Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session E15: Nuclear Astrophysics I |
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Sponsoring Units: DNP Chair: J. Piekarewicz, Florida State University Room: Hyatt Regency Jacksonville Riverfront City Terrace 11 |
Saturday, April 14, 2007 3:30PM - 3:42PM |
E15.00001: Hot Dilute Neutron Matter and Neutrino Interactions Gautam Rupak The equation of state for hot dilute neutron matter is model-independently calculated to the third order in a virial expansion, at densities and temperatures that are relevant for neutrino-neutron interactions in protoneutron stars. A general formalism for neutron matter with spin polarization is derived using a low-energy effective field theory. The long-wavelength neutrino response is calculated from the virial expansion, and can serve as a benchmark for model calculations that are in current use. The results are also of interest in atomic systems near the Feshbach resonance where universal behavior is expected. [Preview Abstract] |
Saturday, April 14, 2007 3:42PM - 3:54PM |
E15.00002: Heavy Element Synthesis in the Outflow from Black Hole Accretion Disks Rebecca Surman, Sean Kane, Crystal Smith The $r$ process, the rapid neutron capture nucleosynthesis process responsible for half of the elements heavier than iron, is thought to occur in core-collapse supernovae, though the exact site and mechanism is still uncertain. Here we examine an alternate site - the outflows from a very rapidly accreting disk around a stellar mass black hole. We begin with analytic models of black hole accretion disks and use a parameterized outflow to follow the ejected material. We show that neutron capture nucleosynthesis is possible in a wide range of trajectories from very rapidly accreting disks, and that in all cases the neutrino flux emitted from the disk strongly influences the resulting nucleosynthesis. [Preview Abstract] |
Saturday, April 14, 2007 3:54PM - 4:06PM |
E15.00003: Equation of State for Cold Neutron Star Crust Helber Dussan The crust of neutron star has an extension of about 1 km and represents only 1{\%} of the total mass of the star. However, the physical properties (radiation flux, thermal conduction, etc) depend on the dynamics of the crust. We applied relativistic mean field theory to find the equation of state (energy and pressure as functions of the density) for all densities along the crust. [Preview Abstract] |
Saturday, April 14, 2007 4:06PM - 4:18PM |
E15.00004: Spin Response of the Nuclear Pasta Jutri Taruna, Jorge Piekarewicz Neutron-rich matter at subnuclear densities, such as the one present in the crust of a neutron star, displays fascinating complex structures known as pasta phases. Results for the two-body - spin-isospin dependent - correlation function in the nuclear pasta are presented. These results are obtained via semi-classical Monte-Carlo simulations with a Hamiltonian that incorporates a ``semi-classical'' short-range spin-dependent term that is added to simulate Pauli correlations. [Preview Abstract] |
Saturday, April 14, 2007 4:18PM - 4:30PM |
E15.00005: Quantum Monte Carlo and Neutron Star Matter Superfluidity Alex Gezerlis, Joe Carlson, Vijay Pandharipande The equation of state and pairing gap of neutron matter at low densities are important to the structure and cooling of neutron stars, and potentially to the surface properties of neutron-rich nuclei. We find that this system can be well described to significant densities using only the S=L=0 component of a realistic nucleon-nucleon interaction. Diffusion Monte Carlo results are reported for the equation of state and the pairing gap, and compared with BCS calculations and recent Auxiliary Field Diffusion Monte Carlo calculations for neutron matter. [Preview Abstract] |
Saturday, April 14, 2007 4:30PM - 4:42PM |
E15.00006: Relativistically Induced Supernovae M. Dolan, D. Dearborn, G. Mathews, J. Wilson It has been proposed that the relativistic interaction between a black hole and a white dwarf could result in a new form of Type Ia supernovae. The objective of the research reported in this talk has been to determine if under similar conditions a hot red-giant core could be induced to ignite carbon and lead to a supernova explosion. Using a 1-D hydrostatic stellar evolution code, a red giant was evolved from a protostar, and then placed in the gravitational field of a supermassive black hole. During the evolution, helium shell flashes emerged as a serious nuisance causing the numerical calculations to be cumbersome, and at times impossible. However, as the red giant approached, ignition conditions appeared to have robustly occurred. This ignition is a result of the relativistic compression due to the enhanced self gravity as induced by the gravitational field of the black hole and would not have occurred outside this field. The 1-D relativistically compressed model was then mapped into a 3-D hydrodynamic code called Djehuty, capable of simulating whole stars including the appropriate thermonuclear reactions. The Djehuty simulation has shown that ignition had occurred in multiple locations simultaneously. Continuing Djehuty simulations will demonstrate how the ignition propagates through the star leading to a supernova. Prelimminary results indicate that the explosion is forming as an atypical Type II supernova. [Preview Abstract] |
Saturday, April 14, 2007 4:42PM - 4:54PM |
E15.00007: Weak Neutrino Magnetism and the r-Process in the Neutrino-Heated Supernova Bubble Grant Mathews, James Wilson, Kaori Otsuki The neutrino-energized high-entropy bubble above the proto neutron star in a core- collapse supernova remains as one of the most promising sites for r-process nucleosynthesis. However previous studies with this model have encountered the complication that neutrino interactions with material in the expanding bubble limit the production of heavy nuclei by decreasing the ratio of available neutrons to seed nuclei. In this talk we briefly summarize some recent improvements in Livermore supernova model neutrino transport and numerics. Among the important new physics we show that effects of weak magnetism are significant. Above the proto-neutron star, it leads to a high electron anti-neutrino energy at very late times ($t \approx 20$ s post bounce). This means an increased rate of capture on nucleons compared to electron neutrinos. This then shifts the equilibrium electron fraction $Y_e$ to lower values ultimately meaning that more neutrons are available for the $r$-process. Also, very high entropy per baryon ($s/k \sim 600$) appears within the bubble at late times. This makes for efficient neutron production and favorable r-process nucleosynthesis. [Preview Abstract] |
Saturday, April 14, 2007 4:54PM - 5:06PM |
E15.00008: Decrease in Coulomb Barrier Height Due to Nuclear Vibration allowing solar Nuclear Reactions w/o Tunnelling Stewart Brekke The fusing of two protons in the proton-proton is problematic because the interior temperature of the sun would not provide enough thermal energy to overcome the Coulomb barrier electric repulsion between two protons. The artifice of ``tunnelling'' is used to explain the proton-proton reaction. In a previous paper low energy nuclear reactions were explained as possible provided nuclear vibration is conisdered thereby lowering the Coulomb barrier.The vibration adjusted formula is KE needed = $kQ(1)Q(2)/[12A^2\cos^{22}\backslash pift]^2]$. The coulomb barrier is then maximum as infinite, minimum $kQ(1)Q(2)/2(3)^{1/2}A$ with an RMS value of $kQ(1)Q(2)/(6)^{1/2}A$.The great amount of thermal energy on the sun increases the amplitude of vibration thereby lowering the height of the Coulomb barrier dramatically. This increased nuclear vibration makes nuclear reactions such as the proton- proton cycle viable. The need for the artifice of ``tunnelling'' is thereby eliminated. [Preview Abstract] |
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