Loading...
Showers and Shocks: Lepton Cascades Around Kerr Black Holes and The Weibel-Mediated Multi-Instability System
Sitarz, Michael Charles
Sitarz, Michael Charles
Citations
Altmetric:
Abstract
Plasma is the most common form of matter seen in the universe. It exists in planetary atmospheres, comprises the bulk of stellar bodies, can be seen in media between galaxies and nebula, and is a byproduct of many high energy astrophysical events. Understanding plasma and its processes can be as simple as using the Lorentz force and classical electrodynamics or as complicated as non-ideal magnetohydrodynamics with complex and dynamical terms in the system of many equations. Particles in plasma can even collide if the system allows it. While somewhat simpler in its existence, the collective behavior non-collisional plasma exhibits is one of the most interesting and important avenues of research in modern day extreme astrophysics. Collisionless plasmas play host to a multitude of physical phenomenon like pair production and annihilation, complex instabilities, oscillations and electromagnetic waves, and even collisionless plasma heating. This work studies collisionless pair-plasmas in two of the most extreme settings: Kerr Black Holes and relativistic shock waves.Plasma not only exists in some of the most extreme environments in astrophysics, but can be a crucial and necessary component for many settings. High magnetic fields drive the processes seen in these environments, inducing the particle cascades that fuel the high energy jets seen at the poles of supermassive, rapidly rotating black holes. The Blandford-Zjanek mechanism of transforming rotational energy into electromagnetic energy through an incoming photon bath originating from an accretion disk. An updated photon flux model motivated by state-of-the-art simulations is examined and the effects it has on the electron-positron cascade in plasma ``spark-gap'' region is studied. This new model more accurately depicts Milky Way like scenarios (Sgr A*), hot and dense accretions disks (both near and far), and disks with little to no material.Magnetic fields are not just an ingredient to plasma processes, but in many cases, the byproduct. High energy events such as supernovae blast waves and $\gamma$-ray bursts produce relativistic discontinuities (shock waves) in the plasma ejected and present around the explosive event. The Weibel instability is known to mediate various processes within this shock wave. It is also known to be the source of intense, randomly oriented magnetic fields seen in observations of these events. This body of work examines the environment the instability exists in through simulations of counter propagating beams. This work puts forth a parameterization of the system and its subsequent evolution as a result of different initial conditions such as skin depth, number density, and shock wave propagation velocity. Collective behavior is also studied. The various electromagnetic and electrostatic modes present in the system are viewed through a spectral cone technique. The interaction between particles and plasma waves is discussed as a possible acceleration and radiation mechanism for particles. Finally, collisionless heating and the resultant dynamical energy transformation is shown to be a valid consequence of violent filament merger in the Weibel mediated system. These studies put forth new evolutionary tracks based on initial conditions which include secondary excited instabilities. Within these tracks, possible solutions to the electron injection problem in Weibel mediated shocks are put forth through violent filament mergers. These mergers are the source of collisionless heating and particle-wave interactions that can accelerate particles into participating in diffusive shock acceleration.
Description
Date
2024-01-01
Journal Title
Journal ISSN
Volume Title
Publisher
University of Kansas
Collections
Archive Status
This item contains archived web content.
Files
1076810_1.pdf
Adobe PDF, 8.08 MB
- Embargoed until 2174-05-31
Research Projects
Organizational Units
Journal Issue
Keywords
Physics, Astrophysics, Plasma physics, Astrophysics, Black Holes, Cascade, MHD, Plasma, Weibel Instability