Colloquium: Dr. Vladimir Zhdankin | Flatiron Institute
In-Person PHYS 401
Location
Physics : 401
Date & Time
February 13, 2023, 11:00 am – 12:00 pm
Description
TITLE: Toward a first-principles theory of astrophysical particle acceleration by turbulence
ABSTRACT: Observations of cosmic rays and broadband radiation spectra imply the prevalence of relativistic particles in high-energy astrophysical systems. Turbulence is a leading candidate process for energizing these particles, but has long been challenging to model due to the complicated, multi-scale nonlinear dynamics of collisionless plasmas. Particle-in-cell (PIC) simulations of relativistic turbulence have recently opened this topic to rigorous, first-principles numerical scrutiny. I will describe recent progress on understanding turbulent plasma energization in parameter regimes relevant for systems such as pulsar wind nebulae, black-hole accretion flows, and relativistic jets. PIC simulations demonstrate efficient turbulent particle acceleration and confirm its diffusive nature, providing the first validation for analytical frameworks dating back to Enrico Fermi in 1949. However, modeling the power-law energy distribution of accelerated particles requires stepping beyond these frameworks, and points to the need for a generalized theory of statistical mechanics. PIC simulations also give new insights into two-temperature electron-ion plasmas and intermittent flares in radiative turbulence, which are essential for modeling emission from accretion flows around black holes such as Sgr A*, recently imaged by the Event Horizon Telescope. The next several years promise to bring fundamental breakthroughs to this frontier of plasma astrophysics.
ABSTRACT: Observations of cosmic rays and broadband radiation spectra imply the prevalence of relativistic particles in high-energy astrophysical systems. Turbulence is a leading candidate process for energizing these particles, but has long been challenging to model due to the complicated, multi-scale nonlinear dynamics of collisionless plasmas. Particle-in-cell (PIC) simulations of relativistic turbulence have recently opened this topic to rigorous, first-principles numerical scrutiny. I will describe recent progress on understanding turbulent plasma energization in parameter regimes relevant for systems such as pulsar wind nebulae, black-hole accretion flows, and relativistic jets. PIC simulations demonstrate efficient turbulent particle acceleration and confirm its diffusive nature, providing the first validation for analytical frameworks dating back to Enrico Fermi in 1949. However, modeling the power-law energy distribution of accelerated particles requires stepping beyond these frameworks, and points to the need for a generalized theory of statistical mechanics. PIC simulations also give new insights into two-temperature electron-ion plasmas and intermittent flares in radiative turbulence, which are essential for modeling emission from accretion flows around black holes such as Sgr A*, recently imaged by the Event Horizon Telescope. The next several years promise to bring fundamental breakthroughs to this frontier of plasma astrophysics.
