astronomers are pretty sure shouldn't exist.
如果你想了解一些更奇怪的星系，你可以看看我们的视频，即天文学家肯定不应该存在的三个星系。
