Microphysics in computational relativistic astrophysics - 2011

Recent discoveries, including a 2 solar mass pulsar, rapid cooling in the Cas A supernova remnant, and estimates of masses and radii from photospheric radius expansion bursts and thermal emissions from neutron stars, are able to constrain significantly the properties of dense matter. Implications for the pressure-density relation and properties of superfluids in neutron star interiors will be discussed.

We construct the relativistic equation of state (EOS) of dense matter covering a wide range of temperature proton fraction and density for the use of core-collapse supernova simulations. The study is based on the relativistic mean-field (RMF) theory which can provide an excellent description of nuclear matter andfinite nuclei. The Thomas-Fermi approximation is adopted to describe the non-uniform matter which is composed of a lattice of heavy nuclei.We present two types of results. The first one takes into account only the nucleon degree of freedom while the second one considers additional contributions from Lambda hyperons. We tabulate the resulting EOS with an improved design of ranges and grids.

We present new equations of state (EOS) of nuclear matter for a wide range of temperatures densities and proton fractions for use in supernova and neutron star merger simulations. We employ a full relativistic mean field (RMF) calculation for matter at intermediate density and high density and the Virial expansion of a nonideal gas for matter at low density. We tabulate the resulting EOS in the temperature range T = 0 - 80 MeV the density range nB = 10â

Low-density neutron matter is relevant to the study of neutron-rich nuclei and neutron star crusts. Unpolarized neutron matter has been studied extensively over a number of decades, while experimental guidance has recently started to emerge from the field of ultracold atomic gases. We study population-imbalanced neutron matter (possibly relevant to magnetars and to density functionals of nuclei) applying a Quantum Monte Carlo method that has proven successful in the field of cold atoms. We report on the first ab initio simulations of superfluid low-density polarized neutron matter. For systems with small imbalances, we find a linear dependence of the energy on the polarization, the proportionality coefficient changing with the density. We also present results for the momentum and pair distributions of the two fermionic components.

The inner crust of neutron stars has a remarkable property that it is crystalline as well as superfluid. I will describe the low energy theory of systems with this property in general, and describe how to relate the low energy constants of the theory to derivatives of the free energy with respect to lattice shape and chemical potentials. As an application, I will discuss the mixing of lattice and superfluid modes in the neutron star inner crust.

Recent multidimensional supernova simulations seem to support an assumption that the neutrino-driven mechanism might work to blow up massive stars. However the explosion energies obtained in those simulations are usually not enough to account for the canonical explosion energy of 10^51 ergs. In this contribution we'd like to address whether some new physical elements so far ignored in the supernova simulations would or would not have an impact on the neutrino-heating mechanism such as the effects of neutrino self-interactions nuclear burning and the turbulent heatingdue to the magneto-rotational instability. These effects are included in our 2D simulations with the spectral neutrino transport (Suwa et al. (2010)).In addition we will report our 3D results based on the 3D version of the code and discuss their potential impacts on the explosion mechanism. Based on these results we will compute the gravitational radiation and neutrinoemission and then discuss some prospects towards multi-messenger astronomyof supernova explosions.

For approximately half a century, core-collapse supernovae have posed a vexing puzzle for theorists despite being a major ingredient (and uncertainty) in fields ranging from stellar and galaxy evolution to the interstellar medium. Historically, advances in core-collapse theory have been linked to advances in computing power and software. Supernovae are inherently multi-dimensional objects in which neutrino transport, gravity, hydrodynamic instabilities and convection play important roles. Three-dimensional simulations incorporating sufficient physical fidelity require extensive high-performance computing resources and codes efficient enough to use the associated architecture. In this talk, I will highlight recent advances in the field. In particular, I will discuss the dependence of spatial dimension on the viability of the neutrino mechanism and the origin of pulsar kicks.