Princeton University Astroplasmas Seminar

Abstract 1: Observations show evidence for the existence of relativistic shock waves in various extreme astrophysical environments, such as gamma-ray bursts and the outflows of binary neutron star mergers. Detailed theoretical models for shock wave hydrodynamics and the radiation that accompanies shock passage are crucial for a correct interpretation of observations, which can help uncover the properties of the systems. In this talk I will discuss our hydrodynamic solution for the interiors of an ultra-relativistic blast wave (Faran & Sari 2021). We obtain a self-similar solution that follows Blandford & McKee (1976) close to the shock wave, at ultra-relativistic velocities, but also describes the flow in the interiors of the blast wave, where the flow reaches mildly-relativistic to Newtonian velocities. I will then discuss our ongoing work on the breakout of a relativistic shock wave from a stellar edge, and highlight applications of this work to low luminosity gamma ray bursts and to the gamma-ray flare that followed GW170817.

Abstract: 2A supermassive binary black hole (SMBBH) might form after two galaxies merge. If the binary reaches subparsec separations, gravitational waves (GW) can efficiently extract energy from the system and the black holes might eventually merge. Contrary to most stellar-mass black holes, SMBBHs might also be powerful sources of electromagnetic radiation accreting the gas of the galaxy. In order to distinguish the electromagnetic signatures of these systems from normal AGNs, we need to analyze the complex non-linear dynamics that occur between the gas and the dynamical spacetime. In this talk, I will present our latest results on GRMHD simulations of accretion disks around spinning SMBBHs. We model the spacetime of a spinning BBH in the inspiral regime using a semi-analytical approximation that we use as a background to evolve the plasma GRMHD equations. We analyze the accretion mechanisms, variability, and electromagnetic luminosities of the circumbinary disk and mini-disks that form around each black hole, focusing on the role of the spin. Finally, we use ray-tracing calculations to obtain light-curves, images, and spectra based on the simulation data.