Variability of Polarization and Intensity as Probes of the Accretion Flow of Sgr A*

我们银河系的中心有一个超大质量黑洞，被称为人马座a *。黑洞的质量是太阳的四百万倍。它最初是通过在它附近运行的热气体的无线电发射而被发现的。黑洞区域的亮度每小时变化一次。射电天文学家在过去的十年里观察到了这种变化。这个项目的目标是利用现有的数据来观察黑洞的特性。研究人员将研究黑洞附近亮度变化的物质流动。一个重要的目标是测量黑洞的旋转方向，并将其与整个银河系的旋转方向进行比较。该分析将通过模拟过去10年黑洞的变化来测量旋转轴。这位研究者已经在西北大学的主图书馆发起了两次关于射电天文学的公开展览。本次展览将重点关注射电天文学在我们日常生活中的影响，全球射电望远镜的多样性，以及详细的射电图像的艺术方面。研究者主要关注与Sgr A*变异性相关的三个主题。一是研究Sgr A*光厚变发射的磁场取向。这个角度与吸积流的自转轴和大尺度喷流的特征有什么关系？为了解决这一问题，将对绝热膨胀同步加速器热点进行全斯托克斯分析。二是对美国国家科学基金会甚大阵列（VLA）和阿塔卡马大型毫米波/亚毫米波阵列（ALMA）同步观测数据进行建模，应用绝热膨胀模型表征Sgr A*的内在变异性。利用Sgr A*的光学、红外和射电光曲线，研究人员将确定多个耀斑的亚毫米/无线电频谱和发射变异性。第三，VLA在过去十年中收集的VLA档案数据将用于解决比小时更长的时间尺度上的变率性质。这项研究将在长达十年的时间尺度上确定潜在变异性统计的动态，以确定热点的物理参数是否随时间而变化，从而为吸积流的历史提供信息。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The center of our Milky Way Galaxy hosts a supermassive black hole, known as Sgr A*. The black hole is 4 million times the mass of the Sun. It was first identified by radio emission from hot gas orbiting near it. The brightness of the black hole regions changes on hourly time scales. Radio astronomers have observed this variability for the last ten years. The goal of this project is to use available data to look at the properties of the black hole. The investigator will study the flow of material near the black hole where its brightness changes. An important goal is measuring the direction the black hole rotates and comparing it with the rotation direction of the entire Milky Way. The analysis will measure the rotation axis by modeling the changes in the black hole over the past 10 years. The investigator has initiated two public exhibits on radio astronomy at Northwestern's main library. This exhibit will focus on the impact of radio astronomy in our daily lives, the diversity of radio telescopes throughout the globe, and artistic aspects of detailed radio images.The investigator focuses on three topics related to the variability of Sgr A*. One is to address the magnetic field orientation of optically thick variable emission from Sgr A*. How does this angle relate to the spin axis of the accretion flow and the large-scale jet-like feature. To address this issue, full-Stokes analyses of adiabatically-expanding synchrotron hotspot will be carried out. Second is to model simultaneous observations from NSF’s Very Large Array (VLA) and Atacama Large Millimeter/Submillimeter Array (ALMA), to characterize the intrinsic variability of Sgr A* by applying the adiabatic expansion model. Using optical, infrared and radio light curves of Sgr A* the investigator will determine the submm/radio spectrum and emission variability across multiple flares. Third, archival VLA data taken with the VLA over the last ten years will be used to address the nature of variability on longer-than-hourly time scales. This study will determine the dynamics of the underlying variability statistics on timescales up to a decade, in order to determine if the physical parameters of hotspots have changed with time, informing the history of the accretion flow.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.