The influence of gravitational acceleration on the supernova-driven Parker instability

Abstract

Within a framework of 2D magnetohydrodynamic (MHD) simulations, we explore the dynamical regimes initiated by a supernova explosion in a magnetized stratified interstellar medium (ISM). We concentrate on the formation of large‐scale magnetic structures and outflows connected with the Parker instability. For the sake of simplicity we only show models with a fixed explosion energy corresponding to a single supernova (SN) occurring in host galaxies with different fixed values of the gravitational acceleration g and different ratios of specific heats. We show that in general, depending on these two parameters, three different regimes are possible: a slowly growing Parker instability on time‐scales much longer than the galactic rotation period for small g; the Parker instability growing at roughly the rotation period, which for ratios of specific heats larger than one is accompanied by an outflow resulting from the explosion for intermediate g; and a rapidly growing instability and a strong blow‐out flow for large g. By means of numerical simulations and analytical estimates we show that the explosion energy and gravitational acceleration which separate the three regimes scale as Eg2∼constant in the 2D case. We expect that in the 3D case this scaling law is Eg3∼constant. Our simulations demonstrate furthermore that a single SN explosion can lead to the growth of multiple Parker loops in the disc and large‐scale magnetic field loops in the halo, extending over 2–3 kpc horizontally and up to 3 kpc vertically above the mid‐plane of the disc.

Magnetic Reconnection Triggered by the Parker Instability in the Galaxy: Two‐dimensional Numerical Magnetohydrodynamic Simulations and Application to the Origin of X‐Ray Gas in the Galactic Halo

“…Parker instability is initiated by a small perturbation, a supernova explosion (Kamaya et al 1997;Steinacker & Shchekinov 2001), collision of the highvelocity clouds (HVCs; Santillán et al 2000), and cosmic rays etc. The X-ray gas can be generated, if the magnetic reconnection is triggered by Parker instability or the collision of HVCs (Kerp et al 1994(Kerp et al , 1996.…”

“…The linear analysis of Parker instability were made by many researchers (Shu 1974;Horiuchi et al 1988;Hanawa et al 1992;Foglizzo & Taggar 1994;Chou et al 1997;Kamaya et al 1997). The 2D MHD simulations were performed for solar flares (Kaisig et al 1990;Shibata et al 1992;Yokoyama & Shibata 1996), and the interstellar medium (Basu et al 1997;Matsumoto et al 1998;Santillán et al 2000;Steinacker & Shchekinov 2001). The three-dimensional (3D) simulations of Parker instability of horizontal magnetic field in solar atmosphere and Galaxy (Matsumoto et al 1993;Kim, Ryu, & Jones 2001;Hanasz, Otmianowska-Mazur, & Lesch 2002), and the twisted flux tube in the solar atmosphere (Matsumoto et al 1998;Abbett, Fisher, & Fan 2000;Fan 2001;Magara 2001), the Galaxy (Hanasz & Lesch 2000;France et al 2002), and accretion disks (Ziegler 2001) are also performed.…”