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

We examine magnetic reconnection triggered by a supernova (or a point explo sion) in the interstellar medium by performing two-dimensional resistive ma gnetohydrodynamic (MHD) numerical simulations with high spatial resolution. We find that magnetic reconnection starts long after a supernova shock (fa st-mode MHD shock) passes a current sheet. A current sheet evolves as follo ws : (1) Tearing-mode instability 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 t o that of the Sweet-Parker current sheet. After that, Sweet-Parker reconnec tion 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 set s in, because gas density decreases in the current sheet. Petschek reconnec tion starts and heats the interstellar gas. Magnetic energy is released qui ckly as magnetic islands move in the current sheet during Petschek reconnec tion. The released magnetic energy is determined by the interstellar magnet ic field strength, not the energy of the initial explosion or the distance to the explosion. We suggest that magnetic reconnection is a possible mecha nism to generate X-ray gas in the Galaxy.