Propagation of light signals near a black hole surrounded by a plasma

被等离子体包围的黑洞附近光信号的传播

• 批准号: 429796200
• 负责人: Professor Dr. Claus Lämmerzahl
• 金额: --
• 依托单位: Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation (ZARM)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/429796200?language=en
• 关键词: Propagation; light; signals; near; black

Whereas 30 years ago black holes were just hypothetical objects allowed by Einstein's theory of general relativity, we have now strong observational evidence that they actually exist in Nature. The information we can get about a black hole comes mainly from its effects on light signals (including signals beyond the optical spectrum) that come close to the black hole. In this project we are planning to investigate two such effects, considering light propagation not only in vacuo but also in a plasma which is of relevance for radio signals. (a) Firstly we want to calculate the travel times of signals from a pulsar that orbits a black hole. In contrast to earlier studies of this problem we want to take the effects of an inhomogeneous plasma into account that surrounds the black hole. (b) Secondly we want to consider light from a (small but extended) source that orbits a black hole and emits isotropically in its rest frame. The light source may be interpreted as a hot spot in an accretion disc. In particular, we want to consider the case that the light source is spinning about its axis and the influence of the spin on the emitted radiation is to be taken into account. After doing this for light propagation in a vacuum, we also want to take the effects of an inhomogeneous plasma into account. This has interesting applications, even for the case that the source is non-spinning: Modelling a radiating rotating disc around a black hole as consisting of many orbiting light sources allows to calculate the influence of a plasma on the visual appearance of such a disc. In all cases, it is our goal to derive exact analytical formulas as far as possible and to use analytical apporoximation methods otherwise. The black hole is mainly to be modelled by the Schwarzschild or the Kerr spacetime, but other metrics (black holes of alternative theories and black hole impostors like wormholes) will be partly included in the investigation as well. A main motivation for this project comes from already existing or expectable observations of (supermassive or stellar) black holes. Analytic formulas for the influence of a plasma on the radiation emitted by orbiting light sources would be important tools for evaluating these observations and interpreting them correctly.

三十年前，黑洞只是爱因斯坦广义相对论所允许的假设物体，而现在我们有强有力的观测证据表明它们确实存在于自然界中。我们能够获得的关于黑洞的信息主要来自于它对靠近黑洞的光信号（包括超出光谱的信号）的影响。在这个项目中，我们计划研究两种这样的效应，不仅考虑真空中的光传播，还考虑与无线电信号相关的等离子体中的光传播。 (a) 首先，我们要计算来自绕黑洞运行的脉冲星的信号的传播时间。与早期对该问题的研究相反，我们希望考虑黑洞周围不均匀等离子体的影响。 (b) 其次，我们要考虑来自（小但扩展的）光源的光，该光源绕黑洞运行并在其静止坐标系中各向同性发射。光源可以被解释为吸积盘中的热点。 特别是，我们要考虑光源绕其轴旋转的情况，并且要考虑旋转对发射辐射的影响。在对真空中的光传播进行此操作之后，我们还想考虑不均匀等离子体的影响。即使对于源不旋转的情况，这也有有趣的应用：将黑洞周围的辐射旋转圆盘建模为由许多轨道光源组成，可以计算等离子体对此类圆盘视觉外观的影响。在所有情况下，我们的目标是尽可能推导出精确的解析公式，否则使用解析近似方法。黑洞主要通过史瓦西或克尔时空来建模，但其他指标（替代理论的黑洞和虫洞等黑洞冒充者）也将部分包含在调查中。该项目的主要动机来自对（超大质量或恒星）黑洞的现有或预期观测。等离子体对轨道光源发射的辐射影响的解析公式将是评估这些观察结果并正确解释它们的重要工具。