Reactive Flows in Compact Objects

This thesis examines aspects of subsonic reactive flows in stars. Highlighted are fluid flows in which the velocity of the fluid is much less than the local sound speed of the fluid, and where the thermodynamic conditions of the fluid are conducive to nuclear reactions. Reactive flows of this nature are capable of generating self-sustained flame fronts, also known as deflagration waves. An introductory chapter on the astrophysics of reacting flows commences this thesis, followed by four chapters which apply this physics to the interiors of compact objects. The bifurcation between accretion-induced collapse of a white dwarf to a neutron star, and the explosion of the white dwarf in a Type 1a supernovae event is the subject of the second chapter. The fate of the accreting white dwarf is critically dependent upon the propagation speed of the laminar flame front that is ignited near or at the center of the star. The physical properties (speed, width, and density recovery time) of subsonic flame fronts are calculated from first principles, and the resulting implications discussed. Chapter three extends the body of literature on the thermal conductivity due to collisions between relativistic degenerate electrons, and provides convenient expressions for evaluation of the electron-electron contribution to the total thermal conductivity. Merging white dwarfs offer another bifurcation point towards accretion-induced collapse and is the subject of chapter four. Here carbon burning is ignited at the surface of the accreting white dwarf, and propagates inwards toward the center of the dwarf. Collapse of the dwarf to a neutron star probably ensues if the flame propagates to the center. One finds that for each value of the gravitational potential, there is a minimum density (hence a minimum mass) below which the flame becomes quenched before it reaches the center of the white dwarf. Closure of this thesis is attained on a possibly exciting, and certainly speculative note. The development and initial testing of an implicit smooth particle hydrocode, which may turn out to be useful for subsonic reactive flows in multiple dimensions, is presented.