Fallback Accretion Rates and Late Remnant Growth After Core Collapse

Material that fails to reach escape velocity returns to the remnant on a predictable schedule. The classic t to the minus five thirds fallback law governs late accretion in many transients. This paper integrates the law, quantifies late remnant growth, and asks when fallback alone can push a neutron star remnant over its mass ceiling. Using the calculation described in the Methods, the headline results are: Mdot_10s_Msun_s = 0.02, Mdot_1000s_Msun_s = 9e-06, integrated_fallback_Msun_10_to_inf = 0.3. With the adopted normalisation the total late fallback is a few tenths of a solar mass, enough to matter for remnants born close to the ceiling but not enough to convert a typical remnant on its own. Steeper indices reduce the total substantially, so claims of fallback-driven black hole formation must state both the normalisation epoch and the index, not the index alone. This study is simulated and computed from stated assumptions; it is not a measurement. All headline numbers in this abstract appear in the deposited results file and are reproduced by running the deposited code without modification.