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Galaxies are all over the news this week!
本周，有关星系的新闻霸占了各大版面。
Galaxies near, galaxies far, galaxies wherever you are and, yes, that does mean the Milky Way.
是指附近的星系、遥远的星系，还是指哪里的星系呢？没错，是指银河系。
But first, in a paper published this week in the journal Nature,
但是在本周《自然》期刊上发表的一篇论文中，
an international team of astronomers discovered that a distant galaxy has almost no dark matter, throwing our expectations straight out the window.
国际上的一组天文学家发现，附近的一个星系几乎不含有暗物质，这让我们大跌眼镜。
Dark matter isn't so much dark as it is invisible to all current methods of detection.
暗物质的“暗”在于其不可为现有的手段探测到。
It doesn't interact with light at all, so we can't see it, but it does have mass, so we can see the effects of its gravitational pull.
暗物质不会与光发生相互作用，所以我们看不到，不过由于暗物质是有质量的，所以我们能看到暗物质万有引力的作用。
In most galaxies, dark matter is more abundant than regular, or baryonic, matter.
大多数星系中的暗物质都要比常规的重子物质数量更多。
In our own Milky Way it outnumbers baryonic matter roughly 30 to 1, but in dwarf galaxies, that ratio is over 10 times greater!
在我们的银河系，暗物质的数量超过了重子物质，比例大概是30比1，但在矮星系中，这个比例只有10倍多一点。
So to find a small galaxy with almost no dark matter at all would be super weird. So, obviously, we found one.
所以如果某个小星系里没有暗物质的话，会让人匪夷所思，所以，我们显然已经发现了一个。
It's called NGC1052–DF2, although we'll just call it DF2 for short.
这个星系名为NGC1052–DF2，我们经常简称它为DF2。
To figure out how much dark matter it has, astronomers needed to compare the mass of the matter we can see to the galaxy's total mass.
要弄清楚该星系里有多少暗物质，天文学家需要将我们能观测到的暗物质的质量与该星系的总质量进行比较。
They were able to determine DF2's stellar mass, or how much of its mass comes from stars, based on its brightness and distance.
他们可以判断出DF2的恒星质量，或者根据其亮度和距离来判断其中有多少质量是来自恒星的。
The team estimated that it's around 65 million light-years away,
据该小组估计，这个星系距离我们大概6500万光年的距离，
which produced a stellar mass of about 200 million times the mass of the Sun, which is roughly 250 times less than that of the Milky Way.
其恒星质量是太阳质量的近2亿倍，而银行系质量是它的近250倍。
Then they calculated the mass of the halo surrounding the galaxy, which should, theoretically, be chock full of dark matter.
然后，他们计算了该星系附近光晕的质量。理论上来讲，这部分光晕里应该充满了暗物质。
To do that, they measured the velocities of 10 different star clusters at distances between 1300 and 25,000 light-years from the center.
为了得出计算结果，他们测量了与中心距离在1300-25000光年之间的10个不同星团的速度。
Since a more massive galaxy will make stars orbit faster, they used those clusters' velocities to calculate the total mass for the whole galaxy.
星系质量越大，其恒星运行速度越快。基于这一点，他们通过这些星团的速度来计算整个星系的总质量。
Then they subtracted the stellar mass they'd already accounted for, which left them with the mass of the dark matter halo.
然后减去已经得知的恒星质量，得到的就是暗物质光晕的质量。
Which turned out to be less than 150 million times the mass of the Sun.
结果是：太阳质量是暗物质光晕质量的150倍。
Now, that's not zero dark matter, but current models say the number should be closer to 60 billion solar masses, 400 times more than what we're seeing!
现在可以得知该星系中含有暗物质，但当前的所有模型都告诉我们：这个结果被应该接近于太阳质量的600亿倍，是我们所得结果的400倍。
Since it's such a unique oddity, we still don't know how a dark matter deficient galaxy like DF2 came to be.
这种情况太过怪异，我们目前还不知道像DF2这样缺少暗物质的星系是如何形成存在的。
The team proposed a few ways it might have formed from regular matter that wouldn't have taken much dark matter with it.
该小组提出了几种该星系形成的方式，在这几种方式里，该星系都是从携带少量暗物质的常规物质中形成的。
For example, from gas that was flung out of merging galaxies, or that was streaming toward a neighboring galaxy but ended up splitting off.
比如，由一些星系形成过程中释放的气体所形成，或者从流向附近某星系过程中四散开来的气体所形成。
Until we find more galaxies like this one, it'll be tough to come up with a solid origin story.
在没找到与此类似的其他星系之前，很难盖棺定论。
But the discovery does help show that dark matter and baryonic matter are not inexorably linked to one another
但这次发现确实帮助我们明白：暗物质和重子物质并不是非要相生相伴的，
in other words, the amount of one does not determine the amount of the other.
换言之，他们任何一方的总量与对方的总量并无必然关系。
And, it helps put another nail in the coffin for hypotheses that dark matter isn't real,
此外，此次发现还助力击溃了暗物质并不存在的假说，
and that what we call dark matter is actually just our own physics equations being wrong.
证明暗物质其实只是物理方程的说法是错误的。
Because if that were the case, we wouldn't expect to find random galaxies with very little of it.
因为如果这种假说属实的话，上述那个暗物质含量极少的星系就根本不会存在。
As for when we'll finally pin down what exactly dark matter is, only time will tell.
那我们什么时候能搞清楚暗物质究竟为何物的问题呢？慢慢来吧。
Much closer to home, astronomers have finally solved a mystery involving a galactic tug of war and cannibalism on the outskirts of the Milky Way.
而在离我们更近的地方，天文学家终于解决了一个银河系边缘地区一场拉锯战和相互吞食的谜题。
The Large and Small Magellanic Clouds are irregular dwarf galaxies about 160,000 and 200,000 light-years from our own.
大小麦哲伦星云是分别距离银河系16万光年以及20万光年的不规则矮星系。
They both orbit the Milky Way, but as they do so, they also orbit one another.
这两个星云除了都围绕银河系运行之外，也围绕彼此运行。
The gravity involved in that system means that one of the Clouds has ripped away some of the other's gas,
由于这两个星云形成的小体系之间存在引力，所以其中一个星云会裹挟走另一个星云上的气体，
and sent it spiraling toward us in a fragmented arc roughly half the length of the Milky Way!
并将其裹挟走的气体以螺旋方式向我们跑过来，线路是间断性的弧形，长度占据了整个银河系的半壁江山！
The question is: which Cloud is siphoning gas away from the other?
问题是：哪个星云会吸取另一个星云上的气体呢？
That's been a mystery for some time now, although admittedly not as long as the arc has been around, since it's roughly 2 billion years old.
这个谜团已经存在一阵子了，我们是在这种现象出现的一段时间后才发现它的，毕竟这种现象已经存在了将近20亿年了。
Obviously we weren't around back then to ask these kinds of questions.
显然，那时候还没有人类，自然也就不会产生这样的谜团。
Thanks to a paper published last month in the Astrophysical Journal, we may finally have an answer.
不过，上个月《天体物理学杂志》上发表的一篇论文可能会解开我们的谜团。
Astronomers call this arc of gas the Leading Arm, because it's leading the motion of the Magellanic Clouds.
天文学家将这种气弧成为流前导臂，因为其引领着麦哲伦云的运动。
It kinda looks like this arm starts out in the Large Magellanic Cloud.
流前导臂有点像大麦哲伦星云里支出来的一部分。
But to confirm its real galactic parent, the team used the Hubble Space Telescope to analyze some of its composition, and compare it to both dwarf galaxies.
但为了确认其究竟是由银河系里的什么形成的，该小组通过哈勃望远镜分析了其组成，并将其与矮星系进行了对比。
Specifically, they looked at the light from seven quasars, incredibly bright cores of galaxies powered by supermassive black holes.
他们专门观测了7个类星体发出的光。所谓类星体就是由特大质量黑洞提供能量的星系的极为闪耀的内核。
Based on where they're each located in space, the light from these quasars had to travel through one of the Magellanic Clouds or the Leading Arm on its way to us.
根据它们各自的位置，这7个类星体发出的光在抵达地球之前会先经过麦哲伦星云或者流前导臂。
And depending on their composition, the molecules in the Clouds and Arm would have absorbed different wavelengths of the light as it passed through.
而根据其组成，麦哲伦星云或流前导臂中的分子在这个过程中会吸收不同波长的光。
By analyzing which types of light were absorbed, the team was able to match the Arm's composition with the Small Magellanic Cloud.
通过分析所吸收光的种类，该小组发现流前导臂的组成跟小麦哲星云相匹配。
Large Magellanic Cloud, you are not the father! Or mother.
大麦哲星云你想当长辈？不可能的！
But you did kind of gravitationally tear off part of your galactic partner and allow the Milky Way to cannibalize it and make new stars, so it's complicated.
不过，大麦哲星云还是通过引力的作用将小麦哲星云上的部分气体扯脱。随后，通过银河系的吞食，形成了一些小恒星，所以这个过程还是比较复杂的。
Of course solving this mystery wasn't just to satisfy curiosity.
当然了，解决这个谜题并不只是为了满足好奇心。
Understanding how gas falls or accretes into galaxies is an important step toward better models of how galaxies grow and evolve.
弄明白气体是如何流入或者说融合进各个星系中是非常关键的一步，可以让我们构建各星系形成发展方式的更加精良的模型。
But most galaxies are too far away for us to detect the light we'd need to study.
但大多数星系对于我们来说还是太过遥远，所以我们无法观测到研究所需的光线。
So the fact that we have an example of this galactic gas accretion right on our own front porch is a huge benefit.
所以我们现在有了这样一个银河系里气体吸收的例子，是非常有用的。
Between that and DF2's missing dark matter, we've got all kinds of galactic mysteries to solve!
在这个谜团和DF2消失的暗物质之间，我们依然有很多谜团有待解决！
Thanks for watching this episode of SciShow Space News! For more on galaxies with weird amounts of dark matter,
感谢您收看本期的《太空科学秀》！想要了解更多星系与暗物质有关的谜团的话，
you can check out our episode on Galaxy X, which is almost entirely made up of dark matter.
您可以观看我们与X星系有关的那一期，因为X星系几乎是完全由暗物质组成的。
