Dynamical Friction in a Gas: The Subsonic Case

Understand

We study the force of dynamical friction acting on a gravitating point mass that travels through an extended, isothermal gas.

• This force is well established in the hypersonic limit, but remains less understood in the subsonic regime.
• Using perturbation theory, we analyze the changes in gas velocity and density far from the mass.
• We show analytically that the steady-state friction force is Mdot*V, where Mdot is the mass accretion rate onto an object moving at speed V.