Impact of electron capture rates for nuclei far from stability on core-collapse supernovae

Abstract

The impact of electron-capture (EC) cross sections on neutron-rich nuclei on the dynamics of corecollapse during infall and early post-bounce is studied performing spherically symmetric simulations in general relativity using a multigroup scheme for neutrino transport and full nuclear distributions in extended nuclear statistical equilibrium models. We thereby vary the prescription for EC rates on individual nuclei, the nuclear interaction for the EoS, the mass model for the nuclear statistical equilibrium distribution and the progenitor model. In agreement with previous works, we show that the individual EC rates are the most important source of uncertainty in the simulations, while the other inputs only marginally influence the results. A recently proposed analytic formula to extrapolate microscopic results on stable nuclei for EC rates to the high densities and temperatures and the neutron rich region, with a functional form motivated by nuclear-structure data and parameters fitted from large scale shell model calculations, is shown to lead to a sizable (16%) reduction of the electron fraction at bounce compared to more primitive prescriptions for the rates, leading to smaller inner core masses and slower shock propagation. We show that the EC process involves ≈ 130 different nuclear species around 86 Kr mainly in the N = 50 shell closure region, and establish a list of the most important nuclei to be studied in order to constrain the global rates.

What can be learned from a proto-neutron star’s mass and radius?

“…To be more precise, the blue dashed-dotted curve corresponds to the profile at 0 s in Fig. 12 of Pons et al (1999), the orange dashed curve to the model s40 of Liebendörfer et al (2004) and Fischer et al (2009) at 400 ms after the bounce, the green dashed curves to profiles obtained using the Co-CoNuT code (Dimmelmeier et al 2005;Pascal et al 2020) for a s15-type progenitor at 100 ms, 200 ms and 300 ms after the bounce, the magenta dotted curves to the profile for the model lsu40 of Peres et al (2013) and the red dashed curve to the model Λ-u40 of Peres et al (2013), both just before the collapse of the star into a black hole.…”

Improved neutrino-nucleon interactions in dense and hot matter for numerical simulations

“…Except during the last few milliseconds before trapping, pre-bounce deleptonization is dominated by electron captures on neutron-rich nuclei and the bounce properties are affected by the uncertainties on the associated rates [64][65][66]. On the contrary, only small differences for the electron fraction at bounce are expected between different prescriptions for charged-current reactions on free nucleons.…”

Finite-temperature electron-capture rates for neutron-rich nuclei around N=50 and effects on core-collapse supernovae simulations

“…Electron-capture (EC) rates play a key role in various astrophysical phenomena, such as the final evolution of intermediate-mass stars [1,2], core-collapse supernovae (CCSN) [3][4][5][6], thermal evolution of the neutronstar crust [7,8], and nucleosynthesis in thermonuclear supernovae [9,10]. For a recent review work the reader may refer to Ref.…”

“…[11]. CCSN are particularly impacted by the rate of electron captures prior and during the collapse phase as it defines the electron fraction (Y e ), which drives the collapse dynamics and sets the diameter of the core at bounce [5,6]. Indeed, at the onset of the collapse, the combination of a high stellar temperature (T ∼10 GK), high density (ρ ∼10 10 g.cm −3 ), and low entropy (s ∼1kB) leads to a nuclear statistical equilibrium [12] in the core.…”

“…The electron-capture reactions on nuclei dominate because the mass fraction of free nucleons is small compared to that of nuclei [13]. Previous studies [5,6] have shown that the nuclei having the largest impact on the evolution of Y e , and therefore on the production of electron neutrinos, are located along the N = 50 shell closure near 78 Ni and along N = 82 near 128 Pd. At ρ 10 −12 g.cm −3 , the electron-neutrino diffusion timescale becomes longer than the dynamical timescale of the collapse, the electron neutrinos become trapped, and a β-equilibrium establishes [12,14].…”