Numerical Simulations of Mach Stem Formation via Intersecting Bow Shocks

TL;DR

This study uses 2-D numerical simulations to investigate the formation of Mach stems at intersecting bow shocks in astrophysical jets, aiming to understand their physical and observational implications.

Contribution

First numerical exploration of Mach stem formation at intersecting bow shocks in hypersonic astrophysical flows, validating steady-state theory through simulations.

Findings

Mach stem formation depends on intersection angle and adiabatic index

Simulation results align with steady-state Mach stem theory

Insights into brightness enhancement in stellar jets

Abstract

Hubble Space Telescope observations show bright knots of H$\alpha$ emission within outflowing young stellar jets. Velocity variations in the flow create secondary bow shocks that may intersect and lead to enhanced emission. When the bow shocks intersect at or above a certain critical angle, a planar shock called a Mach stem is formed. These shocks could produce brighter H$\alpha$ emission since the incoming flow to the Mach stem is parallel to the shock normal. In this paper we report first results of a study using 2-D numerical simulations designed to explore Mach stem formation at the intersection of bow shocks formed by hypersonic "bullets" or "clumps". Our 2-D simulations show how the bow shock shapes and intersection angles change as the adiabatic index $\gamma$ changes. We show that the formation or lack of a Mach stem in our simulations is consistent with the steady-state Mach stem formation theory. Our ultimate goal, which is part of an ongoing research effort, is to characterize the physical and observational consequences of bow shock intersections including the formation of Mach stems.