Common Envelope Hydrodynamic Simulations

2. Common Envelope Hydrodynamic Simulations


A common envelope phase is a short episode in the lifetime of binary stars in which the two stars evolve inside a shared envelope. This is a promising channel for formation of compact object binaries. Inside the common envelope, the embedded secondary object interacts with the fluids flowing past it, giving rise to dynamical friction drag forces that cause an orbital decay of the embedded object. Additionally, the embedded object can be modified by accretion from the flow around it. I work on three-dimensional local hydrodynamic simulations of flows around compact objects modeling the common envelope inspiral phase. I led a study presenting suites of simulations that demonstrated the dependence of coefficients of accretion and drag forces experienced by embedded compact objects on the common envelope flow and binary parameters. The parameters are—binary mass ratio, relative Mach number of the object’s motion through the gas, density gradients, and gas equation of state. Our work pointed to the key role of the accretion and drag coefficients in modulating the rate of transformation of objects during the common envelope phase, and predicted that the natal mass distribution and characteristic spins of black holes are preserved after common envelope phases.

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