【视频】（科学声音配音）EHT 官方公布的黑洞拍摄原理

朝着黑洞落下的气体会被加热到数十亿度的高温causing the event horizon to appear as a silhouette使得事件视界看上去就像是“剪影”whose size and shape are predicted by Einstein’s theory.爱因斯坦的理论能预测这个剪影的尺寸和形状It is best to observe the silhouette in light with a wavelength of about one millimeter观测剪影的最佳波长约为1 毫米where the gas glows most brightly气体在这个波段辐射最明亮and light can travel unimpeded from the center of the galaxy to telescopes on earth.而且毫米波也可以从银河系的中心直达地球的望远镜Close to the black hole, the light waves appear circular like ripples in a pond接近黑洞时光波看上去就像是池塘里的圆形涟漪but by the time they reach earth they're essentially plain waves.但当它们抵达地球时基本上已经是平面状的了Imaging a black hole at this wavelength requires a telescope as big as our planet.为这样的黑洞成像需要口径像地球一样大的望远镜The EHT uses a global network of dishes to simulate a telescope of this size.EHT 利用世界不同地点的射电望远镜来模拟这个效果Each dish collects and records每一台射电望远镜都收集并记录radio waves coming from near the black hole.来自黑洞附近的无线电波信号The data are then combined to create the image of the event horizon.这些数据集合起来构成了事件视界的图像This will only work however, if the dishes are completely synchronized.计划要成功就需要所有的射电望远镜都在时间上同步To understand this,为了帮助你理解let's use the analogy of a mirror such as an optical telescope used for star gazing.我们用光学望远镜的镜面来作比喻Imagine the EHT formed from all the different arrays sites想象一下全球各地的望远镜组成的EHT 网络as one big parabolic mirror.是一个巨大的抛物面镜The mirror is curved镜面有一些弧度so that when a line of waves comes into the dish,当平行光进入盘面时they bounce off at specific angles and arrive at the focus at the same time.会在特定的角度反射并同时到达焦点When the EHT sites are synchronized,当EHT 的每个观测点都在时间上同步时their recordings can later be perfectly aligned它们的观测数据随后就能得到完美的修正in the same way that the mirror aligns the optical light.这与利用镜面修正收集到可见光的方法相同If the surface of the mirror is not stable,如果镜子的表面不稳定if it is vibrating for example,比如说振动the reflected light rays will not combine properly at the focus.反射光就无法完美聚焦For the EHT,对EHT 而言an unstable mirror surface is analogous to an unstable recording.不稳定的信号就如同不稳定的镜面To ensure stability,为了保证稳定性the EHT uses atomic clocks that would lose only one second every hundred million years.EHT使用了每一百万年只会误差1 秒的原子钟The amount of data recorded during observations is so large因为观测期间记录到的数据过于庞大that it could never be transferred over the Internet.所以不可能通过网络传输Instead, the recordings are stored on hard disksEHT 的数据被记录在硬盘上and shift back to a central facility for processing.这些硬盘寄回数据中心后再进行处理There, a super computer combines the data from all the sites,在那里一台超大型计算机负责汇总来自所有地点的数据staggering them during playback to account for the time difference between waves getting to each telescope.矫正数据抵消光波到达每个望远镜的时间差The resulting data can then be used to make images with extreme magnifying power得到的数据可以用来制作放大率极佳的影像As more dishes join the EHT and the more widely spaced they are,随着加入EHT 的射电望远镜数量越来越多、分布越来越广the sharper our image of the event horizon will be.事件视界的图片也将变得越清晰