Georgios Moschidis (UC Berkeley)
Title: The instability of Anti-de Sitter spacetime: Recent progress
Abstract: According to the AdS instability conjecture, there exist arbitrarily small perturbations to the initial data of AdS spacetime which, under evolution by the vacuum Einstein equations with reflecting boundary conditions on conformal infinity, lead to the formation of black holes after sufficiently long time. To this day, the question about the vacuum equations remains open (and poorly understood). However, during the last decade, a large number of numerical and heuristic works have been dedicated to addressing the conjecture in the presence of matter fields allowing spherically symmetric dynamics. In this talk, I will present a rigorous proof of the AdS instability conjecture in the setting of the spherically symmetric Einstein--scalar field system. The proof will be based on the non-linear interactions of special configurations of matter beams. The possible extension of the main ideas to the vacuum case will also be discussed.
Jason Dexter (University of Colorado at Boulder)
Title: Accretion Physics from Polarized Black Hole Images
Abstract: Magnetic fields are thought to drive accretion onto black holes and to extract their rotational energy to power relativistic jets. Resolved horizon scale observations with GRAVITY and the Event Horizon Telescope offer a new opportunity to study magnetic fields at the scale where the energy is released. I will discuss the prospects of making such measurements using maps of polarized synchrotron radiation in the Galactic center black hole, Sgr A*, and in M87. Polarization maps trace the magnetic field direction, which in an accretion flow directly relates to its strength. The degree of order of the polarization map further provides information about the temperature and density of radiating electrons, and measuring it constrains the physics of particle heating in collisionless plasmas.