Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session K16: Supernovae |
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Sponsoring Units: DAP Chair: Fiona Harrison, Caltech Room: B232-233 |
Sunday, April 15, 2018 3:30PM - 3:42PM |
K16.00001: Magneto-Hydrodynamical Effects On Nuclear Deflagration Fronts In Type Ia Supernovae Boyan Hristov, David Collins, Peter Hoeflich, Charles Weatherford, Tiara Diamond, Alec Fisher We presents the study of the effects of magnetic fields on non-distributed nuclear burning fronts as a possible solution to a fundamental problem for the thermonuclear explosion of a Chandrasekhar mass white dwarf (WD), the currently favored scenario for the majority of Type Ia SNe. All existing 3D hydrodynamical simulations predict strong global mixing of the burning products due to Rayleigh-Taylor instabilities (RTI), which is in contradiction with observations. As a first step and to study the flame physics we use a set of computational MHD models in rectangular flux tubes, resembling a small inner region of a WD. We consider initial magnetic fields up to 1E12 G of various orientation. We find an increasing suppression of RTI starting at about 1E9 G. The front speed tends to decrease with increasing magnitude up to about 1E11 G. For even higher fields new small scale finger-like structures develop, which increase the burning speed by a factor of 3 to 5 above the field-free RTI-dominated model. We suggest that the new instability may provide sufficiently accelerated energy production during the distributed burning regime to go over the Chapman-Jougey limit and trigger a detonation. [Preview Abstract] |
Sunday, April 15, 2018 3:42PM - 3:54PM |
K16.00002: Carbon Detonation Initiation in Highly Turbulent Electron-Degenerate Matter Gabriel Casabona, Robert Fisher Type Ia supernovae play a crucial role as standardizable candles for cosmology, but their stellar progenitors remain mysterious. Underlying this mystery is a crucial physical process: the mechanism of detonation initiation in Type Ia supernovae. Using the FLASH4 code, simulations were run to explore detonation initiation under various initial conditions. Adaptive mesh refinement techniques were utilized in order to refine the limits of successful and unsuccessful detonations. Further research into this topic will clarify the mechanisms giving rise to Type Ia supernovae. [Preview Abstract] |
Sunday, April 15, 2018 3:54PM - 4:06PM |
K16.00003: Impact of electron-captures on nuclei near N = 50 on core-collapse supernovae Rachel Titus, Chris Sullivan, Remco G T Zegers, B Alex Brown, Bingshui Gao Sensitivity studies of the late stages of stellar core collapse with respect to electron-capture rates indicate the importance of a region of nuclei near the N=50 shell closure, just above doubly magic $^{78}$Ni. In the present work, it has been demonstrated that uncertainties in key characteristics of the evolution, such as the lepton fraction, electron fraction, entropy, stellar density, and in-fall velocity are about 50$\%$ due to uncertainties in the electron-capture rates on nuclei in this region, although thousands of nuclei are included in the simulations. The present electron-capture rate estimates used for the nuclei in this region of interest are primarily based on a simple approximation, and it is shown that the estimated rates are likely overestimated by an order of magnitude or more. More accurate microscopic theoretical models are required to obtain Gamow-Teller strength distributions, upon which electron-capture rates are based. The development of these models and the benchmarking of such calculations rely on data from charge-exchange experiments at intermediate energies, and an experimental campaign to study N=50 nuclei with the (t,$^{3}$He) reaction at NSCL will be presented. [Preview Abstract] |
Sunday, April 15, 2018 4:06PM - 4:18PM |
K16.00004: Investigating and reducing the impact of nuclear reaction rate uncertainties on $ce{^{44}Ti}$ production in core-collapse supernovae Shiv Subedi, Zach Meisel Recent observational advances have enabled high resolution mapping of $ce{^{44}Ti}$ in core-collapse supernova (CCSN) remnants. Comparisons between observations and 3D models provide stringent constraints on the CCSN mechanism. However, recent work has identified several uncertain nuclear reaction rates that influence $ce{^{44}Ti}$ production in model calculations. We use MESA (Modules for Experiments in Stellar Astrophysics) as a tool to investigate the previously identified sensitivities of $ce{^{44}Ti}$ production in CCSN to varied reaction rates. MESA is a code for modeling stellar evolution and stellar explosions in one-dimension. We will present our preliminary results of CCSN simulations and sensitivity study and will also discuss our plans to reduce or remove the most significant uncertainties from ($\alpha$, n), ($\alpha$, p), ($\alpha$, $\gamma$), (p, n) and (p, $\gamma$) reaction rates using direct and indirect measurement techniques at the Edwards Accelerator Lab at Ohio University. [Preview Abstract] |
Sunday, April 15, 2018 4:18PM - 4:30PM |
K16.00005: Equation of state effects on core-collapse supernovae Andre da Silva Schneider, Christian Ott, Luke Roberts Using the recently developed SROEOS code we construct many hot dense equations of state (EOSs) of nuclear matter. We use the newly computed EOSs to investigate how different aspects of nuclear matter affect the dynamics and observables of the core-collapse of a massive star and the properties of the resulting proto-neutron star. [Preview Abstract] |
Sunday, April 15, 2018 4:30PM - 4:42PM |
K16.00006: Supernova simulations with variational principle EOS, consistent treatment of nuclear electron capture rates and Boltzmann neutrino transport Hiroki Nagakura, Shun Furusawa, Hajime Togashi, Kohsuke Sumiyoshi, Shoichi Yamada The roles of weak interactions, EOS, neutrino transport in core-collapse supernova are still matters of debate. In this talk, I report our latest results of axisymmetric supernova simulations with multi-energy, multi-angle and multi-species neutrino transport. In these simulations, we update mainly two input physics. (1) Nuclear equation-of-state (EOS) based on a realistic two- and three- body nuclear force in uniform matter employing variational principle method. The obtained EOS also satisfies the current observational constraint. (2) Electron and positron capture rates on heavy and light nuclei based on multi-species nuclear-statistical-equilibrium (NSE) abundances. The NSE nuclear abundance is also consistent with our multi-nuclear species EOS. This improvement is an important step toward getting rid of uncertainties of role of nuclear-weak interactions. I will discuss how these improvements give impacts on the supernova dynamics. [Preview Abstract] |
Sunday, April 15, 2018 4:42PM - 4:54PM |
K16.00007: The effect of turbulence in core-collapse supernovae. Jordi Casanova While it is widely accepted that a neutrino-driven mechanism plays a major role in the onset of the explosion, the nature of it is not fully understood. Recent multi-dimensional studies reveal that the growth of fluid instabilities, combined with the development of convection, will contribute to the morphology of the explosion. We utilize the advanced CHIMERA code, capable to model multi-dimensional simulations of core-collapse supernovae, to study the interplay between turbulence and the dynamics of the explosion. The CHIMERA code is a parallel, multi-physics code, that includes sophisticated nuclear physics and spectral neutrino transport. We have performed a set of wedge simulations (that is, a 90 degree shaped computational domain), for resolutions that vary from a quarter to two degrees. We will present a detailed analysis of the development of turbulence in function of the resolution in two and three dimensions, and will discuss the connection with the progress of the explosion. [Preview Abstract] |
Sunday, April 15, 2018 4:54PM - 5:06PM |
K16.00008: The Gravitational Wave Signal from Core-Collapse Supernovae Viktoriya Giryanskaya (Morozova), David Radice, Adam Burrows, David Vartanyan The ground-based laser interferometers LIGO and Virgo have recently detected the gravitational-wave signal of merging binary systems of black holes and neutron stars. Detection of the gravitational waves from a galactic core-collapse supernova, potentially accompanied by detection of neutrinos and electromagnetic observations in all available bands, could be the next major breakthrough. In this talk, I will present gravitational waves from a set of two-dimensional multi-group neutrino radiation hydrodynamic simulations of core-collapse supernovae. I will demonstrate that starting from $\sim$400 ms after core bounce the dominant gravitational-wave signal comes from the fundamental quadrupole (l = 2) oscillation mode (f-mode) of the proto-neutron star. In addition, I will summarize the dependence of the dominant gravitational-wave frequency on the progenitor mass, equation of state, many-body corrections to the neutrino opacity, and rotation. [Preview Abstract] |
Sunday, April 15, 2018 5:06PM - 5:18PM |
K16.00009: Variability in the winds from magnetized massive stars: effect of unstable magnetosonic modes Koushik Sen, Rodrigo Fernandez The evolution of massive stars is closely related to processes that generate heavy elements in the Universe such as supernova explosions and neutron star mergers. A key component in this evolution is the stellar wind, which displays variability on various spatial and temporal scales. The source of this large-scale variability and wind clumping in the winds of massive stars has not been established yet. At the same time, an increasing number of massive stars is found to have surface magnetic fields up to ~kG strength. Here we explore the incidence of a radiation-magnetohydrodynamic (MHD) instability that affects compressible MHD waves in the outer layers of massive stars with radiative envelopes. Using a stellar evolution code, we show that the instability should be present in most stars having radiative envelopes, with estimated saturation amplitudes that make this process a plausible source of the sub-photospheric variability required to account for observations. [Preview Abstract] |
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