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Astron. Astrophys. 350, 230-239 (1999)


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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

1 Department of Physical Sciences, Astronomy Division, University of Oulu, P.O. Box 3000, FIN-90401 Oulu, Finland
2 Department of Mathematics, University of Newcastle, Newcastle upon Tyne NE1 7 RU, UK

Received 25 May 1999 / Accepted 15 July 1999

Abstract

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 [FORMULA] of thermal energy and [FORMULA] of gas in a small volume. We implement a superbubble with the luminosity [FORMULA] 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[FORMULA] for the warm and hot gas, respectively. At the developed state of the simulation there is a magnetic field of 1.3[FORMULA] 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

© European Southern Observatory (ESO) 1999

Online publication: September 24, 1999

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