A Study of the Vertical Motion of Supernova Remnant Bubbles in the Interstellar Medium Drawn from the Results of Three‐Dimensional MHD Simulations

Abstract

In order to determine the circumstances under which isolated SNRs are capable of rising into and enriching the thick disk and Galactic halo, simulations of supernova remnants are performed with the FLASH magnetohydrodynamic code. We performed simulations in which the interstellar magnetic field is parallel to or perpendicular to the Galactic plane, as well as a simulation without a magnetic field. The ambient gas density distribution and gravitational potential are based on observations of our Galaxy. We evolve the remnants to ages of roughly 107 yr. For our simulation without a magnetic field, we compare the evolution of the hot bubble's velocity to the velocity evolution calculated from the buoyant and drag accelerations. We found surprisingly small vertical velocities for the hot gas, from which we estimated the drag coefficient to be 10 for the nonmagnetic simulation. Although we found little buoyant motion of the hot gas during the remnant's lifetime, we found rapid vertical motion of the associated cool dense gas near the end of the remnants life. This motion deformed the remnant into a mushroom-cloud structure similar to those found in previous simulations. The simulation in which we have a 4 μG magnetic field parallel to the Galactic midplane shows a dramatically elongated bubble parallel to the magnetic field. The magnetic field pins the supernova remnant, preventing it from rising. In the simulation with the 4 μG magnetic field perpendicular to the midplane, the hot bubble rises more, indicating that having the magnetic field in the same direction as the gravitational force enhances the rise of the bubble.