Session B5: Invited Session: Relativistic Turbulence and MHD

General Relativistic Magnetohydrodynamic Simulations of Compact Binary Mergers

In several astrophysical scenarios, compact objects, such as neutron stars (NSs) and black holes (BHs), are often surrounded by magnetic fields. Magnetic fields can play an important role in the dynamics of these objects and in the production of powerful electromagnetic emissions. In the case of NS-NS and NS-BH binaries, for example, magnetic fields can be amplified during the merger, via plasma instabilities, and subsequently produce the relativistic jets that may give rise to short gamma-ray bursts (SGRBs). During the merger of supermassive BHs, magnetized accretion disks surrounding the BHs can instead produce strong electromagnetic emissions that may be used to localize these events. In this talk I will review the current status of general relativistic magnetohydrodynamic simulations of compact binary mergers. I will in particular focus on the role that magnetic fields have in the dynamics of the merger of NS-NS, NS-BH, and BH-BH binaries. I will also discuss how a better understanding of how turbulence may affect magnetic field evolution plays an important role in these simulations.   

General Relativistic Radiation Magnetohydrodynamic Simulations of Black Hole Accretion

In this talk, I will review recent progress in adding radiation physics to global, general relativistic magnetohydrodynamic (GRMHD) simulations of black hole accretion, starting from a purely optically thin treatment, then transitioning to purely optically thick, and finally discussing the current prospects for treatments that can capture the full range of optical depths. The optically thin treatment is the easiest to implement, as the radiation simply enters the GRMHD equations as a cooling term, although the physics of the radiative processes themselves can be challenging to treat accurately. The optically thick treatment that I will discuss solves the radiation equations in a form very similar to the GRMHD equations, making its implementation relatively straightforward, although the method has significant limitations, motivating current efforts to advance it further. Throughout the talk I will show examples of how these various versions of radiation MHD have already been applied to the study of black hole accretion in different regimes.