Theoretical Astrophysics

Accretion Disks are flattened, differentially rotating gaseous structures that can be found surrounding young stars, white dwarfs, neutron stars, and black holes. Understanding the physical processes that determine the rate at which matter accretes and energy is radiated in these disks is vital for unraveling the formation, evolution, and fate of almost every type of object in the Universe. We work on several fundamental problems related to the the physical structure and observational properties of these disks. This undertaking entails theoretical and numerical efforts for understanding and modeling the interplay between the generation of magnetized turbulence, the global structure of the accretion disc, and the high-energy radiative processes taking place in the disc and its corona.

Chondrules are spherical grains of silicate material with diameters ~ 1 mm and constitute a ubiquitous class of materials found in primitive meteorites. Their spherical shape and internal textures suggest that they were produced by the rapid melting and slow cooling of silicate dust. Understanding the formation of chondrules has been a long standing problem in cosmo-chemistry with profound implications for the formation and early evolution of the solar system and extra-solar planetary systems. We are currently working on understanding physically viable mechanisms behind the inferred rapid local heating. This requires elucidating, and simulating, the nonlinear dynamics of a mixture of gas and dust, including the ionization, chemistry, and radiative transfer properties.

Jets of a wide range of sizes, from the kiloparsec scale of active galactic nuclei, to the stellar scale of microquasars and forming young stars, are often associated with accretion disks. Such jets of plasma underlie many of the most energetic events in the Universe, such as radio quasars, supernova remnants, and gamma ray bursts. Understanding the physical processes driving the launching, exciting the variability, and maintaining the collimation of jets is a major problem in modern astrophysics. Jets excite powerful shocks, releasing electromagnetic radiation, and accelerating particles to cosmic ray energy levels. Since these energies, temperatures, and densities cannot be reached in the lab, we use simulations to study jet launching, propagation, and shock formation.