Hungry or not: how stellar-mass black holes grow (or don't) in dark matter mini-haloes at high resolution

We compare the performance of the popular Bondi-Hoyle-Lyttleton accretion scheme with a simple mass-flux scheme applied to stellar-mass black holes (BHs) across six levels of increasing spatial resolution. Simulating the formation of BHs within cosmological mini-haloes at z similar to 20, we investigate scenarios both with and without supernova events, which result in BHs of initial mass 10.8 and 270M(circle dot), respectively. Our explicit focus on the stellar-mass range pushes the maximum resolution down to sub-10(-3)pc regimes, where more complicated gas dynamics are resolved. We observe efficient growth and rotationally supported, similar to 10(-1)pc-scale discs around all 270M(circle dot) BHs independent of resolution and accretion scheme, though clumps, bars, and spiral arm structures impact stability at high resolution. We analyse the effect of these instabilities on the accretion cycle. In contrast, all bar one of the 10.8M circle dot BHs fail to attract a disc and experience modest growth, even when characteristic scales of accretion and dynamical friction are reasonably resolved. While the two accretion schemes somewhat converge in mass growth for the 270M(circle dot) case over 1Myr, the greater degree of gas fragmentation induces more randomness in the evolution of the 10.8M(circle dot) BHs. We conclude that early universe BHs of M-BH similar to 10(1)M(circle dot) struggle to grow even in gas-rich environments without feedback in comparison to seeds of M-BH similar to 10(2)M(circle dot), and the latter exhibit convergent growth histories across accretion schemes below a resolution of dx=1x10(-3)pc.