Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session FA: Nuclei Near Neutron Star Surfaces |
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Chair: Zach Meisel, Ohio Univeristy |
Friday, October 30, 2020 2:00PM - 2:36PM |
FA.00001: Production and Impact of Urca Nuclides Invited Speaker: Wei Jia Ong Observations of Quasi-persistent X-ray transients yield valuable constraints for neutron star physics and structure. The nuclear reactions which occur during the outburst phase determine the composition of the neutron star crust. During the cooling phase, observations probe the thermal structure of the curst. Nuclear reactions such as electron capture and beta decay cycling (Urca cycling) can cool the neutron star, impacting such observations, and may also affect the behavior of X-ray bursts. A thorough understanding of these reactions is therefore necessary for correct interpretation of X-ray observations of X-ray bursts, superbursts, and crustal cooling. The yet- unknown contribution of Urca cooling to the overall cooling of the neutron star depends both on the abundance of potential coolers (the ash composition) as well as the ground state to ground state transition strengths between the Urca pairs. This work will detail a new dedicated experimental program of measurements of ground state beta-decay strengths in potential crust Urca coolers at the National Superconducting Cyclotron Laboratory (NSCL), present first results, and discuss the impact on neutron star cooling. [Preview Abstract] |
Friday, October 30, 2020 2:36PM - 3:12PM |
FA.00002: Bayesian inference of neutron star crust properties from neutron skin and neutron matter constraints Invited Speaker: William Newton We present the first consistent and direct inference of the thickness, mass and composition of the crust and the nuclear pasta layers therein from neutron skin measurements and neutron matter simulations. Using an extended Skyrme model which allows independent variation of the first three symmetry energy coefficients $J$, $L$ and $K_{\rm sym}$ at saturation density, we generate several hundred Skyrme models and calculate the neutron skins of $^{48}Ca$ $^{208}Pb$ and a number of Tin isotopes. We perform MCMC sampling from these results to infer the posterior distributions of the symmetry energy parameters using a number of different priors including ones derived from the results of chiral effective field theory calculations of pure neutron matter. We then sample Skyrme models from the posterior distribution and, within a compressible liquid drop model of the crust fit to the results of 3D Hartree-Fock calculations of the crust, we calculate the posterior distributions of crust and pasta properties. [Preview Abstract] |
Friday, October 30, 2020 3:12PM - 3:48PM |
FA.00003: Deep Crustal Heating and Neutron Star Cooling Observation Invited Speaker: Farrukh Fattoyev In this talk, I will present our recent work on a new mechanism for deep crustal heating in accreting neutron stars. During active accretion, charged pions ($\pi^+$) are produced in nuclear collisions on the neutron star surface. Upon decay, they provide a flux of neutrinos into the neutron star crust. We find that for massive and/or compact neutron stars, neutrinos deposit $\approx 1\textrm{--} 2 \, \mathrm{MeV}$ of heat per accreted nucleon into the inner crust. The strength of neutrino heating is comparable to the previously known sources of deep crustal heating, such as from pycnonuclear fusion reactions, and is relevant for studies of cooling neutron stars. We model the thermal evolution of a transient neutron star in a low-mass X-ray binary, and in the particular case of the neutron star MXB~1659-29, we show that additional deep crustal heating requires a higher thermal conductivity for the neutron star inner crust. A better knowledge of pion production cross sections near the threshold would improve the accuracy of our predictions. [Preview Abstract] |
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