Collaborative Research: Building an Event Horizon Telescope: (Sub)millimeter VLBI from the South Pole Telescope

目前人们非常感兴趣的一个研究课题是位于银河系中心的超大质量黑洞，其质量约为400万太阳质量。类似的天体在其他星系中也很常见。我们对银河系这个奇异天体的了解大多来自于对受其强大引力场影响的恒星运动学的研究。到目前为止，还不可能直接成像黑洞，或者更确切地说，它的事件视界是引力的“不归点”，没有任何粒子或光子可以从中逃脱黑洞。银河系中心区域距离遥远，大约8kpc，这使得通过任何直接技术获得超大质量黑洞的高空间分辨率图像非常困难。如果能够获得这样的图像，它们将是同类图像中的第一个，并且可以揭示关于黑洞和星系核心动力学的尚未想象的信息。为了解决这一具有挑战性的科学问题。亚利桑那大学的D. Marrone、东北射电观测公司的S. Doeleman和芝加哥大学的J. Carlstrom打算改进现有的射电望远镜阵列，这些望远镜工作在最高的无线电频率（亚毫米，波长略短于一毫米）上，并采用一种模式，即由大陆基线分隔的望远镜将它们的数据连贯地组合在一起，以达到前所未有的空间分辨率。一般的技术被称为甚长基线干涉测量法，或VLBI，而使用的特殊射电望远镜阵列被称为事件视界望远镜（EHT），部分是通过NSF先前的奖励开发的。通过一项新的NSF提案，研究人员计划将南极望远镜（SPT）作为EHT的一个新站点。以这种方式增加观测站（望远镜）提高了对无线电信号的灵敏度，也提高了仪器作为成像设备的空间响应，这样就可以用较暗的物体绘制出质量更好的地图。除了增加一个关键观测站外，该技术还将采用一个新的、灵敏的双频毫米波VLBI接收器，该接收器将采用由国家射电天文台（NRAO）为阿塔卡马大型毫米波阵列（ALMA）项目开发的超导混频器技术，以满足该项目的需求。最后，经过验证的230 GHz设计将适用于345 GHz。这项工作的资金由美国国家科学基金会天文科学部通过其先进技术和仪器项目提供。

A research topic of great current interest is the supermassive black hole of about 4 million solar masses that is now known to exist at the center of our Milky Way galaxy. Similar objects are common in other galaxies. Most of what is known about the Milky Way's exotic object comes from studies of the kinematics of stars influenced by its strong gravitational field. No possibility has heretofore existed for directly imaging the black hole, or more technically its event horizon, the gravitational "point of no return" from within which no particle or photon can escape the black hole. The galactic center region is distant, about 8 kpc, making it extraordinarily difficult to obtain high-spatial-resolution images of the supermassive black hole by any direct technique. If such images could be obtained, they would be the very first of their kind, and could reveal information not yet imagined about black holes and the dynamics in the cores of galaxies. To attack this challenging scientific problem, Drs. D. Marrone of the University of Arizona, S. Doeleman of the Northeast Radio Observatory Corporation, and J. Carlstrom of the University of Chicago intend to enhance an existing array of radio telescopes operating at the very highest radio frequencies (the submillimeter, with wavelengths somewhat shorter than a millimeter) and in a mode where telescopes separated by continental baselines coherently combine their data to achieve unprecedented spatial resolution. The general technique is termed Very Long Baseline Interferometry, or VLBI, and the particular array of radio telescopes to be used is referred to as the Event Horizon Telescope (EHT), developed in part through a previous award from NSF. Through a new NSF proposal the researchers plan to add the South Pole Telescope (SPT) as a new station to the EHT. Adding stations (telescopes) in this manner enhances sensitivity to radio signals and also improves the spatial response of the instrument as an imaging device, so that better-quality maps may be made of fainter objects. In addition to the addition of a key observing station, the technology will feature a new, sensitive dual-band millimeter-wave VLBI receiver, optimized for the needs of this project, that will employ superconducting mixer technology developed for the Atacama Large Millimeter Array (ALMA) project by the National Radio Astronomy Observatory (NRAO). Finally, the proven 230 GHz design will be adapted for use at 345 GHz.Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.