The Frontiers of Event Horizon Scale Accretion

Coordinators: Jason Dexter, Monika Moscibrodzka, Sean Ressler, and Chris White

In order to accurately interpret the new and forthcoming event horizon scale observations of low luminosity active galactic nuclei such as Sagittarius A* (Sgr A*) and the supermassive black hole in M87, an intimate knowledge of the surrounding accretion flow is required. Modeling these systems typically requires fully 3D General Relativistic (GR) Magnetohydrodynamic simulations alongside GR radiative transport calculations. Complicating matters is the fact that the gas at event horizon scales is an essentially collisionless plasma, meaning that a variety of non-ideal effects can be important, for example, nonthermal particle acceleration and two-temperature effects. Moreover, the dynamical range of accretion onto these objects spans many orders of magnitude in distance from the black hole, making it challenging to simulate exactly how gas and magnetic fields are fed from large radii. This is important because changes to the initial conditions in horizon scale simulations (which serve as a proxy for this feeding) can have profound consequences on the resulting flow.

This conference will focus on these issues in the specific contexts of spatially resolved polarization of M87/Sgr A*, the infrared/Xray flares observed in Sgr A*, the physics of particle heating in collisionless plasmas, black hole spin powered jets, and tests of GR. Speakers will be a mix of theorists and observers, with more emphasis on the theorist side.