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Evolution of a superbubble in a turbulent, multi-phased and magnetized ISM
M.J. Korpi 1,
A. Brandenburg 2,
A. Shukurov 2 and
I. Tuominen 1
Received 25 May 1999 / Accepted 15 July 1999
The evolution of a superbubble is simulated using a local three-dimensional, non-ideal MHD model, which includes galactic differential rotation, an external gravitational potential, heating via supernova explosions and radiative cooling of the interstellar medium (ISM). In our model a superbubble is formed due to the clustering of supernova activity, mimicking an OB association. Supernovae are modelled as instantaneous explosions that release of thermal energy and of gas in a small volume. We implement a superbubble with the luminosity into an initial ISM, which is taken from our earlier calculations modelling the warm and hot phases of the ISM. The simulated ISM has a multi-phase structure with hot, dilute and warm, denser gas coexisting in pressure equilibrium; there is also some cold, dense gas in the form of clouds and filaments arising from supernova compression. The multicomponent gas is in a state of developed turbulence, with r.m.s. velocity 10 and 40 for the warm and hot gas, respectively. At the developed state of the simulation there is a magnetic field of 1.3 strength having both uniform and random components.
The evolution of a superbubble is rather different from that indicated by models with quasi-uniform ambient medium. The superbubble loses its spherical symmetry at very early stages of expansion. Its break-through from the disc is strongly facilitated by the nonuniformity of its environment. A superbubble which would be confined in the disc according to criteria obtained for a quasi-uniform ISM can break out to the halo.
Key words: Magnetohydrodynamics (MHD) turbulence ISM: general ISM: structure ISM: supernova remnants
Send offprint requests to: M.J. Korpi
Online publication: September 24, 1999