Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session H6: Nuclear Astrophysics II: Neutron Stars |
Hide Abstracts |
Sponsoring Units: DNP Chair: Charles Horowitz, Indiana University Room: Key 2 |
Sunday, April 12, 2015 8:30AM - 8:42AM |
H6.00001: Pulsar Glitches and the Neutron-Star Matter Equation of State Farrukh J. Fattoyev, Jorge Piekarewicz, Charles J. Horowitz Long time observation of sudden spin jumps in the Vela pulsar suggests that at least 1.6\% of the total moment of inertia must reside in the solid crust. It has been argued that the amount of superfluid entrainment in the crust effectively reduces the angular-momentum reservoir, and in turn suggests that the crustal fraction of the moment of inertia must increase to about 7\%. This indicates that the required angular momentum reservoir may exceed the one available in the crust as predicted by most models of the equation of state. We explore the possibility that uncertainties in the equation of state provide enough flexibility for the construction of models that predict a large crustal moment of inertia. Since the crustal moment of inertia is sensitive to the transition pressure at the crust-core interface, we tune the parameters of the model to maximize the transition pressure, while still providing an excellent description of nuclear observables. In particular, we find that if the neutron-skin thickness of 208Pb falls within the (0.20-0.26) fm range, large enough transition pressures can be generated to explain the large Vela glitches without invoking an additional angular-momentum reservoir beyond that confined to the solid crust. Our results suggest that the crust may be enough. [Preview Abstract] |
Sunday, April 12, 2015 8:42AM - 8:54AM |
H6.00002: Phase conversion dissipation in multi-component compact stars Sophia Han, Mark Alford, Kai Schwenzer We propose a mechanism for the damping of density oscillations in multi-component compact stars. The mechanism is the periodic conversion between different phases, i.e. the movement of the interface between them, induced by pressure oscillations in the star. The damping grows nonlinearly with the amplitude of the oscillation. We study in detail the case of r-modes in a hybrid star with a sharp interface, and we find that the dissipation is vanishingly small at infinitesimal amplitude, but becomes very strong as the amplitude increases. This strong dissipation saturates unstable r-modes in compact stars with a sufficiently large core at amplitudes that are orders of magnitude below those provided by any other known saturation mechanism, and therefore this mechanism is likely to be the dominant one in hybrid stars with a sharp interface. We give a simple analytic prediction for the saturation amplitude, and find that it can be as low as of order $10^{-10}$ for conditions present in observed pulsars. [Preview Abstract] |
Sunday, April 12, 2015 8:54AM - 9:06AM |
H6.00003: Nuclear Mass Predictions for Neutron Stars with a Bayesian Neural Network Raditya Utama, Jorge Piekarewicz Many models have been proposed to estimate the values and uncertainties of nuclear masses that are essential for several nuclear and astrophysical scenarios, such as the composition of the outer crust of a neutron star. Here we apply a Bayesian neural network (BNN) method on the simple liquid drop model and other prominent mass models to make new predictions of nuclear masses. The BNN predictions are computed by fitting the mass difference between the theoretical predictions and the experimental value from the AME2012 compilation. We found that the mass predictions for the crustal region are improved significantly and we are planning to apply BNN techniques in the future to make new predictions for other nuclear observables. [Preview Abstract] |
Sunday, April 12, 2015 9:06AM - 9:18AM |
H6.00004: Nuclear Pasta: Topology and Defects Andre da Silva Schneider, Charles Horowitz, Don Berry, Matt Caplan, Christian Briggs A layer of complex non-uniform phases of matter known as nuclear pasta is expected to exist at the base of the crust of neutron stars. Using large scale molecular dynamics we study the topology of some pasta shapes, the formation of defects and how these may affect properties of neutron star crusts. [Preview Abstract] |
Sunday, April 12, 2015 9:18AM - 9:30AM |
H6.00005: Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars C.J. Horowitz, D.K. Berry, C.M. Briggs, M.E. Caplan, A. Cumming, A.S. Schneider Nuclear pasta, with non-spherical shapes, is expected near the base of the crust in neutron stars. Large scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low conductivity pasta layer by increasing an impurity parameter $Q_{imp}$. Predictions of light curves for the low mass X-ray binary MXB 1659-29, assuming a large $Q_{imp}$, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust). [Preview Abstract] |
Sunday, April 12, 2015 9:30AM - 9:42AM |
H6.00006: Pasta Elasticity: Molecular dynamics simulations of nuclear pasta deformations M.E. Caplan, C.J. Horowitz, D.K. Berry Nuclear pasta is expected in the inner crust of neutron stars at densities near the nuclear saturation density. In this work, the elastic properties of pasta are calculated from large scale molecular dynamics simulations by deforming the simulation volume. Our model uses a semi-classical two-nucleon potential that reproduces nuclear saturation. We report the shear modulus and breaking strain of a variety of pasta phases for different temperatures, densities, and proton fractions. The presence of pasta in neutron stars could have significant effects on crustal oscillations and could be inferred from observations of soft-gamma repeaters. Additionally, these elastic parameters will enable us to improve estimates of the maximum size and lifetime of ``mountains'' on the crust, which could efficiently radiate gravitational waves. [Preview Abstract] |
Sunday, April 12, 2015 9:42AM - 9:54AM |
H6.00007: Properties of Leptons in Hot and Dense Medium Samina Masood We show that the particles propagating in superdense stars like neutron stars and supernova are significantly modified in the presence of their chemical potential and extremely high magnetic field. However, the magnetic dipole moment of electron and the corresponding neutrino flavor is not important in the early universe because of the weak magnetic field and low mass density. We calculate the effective mass, charge, magnetic moment and other properties of electrons inside the astronomical systems, based on the statistical conditions of those systems. We show that the properties of heavier leptons are more significantly modified in highly dense media and their study is more relevant to the astronomical objects. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700