Aaron Worley

Nuclear Constraints on the Moments of Inertia of Neutron Stars

The properties and structure of neutron stars are determined by the equation of state (EOS) of neutron-rich stellar matter. While the collective flow and particle production in relativistic heavy-ion collisions have tightly constrained the EOS of symmetric nuclear matter up to about 5 times the normal nuclear matter density, more recent experimental data on isospin diffusion and isoscaling in heavy-ion collisions at intermediate energies have constrained considerably the density dependence of the nuclear symmetry energy at subsaturation densities. Although there are still many uncertainties and challenges to pin down completely the EOS of neutron-rich nuclear matter, heavy-ion reaction experiments in terrestrial laboratories have limited the EOS of neutron-rich nuclear matter to a range much narrower than that spanned by the various EOSs currently used in astrophysical studies in the literature. These nuclear physics constraints could thus provide more reliable information about the properties of neutron stars. Within well-established formalisms using the nuclear-constrained EOSs, we study the moments of inertia of neutron stars. We place special emphasis on component A of the extremely relativistic double neutron star system PSR J0737–3039. Its moment of inertia is found to be between 1.30 × 1045 and 1.63 × 1045 g cm2. Moreover, the transition density at the crust-core boundary is shown to lie in the narrow range ρt = 0.091-0.093 fm−3.

Constraining Properties of Rapidly Rotating Neutron Stars Using Data from Heavy-Ion Collisions

Properties, structure, and thermal evolution of neutron stars are determined by the equation of state of stellar matter. Recent data on isospin diffusion and isoscaling in heavy-ion collisions at intermediate energies as well as data on the size of the neutron skin in 208Pb have considerably constrained the density dependence of the nuclear symmetry energy and, in turn, the equation of state of neutron-rich nucleonic matter. These constraints could provide useful information about the global properties of rapidly rotating neutron stars. Models of rapidly rotating neutron stars are constructed by applying several nucleonic equations of state. Particular emphasis is placed on configurations rotating rigidly at 716 and 1122 Hz. The range of allowed hydrostatic equilibrium solutions is determined and tested for stability. The effect of rotation on the internal composition and thermal properties of neutron stars is also examined. At a given rotational frequency, each equation of state yields a range of possible neutron stars configurations restricted by the Keplerian (mass-shedding) limit, corresponding to the maximal circumferential radius, and the limit due to the onset of instabilities with respect to axisymmetric perturbations, corresponding to the minimal equatorial radius of a stable neutron star model. We show that the mass of a neutron star rotating uniformly at 1122 Hz is between 1.7 and 2.1 M☉. Central stellar density and proton fraction decrease with increasing rotational frequency with respect to static models and, depending on the exact stellar mass and angular velocity, can drop below the direct Urca threshold, thus closing the fast cooling channel.

Nuclear limits on gravitational waves from elliptically deformed pulsars

Abstract Gravitational radiation is a fundamental prediction of General Relativity. Elliptically deformed pulsars are among the possible sources emitting gravitational waves (GWs) with a strain-amplitude dependent upon the stars quadrupole moment, rotational frequency, and distance from the detector. We show that the gravitational wave strain amplitude h 0 depends strongly on the equation of state of neutron-rich stellar matter. Applying an equation of state with symmetry energy constrained by recent nuclear laboratory data, we set an upper limit on the strain-amplitude of GWs produced by elliptically deformed pulsars. Depending on details of the EOS, for several millisecond pulsars at distances 0.18 kpc to 0.35 kpc from Earth, the maximal h 0 is found to be in the range of ∼ [ 0.4 – 1.5 ] × 10 −24 . This prediction serves as the first direct nuclear constraint on the gravitational radiation. Its implications are discussed.

Constraining the EOS of Neutron-Rich Nuclear Matter and Properties of Neutron Stars with Heavy-Ion Reactions

Heavy‐ion reactions especially those induced by radioactive beams provide useful information about the density dependence of the nuclear symmetry energy, thus the Equation of State of neutron‐rich nuclear matter, relevant for many astrophysical studies. The latest developments in constraining the symmetry energy at both sub‐ and supra‐saturation densities from analyses of the isopsin diffusion and the π−/π+ ratio in heavy‐ion collisions using the IBUU04 transport model are discussed. Astrophysical ramifications of the partially constrained symmetry energy on properties of neutron star crusts, gravitational waves emitted by deformed pulsars and the w‐mode oscillations of neutron stars are presented briefly.