Possible Early Linear Acceleration of Proto-neutron Stars via Asymmetric Neutrino Emission in Core-collapse Supernovae

Abstract

In this Letter, we present the result of an axisymmetric CCSN simulation conducted with appropriate treatments of neutrino transport and proper motions of proto-neutron star (PNS), in which a remarkable PNS acceleration is observed in association with asymmetric neutrino emissions by the time of 300ms after bounce. We find that these asymmetric neutrino emissions play important roles in the acceleration of PNS in this phase. The correlation between the PNS proper motion and the asymmetric ejecta is similar to that in the neutron star (NS) kick of hydrodynamic origin. Both electron-type neutrinos (ν e ) and their anti-particles (ν e ) have ∼ 10% level of asymmetry between the northern and southern hemispheres, while other heavy-leptonic neutrinos (ν x ) have much smaller asymmetry of ∼ 1%. The emissions ofν e and ν x are higher in the hemisphere of stronger shock expansion whereas the ν e emission is enhanced in the opposite hemisphere: in total the neutrinos carry some linear momentum to the hemisphere of the stronger shock expansion. The asymmetry is attributed to the non-spherical distribution of electron-fraction (Y e ) in the envelope of PNS. Although it is similar to LESA (lepton-emission self-sustained asymmetry), the Y e asymmetry seems to be associated with the PNS motion: the latter triggers lateral circular motions in the envelope of PNS by breaking symmetry of the matter distribution there, which are then sustained by a combination of convection, lateral neutrino diffusion and matter-pressure gradient. Our findings may have an influence on the current theories on the NS kick mechanism although long-term simulations are required to assess their impact on the later evolution.

Fast neutrino-flavor conversion in the preshock region of core-collapse supernovae

“…Realistic models.-Below we vindicate the above argument given for the bulb model by quantitatively analyzing the data obtained in our CCSN simulations with the full Boltzmann neutrino transport. Importantly, the ELN crossings in the pre-shock region are confirmed in many of our models [47,48] and also in those of Garching group, which are publicly available [49]. Tamborra et al [18] reported that there was no ELN crossing in the latter models, which is not true, however.…”

Fast neutrino flavor conversion modes in multidimensional core-collapse supernova models: The role of the asymmetric neutrino distributions

“…The pattern in α is (anti)correlated with a similar pattern in Y e (and T ) that appears very deep inside the PNS and is thought to be caused by the convectional flows therein. This is closely related to LESA [47][48][49][50][51][52][53][54][55] in which strong dipole structure exists in the neutrino distributions which can be preceded by strong higher multipole structures at earlier times. Our study suggests that if the multipole structures (either dipole at later times or higher multipoles at earlier times) are strong enough, they can lead to the existence of zones with significantly large α's and a good chance for the occurrence of ELN crossings.…”

“…However, this story can be changed in multidimensional (multi-D) SN models. Indeed, recent multi-D SN simulations have shown that the neutrino distributions can be highly asymmetric in the presence of lepton-emission self-sustained asymmetry (LESA) [47][48][49][50][51][52][53][54][55]. Such asymmetric neutrino distributions can significantly help increasing the chance of the occurrence of ELN crossings by providing SN zones with smaller difference between nν e and n νe [56].…”

A systematic study of proto-neutron star convection in three-dimensional core-collapse supernova simulations

“…It should be noted that large-scale coherent motions can be triggered by the random breaking of global symmetry in the shocked envelope, not necessarily first in the PNS convective zone, and that asymmetries in the latter might be a consequence of the former. Moreover, such symmetry breaking might be correlated with the PNS kick direction, as suggested by Nagakura et al (2019c). In- Figure 8.…”