Time to Black Hole Formation in Failing Cores as a Neutrino Signal Diagnostic

When a proto-neutron star accretes past its hot maximum mass, the neutrino signal ends abruptly. The time from bounce to that cutoff is therefore a direct observable of the accretion history. This paper computes cutoff times across progenitor masses under a constant-rate approximation and compares them with the signal durations future detectors could resolve. Using the calculation described in the Methods, the headline results are: t_BH_fastest_s = 0.31, t_BH_slowest_s = 2, Mmax_hot_Msun = 2.35. Cutoff times range from about two seconds for the most massive progenitor considered to a few tenths of a second at the highest accretion rates. A Galactic failing event would show this cutoff unambiguously in a large detector, turning a non-detection channel, the absence of an explosion, into a measurement of the hot mass ceiling. No current observation provides this test, which is stated plainly as an awaiting opportunity rather than a result. 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.