Speaker
Description
Formed in the aftermath of gravitational core-collapse supernova explosions, neutron stars are the most compact observed stars. Their average density exceeds that found inside atomic nuclei. Neutron stars are also endowed with the highest magnetic fields known, which can reach millions of billion times that of the Earth. According to our current understanding, a neutron star is stratified into distinct layers. The surface is probably covered by a metallic ocean. The solid layers beneath consist of a crystal lattice of pressure-ionized atoms embedded in a highly degenerate relativistic electron gas. With increasing density, nuclei become progressively more neutron rich until neutrons start to drip out of nuclei thus delimiting the boundary between the outer and inner regions of the crust, where neutron-proton clusters are immersed in a neutron liquid. At about half the nuclear saturation density, the crust dissolves into a homogeneous liquid mixture of nucleons and leptons. A mantle of nuclear pasta might also be present at the interface between the crust and the core.
Over the past years, we have developed a series of unified equations of state of dense matter in neutron stars. Based on the nuclear energy-density functional theory, these equations of state provide a thermodynamically consistent treatment of all regions of the star and were calculated using functionals that were precision fitted to experimental and theoretical nuclear data. These equations of state were specifically constructed to assess the role of nuclear uncertainties on neutron-star properties. Our latest developments concern the inclusion of neutron pairing in the inner crust, refined calculations of the pressure and chemical potentials, and a more realistic description of nuclear pasta. These equations of state will be compared to constraints inferred from the detection of the gravitational-wave signal GW170817 from a binary neutron-star merger and from observations of the electromagnetic counterparts. Constraints inferred from other observations including NICER will be also discussed.
