MRI: Acquisition of a Stable Hydrogen Maser Frequency Standard for mm/submm VLBI Observations of a Black Hole Event Horizon

天文学家探测遥远天体精细结构细节的能力取决于他们的望远镜和仪器所能获得的角度分辨率。角分辨率与进行观测的波长(波长越小，可达到的分辨率越高)有关，也与观测物镜的直径(物镜越大，分辨率越高)有关。在大多数情况下，观测对象是望远镜主镜的大小。但是，当同时使用多个望远镜并将它们的光束组合在一起时，物镜的大小就变成了所用望远镜之间的基线距离。几十年来，射电天文学家通过协调不同大陆上射电望远镜之间的观测，利用了一种名为甚长基线干涉测量(VLBI)的技术，从而利用了大基线。这项技术使射电天文学家(与可见光相比，他们在相当长的波长下工作)能够获得与光学天文学家可用的各种分辨率相媲美，在某些情况下甚至超过的角分辨率。现在，麻省理工学院干草堆天文台的Sheperd Doeleman博士希望通过将VLBI观测移动到更短的波长来获得更高的分辨率。他的想法将在一定程度上通过国家科学基金会重大研究仪器项目的奖励而成为可能，该奖项将使他能够获得一个非常稳定的高频标准，这是校准较短波长观测所必需的。这一新标准将使观测成为可能，从而更好地了解黑洞周围的环境，黑洞位于我们银河系的中心，距离我们超过2万光年。

The ability of astronomers to detect fine structure details in distant objects depends upon the angular resolution obtainable from their telescopes and instruments. Angular resolution is related to the wavelength at which the observations are made (the smaller the wavelength, the higher the resolution that can be achieved) and also to the diameter of the observing objective (the larger the objective, the higher the resolution). In most cases the observing objective is the size of the telescope's primary mirror. But when multiple telescopes are used simultaneously and their beams are combined the objective size becomes the baseline distance between the telescopes used. For several decades, radio astronomers have taken advantage of large baselines by coordinating observations between radio telescopes on different continents in a technique termed Very Long Baseline Interferometry (VLBI). This technique has enabled radio astronomers (who work at quite long wavelengths compared to that of visual light) to achieve angular resolutions that rival, and in some cases surpass, the kinds of resolutions available to optical astronomers. Now Dr. Sheperd Doeleman of the MIT Haystack Observatory wants to obtain even higher resolution by moving VLBI observations to shorter wavelengths. His idea will be made possible, in part, through an award from the National Science Foundation's Major Research Instrumentation program that will enable him to obtain a very stable high frequency standard that is necessary to calibrate the observations at the shorter wavelengths. This new standard will enable observations that will lead to a better understanding of the environment surrounding the Black Hole at the center of our Milky Way Galaxy, more than 20,000 light years away.