时空胶囊 - 上篇 Time Capsules Part 1
矮星系，虽然比我们的银河系小几百倍，被许多人认为是我们宇宙的时空胶囊。它们是宇宙中最盛产的星系类型，经常在伴随其他较大星系，在星系团中被发现。
Dwarf galaxy, although a few hundred times smaller than our Milky Way, are believed to be time capsules of our universe. They are the most abundant type of galaxy in the universe are often found in galaxy clusters accompanying other larger ones.
图为NASA哈勃望远镜拍到的一个叫NGC 5949的矮星系，它离我们的距离大约是4400万光年
A dwarf galaxy from NASA's Hubble names NGC 5949, it is ~ 44 million light years away from us
被称为时空胶囊的原因是他们被可能包含了早期宇宙的黑洞种子。在银河系附近，大部分被探测到的矮星系与它们周围的邻居没有太多的交流。因此可以认为，矮星系们基本都会将自己孤立在它们那一小团团气体、尘埃和恒星，独自进化。
Instead of being old records, reason for being described as time capsules is that they are believed to contain the seeds black holes in the early universe. Most nearby dwarf galaxies detected are found to be not interacting much with their surrounding neighbours, any therefore isolating themselves to their little collection of gas, dust and stars, evolving on their own.
因为没有自他人的污染，它们成为科学家研究早期宇宙的理想干净样本。看，即使是星系们也有自己的新冠病毒，要记得时刻保持距离哦。
Without the contaminations from others, they become the ideal clean sample pockets for the scientist to study early universe. See? Even stars can have their own COVID.
通过分析这些矮星系中黑洞的分布和质量，我们有机会找到它们最初是怎样形成的。不仅仅是在矮星系中，答案也可以用在宇宙中的所有星系上。
By analyzing the distribution and masses of the black holes in these dwarf galaxies, it may be possible to find how they were formed in the first place. Not just in these galaxies, but all of them around the universe.
图为人类用视界望远镜拍到的第一张黑洞照片，它位于M87星系的中心，是太阳质量的65亿倍
The first image of a black hole taken by human using the Event Horizon Telescope, it is located at the centre of the M87 galaxy, and is 65 billion times the solar mass
探洞三部曲 之 前奏
The Black Hole Trilogy - Intro
科学家们普遍认为黑洞形成的主要机制有两种。其一，它们可能是由早期恒星的坍缩形成的，也被称为III型恒星(详情请看附属文章)。另一种可能是气体和尘埃的直接坍塌。这两个结果的不同之处在于，恒星的坍缩相比气体和尘埃的坍缩会产生更多的低质量黑洞。
There are two main mechanism theories that scientists think are possible for the black hole formation. One being, they can be formed from the collapse of early generation stars, also known as the Population III (for more info, please see attached article). Or another possible way is simply the direct collapse of gas and dust. The difference in results that are aimed to detect is that the collapse from stars would produce much more low mass black holes than just collapse of gas and dust.
遗憾的是，由于矮星系的亮度、质量和大小都比附近的耀眼的星系要低，它们变得很难被探测到。而基本隐形的黑洞们更是让观测他们变得更具挑战。
Unfortunately, due to their lower luminosity, mass and size compared to their glamorous neighboring galaxies, they become very difficult to detect. The often-invisible black holes provide an even more challenging task.
但是，有了活跃星系核(AGN)的活动数据，看不见他们的问题就可以迎刃而解啦。活跃星系核(AGN)经常会聚集大量物质并释放大量的辐射，它们可以被理解为黑洞。AGN在上一篇关于大质量静止星系的文章中也提到过，在静止星系中它们可以显著地增加大星系的演化。所以，AGN的存在还是很重要的哦。
However, a solution can be found by the using the activity data from the active galactic nucleus (AGN), which accrete material and emit huge amounts of radiation every so often, they can be understood as black holes. AGN were also mention in the last article on the massive quiescent galaxies, in which they can dramatically increase the evolution of large galaxies.
图为NASA哈勃望远镜拍到的 NGC 7742星系，它是一个赛弗特2活跃星系，一种可能由其核心黑洞提供能量的星系
The NGC 7742 galaxy from NASA's Hubble, it is a Seyfert 2 active galaxy, which is a type of galaxy that is most likely to be powered by its black hole in the core
正巧，在最近几十年里，对矮星系中AGN的探测已经有了很大的增长。因此，一个来自耶鲁大学和蒙大拿州立大学的小组开始了对AGN和对矮星系的新研究。他们目标是将这些AGN与天体质量和速度(M-σ)色散关系进行对比，并深入了解早期宇宙中黑洞是如何形成的。M-σ色散关系指的是星系速度与其黑洞质量之间的经验相关性。
With that said, there has been a huge increase in the detection of AGNs in dwarf galaxies in the last few decades. So, a group from Yale University and Montana State University has joined up, aiming to compare some of these AGNs to the stellar mass & velocity (M-σ) dispersion relation, which is an empirical correlation between velocity of galaxies and the mass of its black hole; and gain some insight into how black holes may have formed in the early Universe.
探洞三部曲 之 质量
The Black Hole Trilogy - Mass
用于寻找合适样本的数据来自NASA-Sloan Atlas，它是一个专门用紫外线、可见光或近红外研究附近星系的卫星探测仪。得到数据后，研究小组使用BPT判断法(Baldwin, Phillips & Terlevich的名字命名的判断方式)来识别任何数据组中的AGN。
The data used for finding the suitable sample group was from the NASA-Sloan Atlas, which specialise in surveys in the UV, optical or near-infrared on the local galaxies. The group then used the BPT diagnostic (named after its creators Baldwin, Phillips & Terlevich) to identify any AGNs.
图为NASA-Sloan Atlas的 NGC 4395矮星系，它是研究小组进行筛选后的八个样本之一
A dwarf galaxy named NGC 4395 from NASA-Sloan Atlas, it's one of the eight from the sample set the team selected
方法是，通过比较两对光发射线的比值后，确定光谱主要是来自星系中的AGN，还是星系中的恒星，还是两者都有。此外，还要求星系具有近Hα发射谱线 (巴耳末线系中的深红可见谱线 —— 氢原子发射谱线系的一部分)，这样就可以计算出它们黑洞的维里质量了。
The technique was to compare the ratio of two optical emission line pairs to determine whether the spectrum mainly originated from the AGN process in the galaxy or star formation or a composition of both. Furthermore, the galaxies are also required to have broad Hα emission line (specific deep-red visible spectral line in the Balmer series – a series of spectral emission lines of the hydrogen atom) so their virial mass of the black hole can be calculated.
需要知道光谱是因为，它还可以提供了AGN星系的宽线区(BLR)的细节。BLR在星系里是一个高度电离的内部区域，因此通过了解星系宽的光度和Hα最大值，我们可以得到该区域内物质的大小和速度信息。然后所有这些数据将用于计算黑洞质量。
The spectrum also gives details on the broad line region (BLR) in the galaxy with AGNs. BLR is a highly ionised inner region, so by knowing the luminosity and full-width half-maximum of galaxy’s broad-line Hα, we can have information on the radius and velocity of material in that region. All those data are then used in calculation of the black hole masses.
根据上述标准，本组从原始数据集中筛选出了8个合适的对象，并且均具有所需Hα值, 以及BPT判断出的AGN或恒星混合AGN发光体。
With the criteria above, the group identified 8 suitable objects from the original data set, all with the required broad-line Hα while classifies by the BPT diagnostic as Composite or AGN.
了解了这些矮星系的质量，
接下来就是计算他们的速度啦！
敬请期待《时空胶囊 - 下篇》
揭晓黑洞形成更多奥秘！
Knowing the masses of these dwarf galaxies,
the next step is to calculate their velocities.
Stay tuned for next part of
"The Time Capsule"
to reveal more mysteries of
black hole formation!
图为NASA-Sloan Atlas的 NGC 205 矮星系，它是研究小组进行筛选后的八个样本之一
A dwarf galaxy named NGC 205 from NASA-Sloan Atlas, it's one of the eight from the sample set the team selected
图片来自 NASA-Sloan Atlas, NASA官网
部分信息参考来自耶鲁大学和蒙大拿州立大学的V F Baldassare, C Dickey, M Geha 和 A E Reines
的 “POPULATING THE LOW-MASS END OF THE MBH − σ∗ RELATION" 论文
Pictures from official website of NASA-Sloan Atlas, NASA.
*Parts are from “POPULATING THE LOW-MASS END OF THE MBH − σ∗ RELATION" by V F Baldassare, C Dickey, M Geha and A E Reines from Yale University and Montana State University
