Identifying Thorne-\.Zytkow Objects through Neutrinos

Abstract

Thorne-\.Zytkow Objects (T\.ZOs) have been predicted to form when a neutron star is engulfed by a diffuse, convective giant envelope. Accretion onto a neutron star at a rate that is larger than $10^{-4}\, M_\odot$ yr$^{-1}$ is expected to lead to significant emission of neutrinos of all flavors with energy of $1$-$100$ MeV. Since the neutrino signal is expected to largely vary in time (from milliseconds to thousands of years), we outline detection strategies tailored to the signal duration. We find that neutrino detection from T\.ZOs up to the Small Magellanic Cloud is within the reach of current- and next-generation neutrino observatories, such as Super- and Hyper-Kamiokande, the IceCube Neutrino Observatory, and JUNO. Interestingly, if targeted searches for neutrinos from T\.ZO candidates (e.g.VX Sgr in our Galaxy as well as HV 2112 and HV 11417 in the Small Magellanic Cloud) should lead to positive results, neutrinos could positively identify the nature of such sources and their accretion rate. Furthermore, the diffuse supernova neutrino background may be able to rule out extreme scenarios for the formation and accretion rates of T\.ZOs. Our findings should serve as motivation for establishing dedicated searches for neutrino emission from T\.ZOs. This is especially timely since it is challenging to detect T\.ZOs via electromagnetic radiation unambiguously, and the T\.ZO gravitational wave signal could be probed with next-generation detectors for sources within our Galaxy only.