Detection horizon for the neutrino burst from the stellar helium flash

Low-mass stars (M2M_) ignite helium under degenerate conditions, eventually causing a nuclear run-away; the helium flash. The alpha-capture process on ¹⁴N produces a large amount of ¹⁸F, whose subsequent decay spawns an intense νₑ burst (with average energy of 0.38 MeV) lasting about a day. We show that, in addition, a strong 1.7 MeV neutrino line is generated by electron capture on ¹⁸F. Detection is hindered by large backgrounds in state-of-the-art neutrino observatories, such as JUNO. In next-generation facilities, such as the Jinping neutrino experiment, the horizon for a detection with a local significance of 3σ would be extended to almost 3 pc. Although helium flashes occur a few times per year in our Galaxy, there are no stellar candidates approaching the tip of the red giant branch within 10 pc. Hence, to date, asteroseismology remains the most promising tool for probing the most energetic thermonuclear event in the life of a low-mass star.