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.

尽管30年前，黑洞只是爱因斯坦一般相对论允许的假设对象，但我们现在有强有力的观察证据表明它们实际上存在于自然界中。我们可以获得的有关黑洞的信息主要来自其对光信号（包括光谱以外的信号）的影响，该信号靠近黑洞。在这个项目中，我们计划研究两种效果，不仅在真空中，而且在等离子体中的光传播与无线电信号相关。 （a）首先，我们想计算从旋转黑洞的脉冲星的信号旅行时间。与早期对此问题的研究相反，我们希望考虑到围绕黑洞的不均匀等离子体的影响。 （b）其次，我们要考虑（小但扩展的）源的光，该光源绕着黑洞旋转并在其休息框架中发射。光源可以解释为积聚光盘中的热点。 特别是，我们要考虑以下情况：光源在其轴上旋转，并且要考虑旋转对发射辐射的影响。在真空中进行光传播之后，我们还希望考虑不均匀的等离子体的影响。这具有有趣的应用，即使对于源是非旋转的情况下，也可以通过围绕黑色孔进行辐射旋转盘进行建模，因为由许多绕线光源组成，可以计算血浆对这种圆盘视觉外观的影响。在所有情况下，我们的目标是尽可能地得出精确的分析公式，并使用分析性辅助方法。黑洞主要由Schwarzschild或Kerr Spacetime建模，但是其他指标（替代理论的黑洞和诸如虫洞之类的黑洞的黑洞）也将部分包括在研究中。该项目的主要动机来自已经存在或预期的（超大或恒星）黑洞的观察结果。分析公式对血浆对绕光源发射的辐射的影响的影响将是评估这些观察结果并正确解释它们的重要工具。