Revisiting neutrino-driven magnetogenesis during stellar core collapse

TL;DR

Revisits the viability of neutrino ponderomotive magnetogenesis during stellar core collapse. The authors formulate the magnetic-field evolution under neutrino-coupled MHD in axisymmetry and map collapse dynamics and neutrino fluxes to derive a growth rate for the vertical field $dB_z/dt$. They find that the weak interaction strength, via the Fermi constant, suppresses the effect of neutrino fluxes by many orders of magnitude, yielding pulsar-scale fields unattainable by this mechanism. Consequently, neutrino-driven magnetogenesis appears unlikely to seed global magnetization, though local turbulence or other channels could still influence explosion dynamics.

Abstract

The literature has not converged onto a precise depiction of the magnetogenesis process for pulsars, and it is profitable to preliminarily but exhaustively assess the viability of the plethora of alternative proposals, before substantial efforts are invested into simulating them in detail. In this note, we tackle one of them, taking notice of an earlier work that suggests neutrino ponderomotive force could spawn a magnetic field not so far off from pulsar strengths. We reexamine this mechanism with more modern technology, accounting for actual core collapse dynamics, and show that this mechanism is likely less powerful than originally envisioned.

Figures (8)

• Figure 1: The analytical $\rho_{\rm nuc}$ as a function of the temporal variable $\psi$ (Eq. \ref{['eq:AnaDen']}). The blue, orange and green curves correspond to the center of the core, half way to surface (i.e., at $R/2$), and $99\%$ to surface. The horizontal dashed line marks out $\log_{10}\rho_{\rm nuc} = 11$.
• Figure 2: The numerical $\rho_{\rm nuc}$ as seen in the simulation of 1977ApJ...218..815A, as a function of mass shell index, a fluid frame radius measure. The data (crosses) are taken from their Tb. 1. We also display, as the red curve, a fit to the numerical data. Only the density region adequate for neutrino trapping is fitted.
• Figure 3: The numerical $\hat{G}_{\hat{\xi}}$ as seen in the simulation of 1977ApJ...218..815A, where the original numerical data (from their Fig. 11) is presented as dashed lines, and the quadratic fitting curves are smooth, sharing the same color. Each curve corresponds to a mass shell, with the ones topping out at lower $\hat{G}_{\hat{\xi}}$ values being further out from the center.
• Figure 4: The numerical $\hat{\mathbb{L}}_{\hat{\xi}}$ as seen in the simulation of 1977ApJ...218..815A, where the original numerical data (from their Fig. 9) is presented as dashed lines, and the cubic fitting curves are smooth, sharing the same color. Each curve corresponds to a different neutrino energy $\hat{\xi}$, with the higher energy ones generally residing more to the left, closer to the center of the collapsing core. The black dotted curves are extrapolated ones for energies higher than those tabulated by the numerical study. Only neutrino trapping regions (up to mass shell index $14$) are displayed.
• Figure 5: The $\hat{\xi}$ dependence of the curves in Fig. \ref{['fig:LPlot']}. The points ranging from the lowest to the highest energies correspond to the purple, brown, turquoise, and yellow curves, respectively. The blue markers (left axis) show the $\log_{10}\hat{\mathbb{L}}_{\hat{\xi}}$ value achieved at the peaks of these curves in Fig. \ref{['fig:LPlot']}, while the magenta markers (right axis) display the mass shell index of the peaks.