Asymmetric emissions of neutrinos in the cooling of rotating proto-neutron stars

TL;DR

This paper investigates the asymmetry in neutrino emissions from rotating proto-neutron stars, analyzing how rotation affects luminosity, gravitational wave production, and potential flavor conversion signatures.

Contribution

It introduces axisymmetric models of rotating proto-neutron stars with detailed neutrino transport, revealing asymmetries in neutrino luminosity and gravitational wave signals, and identifies signatures of fast flavor conversion.

Findings

Neutrino luminosity varies by about 3% depending on observer position in rotating models.

Low-frequency gravitational waves from neutrino asymmetries could be detected by planned observatories.

Crossings in angular distributions indicate potential fast flavor conversion near the PNS surface.

Abstract

We evaluate global asymmetry in the luminosities of neutrinos emitted from rapidly-rotating proto-neutron stars (PNS's). We build axisymmetric models of PNS's in mechanical equilibrium with rotation by adding prescribed angular momentum distributions by hand to non-rotational PNS models, which are extracted from a one-dimensional (spherically symmetric) PNS cooling calculation at different times: \(t=2, 6, 10, 20, 30\)s after a supernova explosion. We then conduct two-dimensional (spatially axisymmetric) neutrino transport calculations on top of them with the matter profiles (and the spacetime geometry) fixed. We find for the rapidly-rotating models with \(T/|W|\sim 5\times 10^{-2}\) that the neutrino luminosity changes by \(\sim 3 \% \) depending on the observer position. We give detailed analyses of the neutrino-hemispheres as well as the neutrino luminosities that are defined observer-wise. We also calculate the low-frequency (\(\lesssim 1{\rm Hz}\)) gravitational waves produced by the neutrinos radiated asymmetrically. We find that those gravitational waves, if emitted from the Galactic center, can be detected by planned detectors such as B-DECIGO, DECIGO and AILA. Finally, we look for crossings in the energy-integrated angular distributions in momentum space for the electron neutrino sector, a signature of the fast flavor conversion. We find them near the PNS surface in all models.