Neutrino emission from the collapse of ∼104 M⊙ Population III supermassive stars

ABSTRACT We calculate the neutrino signal from Population III supermassive star (SMS) collapse using a neutrino transfer code originally developed for core-collapse supernovae and massive star collapse. Using this code, we are able to investigate the SMS mass range thought to undergo neutrino trapping (∼104 M⊙), a mass range which has been neglected by previous works because of the difficulty of neutrino transfer. For models in this mass range, we observe a neutrino sphere with a large radius and low density compared to typical massive star neutrino spheres. We calculate the neutrino light curve emitted from this neutrino sphere. The resulting neutrino luminosity is significantly lower than the results of a previous analytical model. We briefly discuss the possibility of detecting a neutrino burst from an SMS or the neutrino background from many SMSs and conclude that the former is unlikely with current technology, unless the SMS collapse is located as close as 1 Mpc, while the latter is also unlikely even under very generous assumptions. However, the SMS neutrino background is still of interest as it may serve as a source of noise in proposed dark matter direct detection experiments.

The neutrino emission from thermal processes in very massive stars in the local universe

ABSTRACT We present a new overview of the life of very massive stars (VMS) in terms of neutrino emission from thermal processes: pair annihilation, plasmon decay, photoneutrino process, bremsstrahlung, and recombination processes in burning stages of selected VMS models. We use the realistic conditions of temperature, density, electron fraction, and nuclear isotropic composition of the VMS. Results are presented for a set of progenitor stars with mass of 150, 200, and 300 M⊙Z = 0.002 and 500 M⊙Z = 0.006 rotating models which are expected to explode as a pair instability supernova at the end of their life except the 300 M⊙ would end up as a black hole. It is found that for VMS, thermal neutrino emission occurs as early as towards the end of hydrogen burning stage due to the high initial temperature and density of these VMS. We calculate the total neutrino emissivity, Qν and luminosity, Lν using the structure profile of each burning stages of the models and observed the contribution of photoneutrino at early burning stages (H and He) and pair annihilation at the advanced stages. Pair annihilation and photoneutrino processes are the most dominant neutrino energy loss mechanisms throughout the evolutionary track of the VMS. At the O-burning stage, the neutrino luminosity ∼1047−48 erg s−1 depending on their initial mass and metallicity are slightly higher than the neutrino luminosity from massive stars. This could shed light on the possibility of using detection of neutrinos to locate the candidates for pair instability supernova in our local universe.

Analytic solutions for neutrino-light curves of core-collapse supernovae

Neutrino is a guaranteed signal from supernova explosions in the Milky Way and is the most valuable messenger that can provide us with information about the deepest part of supernovae. In particular, neutrinos will provide us with physical quantities, such as the radius and mass of protoneutron stars (PNS), which are the central engine of supernovae. It requires a theoretical model that connects observables such as neutrino luminosity and average energy with physical quantities. Here we show analytic solutions for the neutrino-light curve derived from the neutrino radiation transport equation by employing the diffusion approximation and the analytic density solution of the hydrostatic equation for the PNS. The neutrino luminosity and the average energy as functions of time are explicitly presented, with dependence on PNS mass, radius, the total energy of neutrinos, surface density, and opacity. The analytic solutions provide good representations of the numerical models from a few seconds after the explosion and let our rough estimate of these physical quantities to be made from observational data.

The sensitivity of presupernova neutrinos to stellar evolution models

ABSTRACT We examine the sensitivity of neutrino emission to stellar evolution models for a 15 M⊙ progenitor, paying particular attention to a phase prior to the collapse. We demonstrate that the number luminosities in both electron-type neutrinos (νe) and their antipartners ($\bar{\nu }_\mathrm{ e}$) differ by more than an order of magnitude by changing spatial resolutions and nuclear network sizes on stellar evolution models. We also develop a phenomenological model to capture the essential trend of the diversity, in which neutrino luminosities are expressed as a function of central density, temperature, and electron fraction. In the analysis, we show that the neutrino luminosity can be well characterized by these central quantities. This analysis also reveals that the most influential quantity to the time evolution of νe luminosity is matter density, while it is temperature for $\bar{\nu }_\mathrm{ e}$. These qualitative trends will be useful and applicable to constrain the physical states of progenitors at the final stages of stellar evolution from future neutrino observations, although more detailed systematic studies including various mass progenitors are required to assess the applicability.

Neutrinos and gravitational waves from magnetized neutrino-dominated accretion discs with magnetic coupling

ABSTRACT Gamma-ray bursts (GRBs) might be powered by black hole (BH) hyperaccretion systems via the Blandford–Znajek (BZ) mechanism or neutrino annihilation from neutrino-dominated accretion flows (NDAFs). Magnetic coupling (MC) between the inner disc and BH can transfer angular momentum and energy from the fast-rotating BH to the disc. The neutrino luminosity and neutrino annihilation luminosity are both efficiently enhanced by the MC process. In this paper, we study the structure, luminosity, MeV neutrinos, and gravitational waves (GWs) of magnetized NDAFs (MNDAFs) under the assumption that both the BZ and MC mechanisms are present. The results indict that the BZ mechanism will compete with the neutrino annihilation luminosity to trigger jets under the different partitions of the two magnetic mechanisms. The typical neutrino luminosity and annihilation luminosity of MNDAFs are definitely higher than those of NDAFs. The typical peak energy of neutrino spectra of MNDAFs is higher than that of NDAFs, but similar to those of core-collapse supernovae. Moreover, if the MC process is dominant, then the GWs originating from the anisotropic neutrino emission will be stronger particularly for discs with high accretion rates.

Long-term simulations of multi-dimensional core-collapse supernovae: Implications for neutron star kicks

Core-collapse supernovae (CCSNe) are the final stage of massive stars, marking the birth of neutron stars (NSs). The aspherical mass ejection drives a natal kick of the forming NS. In this work we study the properties of the NS kick based on our long-term hydrodynamics CCSN simulations. We perform two-dimensional (2D) simulations for ten progenitors from a 10.8 to 20$\, M_{\odot }$ star covering a wide range of the progenitor’s compactness parameter, and two three-dimensional (3D) simulations for an 11.2$\, M_{\odot }$ star. Our 2D models present a variety of explosion energies between ∼1.3 × 1050 erg and ∼1.2 × 1051 erg, and NS kick velocities between ∼100 km s−1 and ∼1500 km s−1. For the 2D exploding models, we find that the kick velocities tend to become higher with the progenitor’s compactness. This is because the high progenitor compactness results in high neutrino luminosity from the proto-neutron star (PNS), leading to more energetic explosions. Since high-compactness progenitors produce massive PNSs, we point out that the NS masses and the kick velocities can be correlated, which is moderately supported by observation. Comparing 2D and 3D models of the 11.2$\, M_{\odot }$ star, the diagnostic explosion energy in 3D is, as previously identified, higher than that in 2D, whereas the 3D model results in a smaller asymmetry in the ejecta distribution and a smaller kick velocity than in 2D. Our results confirm the importance of self-consistent CCSN modeling covering a long-term post-bounce evolution in 3D for a quantitative prediction of the NS kicks.

Three-dimensional supernova explosion simulations of 9-, 10-, 11-, 12-, and 13-M⊙ stars

Using the new state-of-the-art core-collapse supernova (CCSN) code fornax, we have simulated the three-dimensional dynamical evolution of the cores of 9-, 10-, 11-, 12-, and 13-M⊙ stars from the onset of collapse. Stars from 8 to 13 M⊙ constitute roughly 50 per cent of all massive stars, so the explosive potential for this mass range is important to the overall theory of CCSNe. We find that the 9-, 10-, 11-, and 12-M⊙ models explode in 3D easily, but that the 13-M⊙ model does not. From these findings, and the fact that slightly more massive progenitors seem to explode, we suggest that there is a gap in explodability near 12 to 14 M⊙ for non-rotating progenitor stars. Factors conducive to explosion are turbulence behind the stalled shock, energy transfer due to neutrino–matter absorption and neutrino–matter scattering, many-body corrections to the neutrino–nucleon scattering rate, and the presence of a sharp silicon–oxygen interface in the progenitor. Our 3D exploding models frequently have a dipolar structure, with the two asymmetrical exploding lobes separated by a pinched waist where matter temporarily continues to accrete. This process maintains the driving neutrino luminosity, while partially shunting matter out of the way of the expanding lobes, thereby modestly facilitating explosion. The morphology of all 3D explosions is characterized by multiple bubble structures with a range of low-order harmonic modes. Though much remains to be done in CCSN theory, these and other results in the literature suggest that, at least for these lower mass progenitors, supernova theory is converging on a credible solution.