Relativistic jets from accreting black holes: are they baryonic or leptonic?

相对论外流通常与吸积成致密物体有关，特别是黑洞。这些流出是平行的，以喷流的形式出现。这些喷气式飞机是如何发射的，这是一个挑战天体物理学数十年的解决问题。也几乎不知道喷气式飞机里到底有什么。在大多数研究中，喷流被建模为电子-质子等离子体的磁流体流。然而，也有研究认为，来自吸积黑洞的相对论喷流是轻子的，即它们是电子-正电子等离子体流。无论喷流是重子的还是轻子的，喷流物质中的高能含量以及与喷流中的相对论流动相关的剧烈现象，如喷流与周围块状物质的冲击和卷吸，都会产生正电子对。这些配对将会印记观测签名。这些信号将对喷流中的相对论流动动力学和物理条件，以及喷流如何与环境相互作用提供有用的诊断。相对论喷流中的对产生还没有得到充分的探索，特别是在喷流-环境相互作用和重子/轻子混合背景下。在这个项目中，学生将建立发生对产生的结构化喷流模型，并计算相关的辐射过程。这是一项涉及唯象建模、解析计算和数值计算的理论工程。其目的是得出可通过目前或未来的X射线/伽马射线/射电观测来检验的预测，并提供适用于天体物理学其他分支的有用工作模型，例如涉及宇宙射线和中微子的天体粒子物理学。

Relativistic outflows are often associated with accreting into compact objects, in particular, black holes. These outflows are collimated, in the form of jets. How these jets are launched is an resolved issue that challenge astrophysics for decades. Little is also know what exactly are in the jets. In most studies the jets are modeled as magneto-hydrodynamical flows of electron-proton plasmas. However, there are also studies which argue that relativistic jets from accreting black holes are leptonic, i.e. they are electron-positron plasmas flows. Regardless of whether the jets are baryonic or leptonic, the high-energy contents in the jet material and the violent phenomena associated withe relativistic flows in jets, such as shocks and entrainment of the jets with the clumpy ambient material would give rise to electron-positron pair production. These pairs would imprint observational signatures. These signatures would provide useful diagnostics of the relativistic flow dynamics and the physical conditions in the jets, as well as how the jets are interacting with their environments. Pair production in relativistic jets has not been fully explored, especially in the context of jet-environment interaction and in the hybrid baryonic/leptonic settings.In the project, the student will develop structured jet models in which pair-production occur and calculate the associated radiative processes. It is a theoretical project, which involves phenomenological modeling, analytical calculations and numerical computation. It aims to derive predictions that can be tested by current or future X-ray/gamma-ray/radio observations and to provide useful working models that are applicable in other branches of astrophysics, e.g. astro-particle physics involving UHE cosmic rays and neutrinos.