Theoretical astrophysics has long relied on numerical simulations as a formidable way to improve our understanding of the dynamics of astrophysical systems. Fortunately, the mathematical framework upon which such simulations are based is nowadays developed to high levels of sophistication. The equations governing the dynamics of relativistic astrophysical systems are an intricate set of coupled, time-dependent partial differential equations, comprising the general relativistic hydrodynamics and magnetohydrodynamics equations (GRHD/GRMHD hereafter) and Einstein’s gravitational field equations. The RIT group has developed significant expertise to handle such systems over the course of the years. There are a number of long-term and ambitious projects dedicated to this area within CCRG.
ACCRETION ONTO SUPERMASSIVE BLACK HOLE MERGERS
Our main GRMHD project involve the accretion of magnetized gas onto one or more supermassive black holes, and to explore associated relativistic phenomena such as jets in active galactic nuclei.
Current estimates suggest that somewhere in the universe a few pairs of supermassive black holes merge every year, leaving behind a still more massive single black hole at the centers of the galaxies where this occurs. The energy release is huge, and the consequences for galactic evolution are very deep (strong correlations between galactic structure and central black hole mass indicate tig
ht feedback between black hole and galaxy growth), but no such event has ever been identified because the overwhelming majority
of the energy is given to gravitational waves, which are as yet undetectable. Nonetheless, simple estimates suggest that there should be enough gas close enough to the merging black holes that, particularly as the two approach one another, there should be photon signals of the impending event.
We are interested in performing calculations that can predict key features of the emitted radiation. Because the interaction between surrounding gas and a pair of black holes bound to one another is extremely complex and involves strongly nonlinear physics---nonlinear MHD turbulence, shock waves, dynamical spacetimes---numerical methods are the only way forward. Our principal simulation code is called HARM3d. It is a finite-volume/finite-difference code written in C by members of the group, for solving the magnetohydrodynamics (MHD) equations of motion in curved spacetime---i.e. in the context of Einstein's theory of general relativity.
Projects and Collaborations:
COMPACT BINARIES MERGERS AND GAMMA RAY BURSTS
Combined general relativistic and magneto-hydrodynamics (GRMHD) simulations are also used to model black hole - neutron star and neutron star - neutron star binaries. These astrophysical sources are believed to be the origin of gamma ray bursts (unexplained blasts of intense electromagnetic radiation).
Projects and Collaborations: