The coalescence of degenerate helium cores during red giant collisions—a process we term “erythrohenosis”—introduces a novel class of transient astrophysical sources of high-energy neutrinos. Using stellar models generated with mesa and smoothed-particle hydrodynamics simulations of the final inspiral phase, we develop a semianalytical model to estimate the amount of hydrogen mixed into the cores, the energy release ($\approx 4.28\times {10}^{49}\mathrm{erg}$) that heats the remnant to $T_f\approx 5.3\times {10}^8\mathrm{K}$, the magnetic field amplification ($B\approx 1.77\times {10}^{10}\mathrm{G}$), and the resulting neutrino flux. The predicted TeV–PeV neutrino signal may contribute to the diffuse IceCube neutrino flux; we estimate that the horizon at which a single neutrino event is expected on average at $\gtrsim 100\mathrm{TeV}$ is $\approx 55\mathrm{kpc}$ for individual merger events. Furthermore, we discuss the probability of a magnetized helium flash and assess the subsequent activation of the CNO cycle in the remnant core due to hydrogen mixing. In particular, neutrinos from the decay of ${}^{18}\mathrm{F}$ offer a direct observational test of the detonation, (as sources within $\sim 4.4\mathrm{pc}$ would produce a neutrino flux exceeding the solar CNO neutrino background). The simultaneous emission of high-energy hadronic neutrinos, gravitational waves, and—if the optical depth permits (${\tau }_{\mathrm{T}}\sim {10}^{14}$ in the core of the remnant)—an electromagnetic signal would constitute a unique multimessenger signature of red giant core collisions, positioning erythrohenosis events as exotic yet potentially observable phenomena in dense stellar systems.

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• Gravitational wave sources
• H & He burning
• Particle astrophysics
• Transient & explosive astronomical phenomena
• Cosmic ray & astroparticle detectors