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 the magnetic reconnection triggered by a supernova (or a pointexplosion) in interstellar medium, by performing two-dimensional resistivemagnetohydrodynamic (MHD) numerical simulations with high spatial resolution.We found that the magnetic reconnection starts long after a supernova shock(fast-mode MHD shock) passes a current sheet. The current sheet evolves asfollows: (i) Tearing-mode instability is excited by the supernova shock, andthe current sheet becomes thin in its nonlinear stage. (ii) The current-sheetthinning is saturated when the current-sheet thickness becomes comparable tothat of Sweet-Parker current sheet. After that, Sweet-Parker type reconnectionstarts, and the current-sheet length increases. (iii) ``Secondary tearing-modeinstability'' occurs in the thin Sweet-Parker current sheet. (iv) As a result,further current-sheet thinning occurs and anomalous resistivity sets in,because gas density decreases in the current sheet. Petschek type reconnectionstarts and heats interstellar gas. Magnetic energy is released quickly whilemagnetic islands are moving in the current sheet during Petschek typereconnection. The released magnetic energy is determined by the interstellarmagnetic field strength, not energy of initial explosion nor distance toexplosion. We suggest that magnetic reconnection is a possible mechanism togenerate X-ray gas in Galaxy.