Dynamic Evolution Model of Isothermal Voids and Shocks

We explore self-similar hydrodynamic evolution of central voids embedded in an isothermal gas of spherical symmetry under the self-gravity. More specifically, we study voids expanding at constant radial speeds in an isothermal gas and construct all types of possible void solutions without or with shocks in surrounding envelopes. We examine properties of void boundaries and outer envelopes. Voids without shocks are all bounded by overdense shells and either inflows or outflows in the outer envelope may occur. These solutions, referred to as type X void solutions, are further divided into subtypes XI and XII according to their characteristic behaviours across the sonic critical line (SCL). Void solutions with shocks in envelopes are referred to as type Z voids and can have both dense and quasi-smooth edges. Asymptotically, outflows, breezes, inflows, accretions and static outer envelopes may all surround such type Z voids. Both cases of constant and varying temperatures across isothermal shock fronts are analyzed; they are referred to as types ZI and ZII void shock solutions. We apply the ‘phase net matching procedure’ to construct various self-similar void solutions. We also present analysis on void generation mechanisms and describe several astrophysical applications. By including self-gravity, gas pressure and shocks, our isothermal self-similar void (ISSV) model is adaptable to various astrophysical systems such as planetary nebulae, hot bubbles and superbubbles in the interstellar medium as well as supernova remnants. Y.-Q. Lou 1. Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 100084, China; 2. Department of Astronomy and Astrophysics, The University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637 USA; 3. National Astronomical Observatories, Chinese Academy of Sciences, A20, Datun Road, Beijing 100012, China. E-mail: [email protected]; [email protected] X. Zhai Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 100084, China E-mail: [email protected]