Affiliation: INAF-IASF, Milano, Italy

Title: An X-ray view of isolated neutron stars

Abstract: The X-ray spectra of isolated neutron stars (INS) typically include a thermal component, that comes from the cooling surface, and a non-thermal component, produced by highly-relativistic particles accelerated in the stellar magnetosphere. Hot spots from returning currents can also be detected. Middle-aged pulsars exhibit a mixture of these components, but other flavours of INS, that show a large variety of physical parameters (such as spin period, magnetic field and age) emit only thermal X-rays. These are usually detected either by large serendipitous datasets from pointed X-ray observations or from searches in the data of all-sky surveys. The connection between these thermally-emitting INS, the magnetars, and the ordinary pulsars, is one of the current challenges in the study of neutron stars.

Affiliation: Physics Department University of Zagreb, Croatia

Title: Tracing the Symmetry Energy from Collective Dipole Excitations to Rotating Neutron Stars

Abstract: Neutron stars contain the densest observable matter in the Universe, and finite nuclei offer a complementary window on its properties. Both are linked through the nuclear equation of state, in which the density dependence of the symmetry energy remains one of the main sources of uncertainty. In this talk, I will trace the symmetry energy from finite nuclei to neutron stars within the framework of relativistic energy density functionals, focusing on the electric dipole polarizability, a precisely measured property of the collective dipole response. The available measurements constrain the symmetry energy and its slope at saturation density, and through them the bulk properties of neutron stars. A universal relation further connects the dipole polarizability, stellar compactness, and the symmetry-energy slope. The analysis will then be extended to rapidly rotating neutron stars, where the nuclear constraints substantially reduce the uncertainty in the transition between accretion disks that reach the stellar surface and those truncated by orbital instability. Together, these results demonstrate how collective dipole excitations in finite nuclei inform both the structure of neutron stars and the orbital motion in their surrounding spacetime.