Detectable MeV Neutrino Signals from Neutron-Star Common-Envelope Systems

Common-envelope evolution - where a star is engulfed by a companion - is a critical but poorly understood step in, e.g., the formation pathways for gravitational-wave sources. However, it has been extremely challenging to identify observable signatures of such systems. We show that for systems involving a neutron star, the hypothesized super-Eddington accretion onto the neutron star produces MeV-range, months-long neutrino signals within reach of present and planned detectors. While there are substantial uncertainties on the rate of such events (0.01-1/century in the Milky Way) and the neutrino luminosity (which may be less than the accretion power), this signal can only be found if dedicated new analyses are developed. If detected, the neutrino signal would probe super-Eddington accretion, leading to significant new insights into the astrophysics of common-envelope evolution.