Collisionless accretion onto black holes: dynamics and flares

Abstract

We study the accretion of collisionless plasma onto a rotating black hole from first principles using axisymmetric general-relativistic particle-in-cell simulations. We carry out a side-by-side comparison of these results to analogous general-relativistic magnetohydrodynamic simulations. Although there are many similarities in the overall flow dynamics, three key differences between the kinetic and fluid simulations are identified. Magnetic reconnection is more efficient, and rapidly accelerates a nonthermal particle population, in our kinetic approach. In addition, the plasma in the kinetic simulations develops significant departures from thermal equilibrium, including pressure anisotropy that excites kinetic-scale instabilities, and a large field-aligned heat flux near the horizon that approaches the free-streaming value. We discuss the implications of our results for modeling event-horizon scale observations of Sgr A* and M87 by GRAVITY and the Event Horizon Telescope.

10 pages, 8 figures, submitted

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• Particle acceleration by magnetic Rayleigh-Taylor instability: mechanism for flares in black-hole accretion flows
• Fitting the light curves of Sagittarius A* with a hot-spot model
• Strongly magnetized accretion with low angular momentum produces a weak jet
• Bulk Motions in the Black Hole Jet Sheath as a Candidate for the Comptonizing Corona
• Survey of Radiative, Two-Temperature Magnetically Arrested Simulations of the Black Hole M87* I: Turbulent Electron Heating
• Adiabatic Index in Fluid Models of Collisionless Black Hole Accretion
• Electromagnetic Energy Extraction from Kerr Black Holes: Ab-Initio Calculations
• Whispering in the dark: Faint X-ray emission from black holes with OB star companions
• Comparison of magnetic diffusion and reconnection in ideal and resistive relativistic magnetohydrodynamics, ideal magnetodynamics, and resistive force-free electrodynamics
• Investigating non-Keplerian motion in flare events with astrometric data
• Scale Statistics of Current Sheets in Relativistic Collisionless Plasma Turbulence
• Discontinuous Galerkin Representation of the Maxwell-Jüttner Distribution
• Bondi-type accretion onto a Kerr black hole in the kinetic regime
• Extreme magnetic fields around black holes
• Auto- and cross-correlations for multiple images of corotating hotspots in accretion disks
• FPIC: a new Particle-In-Cell code for stationary and axisymmetric black-hole spacetimes
• Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign
• Driven Collisionless Reconnection of Force-free Flux Tubes: From Onset to Coalescence