Session B4: Invited Session: Neutron Star Radii

Measurement of Neutron Star Radii with X-ray Binaries and Recycled Pulsars

Detailed modeling of the observed surface X-ray radiation from neutron stars can in principle reveal their interior structure, thereby constraining the state of matter at the most extreme densities. This talk will provide a summary of on-going observational efforts with the \textit{Chandra X-ray Observatory} and \textit{XMM-Newton} towards this end, with a focus on two particular varieties of neutron stars -- thermally-emitting quiescent low-mass X-ray binaries and ``recycled'' millisecond pulsars. An overview of future prospects for measuring the elusive neutron star equation of state using forthcoming X-ray missions such as the Neutron Star Interior Composition ExploreR (NICER) and Athena+ will also be presented.   

Determining the equation of state via microscopic simulations

I will provide an overview of the status of modern nuclear theory, especially in connection with the determination of the equation of state of nucleonic matter. I will also discuss the relevance of microscopic simulations to the study of strongly interacting nucleons. Starting with some general points on the underlying theory of Quantum Chromodynamics (QCD), I will then go over the efforts toward connecting QCD with many-nucleon studies (via chiral Effective Field Theory [EFT]). I will also introduce a recent local reformulation of chiral EFT, which makes it possible to use such modern potentials within the framework of Quantum Monte Carlo (an essentially exact type of microscopic simulation method).   

Extracting the neutron star equation of state from gravitational wave data

For most of a binary neutron-star inspiral, orbiting point particles in a post-Newtonian framework are a good model for gravitational wave emission, and ground-based detectors can detect signals using these models. However, additional physics near merger is not captured in the detection templates: as the stars coalesce, the gravitational waveforms depend additionally on the properties of dense matter in the core of the stars. The equation of state of dense matter that determines properties such as the neutron-star radius also characterizes the gravitational waveforms emitted during binary neutron-star mergers. Understanding the effects of the equation of state on gravitational waveforms requires information from both analytic models in the inspiral and numerical simulations of the merger. Our current best estimates suggest that these effects will allow Advanced LIGO to constrain the neutron-star equation of state. I will review current models for waveform effects, estimates of measurability, and the implications for equation-of-state constraint in the next decade.