Two‐dimensional Magnetohydrodynamic Numerical Simulations of Magnetic Reconnection Triggered by a Supernova Shock in the Interstellar Medium: Generation of X‐Ray Gas in the Galaxy

Abstract

We examine magnetic reconnection triggered by a supernova (or a point explosion) in the interstellar medium by performing two-dimensional resistive magnetohydrodynamic (MHD) numerical simulations with high spatial resolution. We find that magnetic reconnection starts long after a supernova shock (fast-mode MHD shock) passes a current sheet. A current sheet evolves as follows: (1) Tearing-mode is excited by the supernova shock, and in its nonlinear stage the current sheet becomes thin. (2) The current-sheet thinning is saturated when the current-sheet thickness becomes comparable to that of the Sweet-Parker current sheet. After that, Sweet-Parker reconnection starts, and the current-sheet length increases. (3) Secondary tearing-mode instability occurs in the thin Sweet-Parker current sheet. (4) As a result, further current-sheet thinning occurs and anomalous resistivity sets in, because gas density decreases in the current sheet. Petschek reconnection starts and heats the interstellar gas. Magnetic energy is released quickly as magnetic islands move in the current sheet during Petschek reconnection. The released magnetic energy is determined by the interstellar magnetic field strength, not the energy of the initial explosion or the distance to the explosion. We suggest that magnetic reconnection is a possible mechanism to generate X-ray gas in the Galaxy.