Staring into the abyss
凝望深渊
Astronomers take the first snap of a black hole
天文学家首次拍到黑洞照片
What black holes do to the things around them is hard to miss. Matter hurtling into them at almost the speed of light gives off all sorts of radiation, sometimes so much of it that it can be seen half a cosmos away. The black holes themselves, though, are another matter. They are, by cosmic standards, extremely small. And they are defined by having gravitational fields so strong that nothing, not even light, can escape them. That is why it is remarkable that an international team of more than 200 radio astronomers have, through years of painstaking work, actually contrived a glimpse of one.
黑洞对于周边物质的影响值得人们去关注。被黑洞吸入后，物质开始以近似于光的速度猛冲，并散发出各类辐射光线，有时辐射量过大，在半个宇宙之外都可以看见。然而，黑洞本身就是另一种物质。从时空标准来看，黑洞是极其微小的一种物质。同时从科学界的定义来看，黑洞由于拥有极强的引力场，所有物质，甚至是光都不能逃过黑洞引力的捕获。这就是这张黑洞照片意义非凡的原因所在，它的背后是超过200名来自世界各地科学家的不懈努力，他们多年来辛勤工作才为人类呈现了这惊人的一瞥。
The black hole in question (pictured below) is located at the centre of a galaxy 55m light-years from Earth called Messier 87, one of the largest and most luminous galaxies in the nearby universe. Astronomers have for some time suspected that it houses a phenomenally massive black hole—one 6.5bn times more massive than the Sun, and more than a thousand times more massive than the black hole at the centre of the Milky Way galaxy in which the Earth and Sun sit.
这幅照片中的黑洞位于一星系的中心，距离地球5500万光年，这一黑洞所处的星系名叫麦瑟尔87（Messier 87），它是地球附近宇宙中最大也是光度最高的星系。长期以来，天文学家都怀疑这一星系是否存在一个极其庞大的黑洞，科学家推测，这个黑洞的重量是太阳的650亿倍，它比银河系中心（太阳和地球位于的星系）的那个黑洞重至少1000倍。
But massive does not mean large. The edge of a black hole is called an event horizon, because nothing that happens beyond it can ever be seen under any circumstances. The black hole in Messier 87 has an event about half a light-day across (about the size of the bit of the Solar System that has planets in it). This means that, seen from the Earth, it looks no larger than a coin on the surface of the Moon.
但黑洞的庞大并不意味着其真正的体积很大。黑洞的边缘被称为“视界线”，它是黑洞的边界，在此边界以内的任何物质在任何条件下都无法逃离。麦瑟尔87的这个黑洞拥有一个宽达半个“光日”的视界线，这一宽度和太阳系行星占据的体积相差无几，这就意味着，若从地球上观察这个黑洞，它还没有月球表面一枚硬币那么大。
The smaller the thing you are observing appears in the sky, the larger the aperture of the telescope you need to look for it. The Event Horizon Telescope (eht) team put together one with an aperture the size of Earth by bringing together data from radio telescopes all around the world. Adding together the signals received by these various telescopes allowed them to synthesize an image as good as the one they would have got from single telescopes as large as the distance between any two of the dishes, though a great deal dimmer. This sort of “extremely long baseline interferometry” has been used for decades—but never before with this amount of data.
如果你想在天空中观测到更微小的星体，你就需要孔径更大的望远镜。视界线望远镜（EHT）这一研究团队在射电望远镜收集到的数据基础上，打造了一台孔径达到地球大小的望远镜。同时，EHT依靠多台分散式望远镜，将它们接收到的信号整合起来，最终合成了黑洞照片，并且这张照片的成像质量和单一望远镜观测的照片基本一样，只不过亮度要低一点。这种所谓的“超长基线干涉量度分析法”已被科学家使用了几十年了，但从未涉及到这么大规模的数据处理。
In total, eight observatories on four continents were used to hunt for the black hole in Messier 87, including two, in Antarctica and Chile, that enjoy particularly dry skies. Because the observations needed to be precisely synchronized, each instrument was tethered to its own atomic clock. Once all the dishes were properly configured, the astronomers calculated they required ten days of clear weather in all the locations to collect the data that were needed. When they began their search in April 2017 the weather behaved, and they got five petabytes of data in seven days. These data were transported to the Haystack Observatory at the Massachusetts Institute of Technology in America and the Max Planck Institute for Radio Astronomy in Bonn, Germany, on half a ton of hard drives.
为了追踪麦瑟尔87的这个黑洞，科学们利用了分散在4大洲的共8座天文台，尤其是位于南极洲和智利的两台，它们所处的干燥气候十分适合这次行动。由于观测行为必须精确同步，每一台设备都安装了原子钟以确保同步性。如果所有机器的天线都调试妥当，天文学家就可以开始收集以及计算数据了，这一过程需要持续十天，并且要求所有参与行动的天文台附近的天气都保持晴朗。最终，这些数据都被传送到了位于美国的麻省理工学院和位于德国波恩的无线电航空学院。值得注意的是，装载这些数据的硬盘重达半吨。
These many numbers underwent much crunching. On April 10th the result was revealed. The first real picture of a black hole, which looks satisfyingly black and blobby, consists of radiation emitted by hot gases on the far side of the black hole and then bent by its gravity into a tube of light with darkness in its central cavity. The brighter yellow at the base of the circle indicates gases moving particularly quickly, hinting at a something of a slingshot effect taking place as the vortex of gases travel in a clock- wise direction, much like water pouring down a plug hole.
科学家对这些大规模数据进行了大量的处理和运算，在4月10日，相关组织公布了研究结果，包括首张黑洞照片。照片中的黑洞看起来的确很黑，形状难以名状，它包括从黑洞远端热气体散发出的强光，由于引力的作用，光线被压弯成管腔状，并且管腔中部呈现出暗色。这一圆环基部的明黄色表明周围气体的运行速度非常快，当气体的漩涡沿顺时钟方向运动时，也意味着着某种弹弓效应的发生，就像水从塞孔中倾泻而下一样。
In time, the same approach should be able to track changes in the environment around this black hole and others, helping to show, among other things, how the vast jets of energy it emits get their oomph and structure. In the meantime, there are two important take away messages. One is that black holes are round, as Einstein’s theory of relativity predicted they would be. The world is used to Einstein being proved right; but each test that might contradict him and doesn’t is an event.
随着时间的推移，相同的方法就能够用于追踪这个黑洞和其他黑洞周围环境的变化，这有助于揭示它所释放的巨大能量喷流是如何获得推力和结构的。同时，这里得补充两个非常重要但十分简单的信息。首先，爱因斯坦的相对论预测黑洞是圆的，结果证明他是对的，当然人类已经对爱因斯坦的正确性习以为常了，同时他对于视界线的预测也被证明是正确的。
The other is that if they see a possibility fascinating and spectacular enough, astronomers will be remarkably dogged in its pursuit, even using the whole moving Earth to plumb the heavens.
其次，如果天文学家从此看到了探索黑洞的可能性，他们就会更加坚持这样的科学研究，甚至可能利用整个移动的地球来进行太空探测。
