Revisiting the Flip-Flop Instability of Hoyle-Lyttleton Accretion

Understand

We revisit the flip-flop instability of two-dimensional planar accretion using high-fidelity numerical simulations.

• By starting from an initially steady-state axisymmetric solution, we are able to follow the growth of this overstability from small amplitudes.
• In the small-amplitude limit, before any transient accretion disk is formed, the oscillation period of the accretion shock is comparable to the Keplerian period at the Hoyle-Lyttleton accretion radius (R_a), independent of the size of the accreting object.
• The growth rate of the overstability increases dramatically with decreasing size of the accretor, but is relatively insensitive to the upstream Mach number of the flow.