Abstract
Abstract. Recent particle-in-cell (PIC) simulation studies have addressed particle acceleration and magnetic field generation in relativistic astrophysical flows by plasma phase space structures. We discuss the astrophysical environments such as the jets of compact objects, and we give an overview of the global PIC simulations of shocks. These reveal several types of phase space structures, which are relevant for the energy dissipation. These structures are typically coupled in shocks, but we choose to consider them here in an isolated form. Three structures are reviewed. (1) Simulations of interpenetrating or colliding plasma clouds can trigger filamentation instabilities, while simulations of thermally anisotropic plasmas observe the Weibel instability. Both transform a spatially uniform plasma into current filaments. These filament structures cause the growth of the magnetic fields. (2) The development of a modified two-stream instability is discussed. It saturates first by the formation of electron phase space holes. The relativistic electron clouds modulate the ion beam and a secondary, spatially localized electrostatic instability grows, which saturates by forming a relativistic ion phase space hole. It accelerates electrons to ultra-relativistic speeds. (3) A simulation is also revised, in which two clouds of an electron-ion plasma collide at the speed 0.9c. The inequal densities of both clouds and a magnetic field that is oblique to the collision velocity vector result in waves with a mixed electrostatic and electromagnetic polarity. The waves give rise to growing corkscrew distributions in the electrons and ions that establish an equipartition between the electron, the ion and the magnetic energy. The filament-, phase space hole- and corkscrew structures are discussed with respect to electron acceleration and magnetic field generation.
Highlights
Accreting compact objects such as neutron stars and black holes are a source of energetic plasma flows
As the plasma is attracted towards the compact object, it is accelerated to relativistic speeds
Particle-in-cell simulations are being used as computer experiments to better understand the plasma dynamics in energetic astrophysical plasmas
Summary
Accreting compact objects such as neutron stars and black holes are a source of energetic plasma flows. They can, give insight into the magnetic field strengths and the maximum particle energies that can be reached in a kinetic plasma under idealized conditions, because the considered structures play a key role in the dynamics of collisionless shocks These estimates can, in turn, be compared to the observed magnetic field strengths and bulk plasma energies that are thought to be representative for the jets of accreting compact objects. Parametric studies of the elementary phase space structures permit us to assess how the peak magnetic field strength and the possible particle acceleration scales, for example, with the initial beam speed or composition This scaling can, potentially, be compared with observations of the synchrotron emissions of astrophysical jets and it can reveal interesting initial conditions for global shock simulations.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
