Session Y2: Massive Neutron Stars and Dense Matter

A Two Solar Mass Neutron Star

There are over 200 known radio millisecond pulsars in the Galaxy and its globular cluster system. These incredibly stably and rapidly rotating neutron stars can be ``timed'' over timescales of weeks to decades to provide extremely precise measurements of a variety of interesting physical parameters and/or effects. Improvements in timing precision and a doubling of the number of known millisecond pulsars over the past 5-6 years are allowing us to make significantly better mass measurements of many neutron stars. In this talk I report on recent progress in the field, including a precise measurement of a two Solar mass neutron star, PSR J1614-2230, via relativistic Shapiro delay. This single measurement has many implications for the nature of matter at supra-nuclear densities and on a variety of topics in astrophysics.   

Quark matter and neutron stars

I discuss some of the signatures by which the presence of quark matter in neutron stars might be inferred from observations. I show how the recent observation of a heavy neutron star places strong constraints on the quark matter equation of state, and I survey some of the distinctive transport properties of the color-superconducting phases of quark matter.   

Constraints on neutron star properties from neutron matter calculations

Microscopic calculations based on chiral effective field theory interactions constrain the properties of neutron-rich matter below nuclear densities to a much higher degree than is reflected in current neutron star modeling. Combined with the heaviest $2 \, M_\odot$ neutron star, our results constrain the radius of a typical $1.4 \, M_ \odot$ star to $R = 10.9 - 13.9 \, {\rm km}$. This theoretical range is due, in about equal amounts, to the uncertainty in many-nucleon forces and to the extrapolation to high densities. The radius range is consistent with independent astrophysical results obtained from modeling X-ray burst sources. In addition, we predict the neutron skin thickness of $^{208}$Pb to $0.17 - 0.03 \, {\rm fm}$.