ABSTRACT We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics using a direct Monte Carlo solution of the frequency-dependent ...radiative transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and to a slowly accreting Kerr black hole in axisymmetry.
We explore with self-consistent 2D F
ornax
simulations the dependence of the outcome of collapse on many-body corrections to neutrino-nucleon cross sections, the nucleon-nucleon bremsstrahlung rate, ...electron capture on heavy nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and neutrino-nucleon scattering. Importantly, proximity to criticality amplifies the role of even small changes in the neutrino-matter couplings, and such changes can together add to produce outsized effects. When close to the critical condition the cumulative result of a few small effects (including seeds) that individually have only modest consequence can convert an anemic into a robust explosion, or even a dud into a blast. Such sensitivity is not seen in one dimension and may explain the apparent heterogeneity in the outcomes of detailed simulations performed internationally. A natural conclusion is that the different groups collectively are closer to a realistic understanding of the mechanism of core-collapse supernovae than might have seemed apparent.
Pair Production in Low-luminosity Galactic Nuclei Mościbrodzka, M; Gammie, C. F; Dolence, J. C ...
Astrophysical journal/The Astrophysical journal,
07/2011, Letnik:
735, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Electron-positron pairs may be produced near accreting black holes by a variety of physical processes, and the resulting pair plasma may be accelerated and collimated into a relativistic jet. Here, ...we use a self-consistent dynamical and radiative model to investigate pair production by Delta *g Delta *g collisions in weakly radiative accretion flows around a black hole of mass M and accretion rate . Our flow model is drawn from general relativistic magnetohydrodynamic simulations, and our radiation field is computed by a Monte Carlo transport scheme assuming the electron distribution function is thermal. We argue that the pair production rate scales as . We confirm this numerically and calibrate the scaling relation. This relation is self-consistent in a wedge in parameter space. If is too low the implied pair density over the poles of the black hole is below the Goldreich-Julian density and Delta *g Delta *g pair production is relatively unimportant; if is too high the models are radiatively efficient. We also argue that for a power-law spectrum the pair production rate should scale with the observables LX = X-ray luminosity and M as L 2 X M --4. We confirm this numerically and argue that this relation likely holds even for radiatively efficient flows. The pair production rates are sensitive to black hole spin and to the ion-electron temperature ratio which are fixed in this exploratory calculation. We finish with a brief discussion of the implications for Sgr A* and M87.
We present the galaxy two-point angular correlation function for galaxies selected from the seventh data release of the Sloan Digital Sky Survey (SDSS). The galaxy sample was selected with r-band ...apparent magnitudes between 17 and 21, and we measure the correlation function for the full sample as well as for the four magnitude ranges: 17-18, 18-19, 19-20 and 20-21. We update the flag criteria to select a clean galaxy catalogue and detail specific tests that we perform to characterize systematic effects, including the effects of seeing, Galactic extinction and the overall survey uniformity. Notably, we find that optimally we can use observed regions with seeing <1.5 arcsec, and r-band extinction <0.13 mag, smaller than previously published results. Furthermore, we confirm that the uniformity of the SDSS photometry is minimally affected by the stripe geometry. We find that, overall, the two-point angular correlation function can be described by a power law, ω(θ) = A
ωθ(1 − γ) with γ 1.72, over the range 0
005-10°. We also find similar relationships for the four magnitude subsamples, but the amplitude within the same angular interval for the four subsamples is found to decrease with fainter magnitudes, in agreement with previous results. We find that the systematic signals are well below the galaxy angular correlation function for angles less than approximately 5°, which limits the modelling of galaxy angular correlations on larger scales. Finally, we present our custom, highly parallelized two-point correlation code that we used in this analysis.
Transition and turbulence decay with the Taylor–Green vortex have been effectively used to demonstrate emulation of high Reynolds-number (Re) physical dissipation through numerical convective effects ...of various non-oscillatory finite-volume algorithms for implicit large eddy simulation (ILES), e.g. using the Godunov-based Eulerian adaptive mesh refinement code xRAGE. The inverse-chevron shock tube experiment simulations have been also used to assess xRAGE based ILES for shock driven turbulent mixing, compared with available simulation and laboratory data. The previous assessments are extended to evaluate new directionally-unsplit high-order algorithms in xRAGE, including a correction to address the well-known issue of excessive numerical diffusion of shock-capturing (e.g., Godunov-type) schemes for low Mach numbers. The unsplit options for hydrodynamics in xRAGE are discussed in detail, followed by fundamental tests with representative shock problems. Basic issues of transition to turbulence and turbulent mixing are discussed, and results of simulations of high-Re turbulent flow and mixing in canonical test cases are reported. Compared to the directional-split cases, and for each grid resolution considered, unsplit results exhibit transition to turbulence with much higher effective Re—and significantly more so with the low Mach number correction.
THE GALACTIC CENTER WEATHER FORECAST MOSCIBRODZKA, M; Shiokawa, H; Gammie, C F ...
Astrophysical journal. Letters,
06/2012, Letnik:
752, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In accretion-based models for Sgr A*, the X-ray, infrared, and millimeter emission arise in a hot, geometrically thick accretion flow close to the black hole. The spectrum and size of the source ...depend on the black hole mass accretion rate M. Since Gillessen et al. have recently discovered a cloud moving toward Sgr A* that will arrive in summer 2013, M may increase from its present value M sub(0). We therefore reconsider the "best-bet" accretion model of Moscibrodzka et al., which is based on a general relativistic MHD flow model and fully relativistic radiative transfer, for a range of M. We And that for modest increases in M the characteristic ring of emission due to the photon orbit becomes brighter, more extended, and easier to detect by the planned Event Horizon Telescope submillimeter Very Long Baseline Interferometry experiment. If M > ~ 8 M sub(0), this "silhouette" of the black hole will be hidden beneath the synchrotron photosphere at 230 GHz, and for M > ~ 16 M sub(0) the silhouette is hidden at 345 GHz. We also And that for M > 2 M sub(0) the near-horizon accretion flow becomes a persistent X-ray and mid-infrared source, and in the near-infrared Sgr A* will acquire a persistent component that is brighter than currently observed flares.
Summary
Evidence suggests that aging, per se, is a major risk factor for cardiac dysfunction. Oxidative modification of cardiac proteins by non‐enzymatic glycation, i.e. advanced glycation ...endproducts (AGEs), has been implicated as a causal factor in the aging process. This study was designed to examine the role of aging on cardiomyocyte contractile function, cardiac protein oxidation and oxidative modification. Mechanical properties were evaluated in ventricular myocytes from young (2‐month) and aged (24–26‐month) mice using a MyoCam® system. The mechanical indices evaluated were peak shortening (PS), time‐to‐PS (TPS), time‐to‐90% relengthening (TR90) and maximal velocity of shortening/relengthening (± dL/dt). Oxidative stress and protein damage were evaluated by glutathione and glutathione disulfide (GSH/GSSG) ratio and protein carbonyl content, respectively. Activation of NAD(P)H oxidase was determined by immunoblotting. Aged myocytes displayed a larger cell cross‐sectional area, prolonged TR90, and normal PS, ± dL/dt and TPS compared with young myocytes. Aged myocytes were less tolerant of high stimulus frequency (from 0.1 to 5 Hz) compared with young myocytes. Oxidative stress and protein oxidative damage were both elevated in the aging group associated with significantly enhanced p47phox but not gp91phox expression. In addition, level of cardiac AGEs was ∼2.5‐fold higher in aged hearts than young ones determined by AGEs‐ELISA. A group of proteins with a molecular range between 50 and 75 kDa with pI of 4–7 was distinctively modified in aged heart using one‐ or two‐dimension SDS gel electrophoresis analysis. These data demonstrate cardiac diastolic dysfunction and reduced stress tolerance in aged cardiac myocytes, which may be associated with enhanced cardiac oxidative damage, level of AGEs and protein modification by AGEs.
We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics using a direct Monte Carlo solution of the frequency-dependent radiative ...transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and to a slowly accreting Kerr black hole in axisymmetry.
The 2017 detection of the inspiral and merger of two neutron stars in gravitational waves and gamma rays was accompanied by a quickly reddening transient. Such a transient was predicted to occur ...following a rapid neutron capture (r-process) nucleosynthesis event, which synthesizes neutron-rich, radioactive nuclei and can take place in both dynamical ejecta and in the wind driven off the accretion torus formed after a neutron star merger. We present the first three-dimensional general relativistic, full transport neutrino radiation magnetohydrodynamics simulations of the black hole-accretion disk-wind system produced by the GW170817 merger. We show that the small but non-negligible optical depths lead to neutrino transport globally coupling the disk electron fraction, which we capture by solving the transport equation with a Monte Carlo method. The resulting absorption drives up the electron fraction in a structured, continuous outflow, with electron fraction as high as Ye∼0.4 in the extreme polar region. We show via nuclear reaction network and radiative transfer calculations that nucleosynthesis in the disk wind will produce a blue kilonova.
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