Extend discrete GRHD techniques to supersonic and generalized Bondi–Hoyle–Lyttleton accretion

Develop and implement the discrete spacetime general relativistic hydrodynamics formulation and Gravitas numerical framework, which are validated here for radial Bondi accretion, to cover supersonic Hoyle–Lyttleton accretion and the generalized Bondi–Hoyle–Lyttleton accretion flows onto black holes within discrete spacetimes.

Background

The paper derives and implements a formulation of general relativistic hydrodynamics tailored to discrete spacetimes, and validates it through simulations of radial (Bondi-type) accretion onto Schwarzschild and Kerr black holes using the Gravitas framework. The focus is deliberately on the spherically symmetric, radial case.

In the broader accretion literature, Bondi–Hoyle–Lyttleton accretion encompasses cases with non-zero flow velocity and potentially non-radial, supersonic regimes. The authors explicitly leave extending their discrete spacetime techniques from the radial Bondi case to the supersonic Hoyle–Lyttleton and generalized Bondi–Hoyle–Lyttleton cases as an open research problem.