Magnetic field lines and current sheets for an orbiting neutron star binary with the magnetic moment of one star
aligned with the rotation axis, and the magnetic moment of the
other star tilted and antialigned with the rotation axis. The
stars are spinning rapidly at ∼ ms periods, with R_{LC,∗} /R_∗ =
2.7.
Stellar spin winds fields backwards toroidally.
This movie shows the corotating field pattern as the orbit progresses.
This movie shows the dynamical behavior of field lines seeded on one of the stars. We find
a clear cyclical process operating in the magnetosphere. First, field lines from one star can attach to the second star. Second, as the orbit progresses these field lines
develop twist and are expelled outward past the second
star as closed loops. Third, these loops open up to infinity and then reconnect on the far side of the first star
opposite to the second. Fourth, the orbital motion will
bring the second star back into contact with the closed
loops, and they reattach to the second star.
The Magnetospheric Multiscale (MMS) mission has given us unprecedented access to high cadence particle and field data of magnetic reconnection at Earth's magnetopause. MMS first passed very near an X-line on 16 October 2015, the Burch event, and has since observed multiple X-line crossings. Subsequent 3D particle-in-cell (PIC) modeling efforts of and comparison with the Burch event have revealed a host of novel physical insights concerning magnetic reconnection, turbulence induced particle mixing, and secondary instabilities. In this study, we employ the Gkeyll simulation framework to study the Burch event with different classes of extended, multi-fluid magnetohydrodynamics (MHD), including models that incorporate important kinetic effects, such as the electron pressure tensor, with physics-based closure relations designed to capture linear Landau damping. Such fluid modeling approaches are able to capture different levels of kinetic physics in global simulations and are generally less costly than fully kinetic PIC. We focus on the additional physics one can capture with increasing levels of fluid closure refinement via comparison with MMS data and existing PIC simulations. In particular, we find that the ten-moment model well captures the agyrotropic structure of the pressure tensor in the vicinity of the X-line and the magnitude of anisotropic electron heating observed in MMS and PIC simulations. However, the ten-moment model has difficulty resolving the lower hybrid drift instability, which has been observed to plays a fundamental role in heating and mixing electrons in the current layer.
Dust and starlight have been modeled for the KINGFISH project galaxies. For each pixel in each galaxy, we estimate: (1) dust surface density; (2) q_PAH, the dust mass fraction in PAHs; (3) distribution of starlight intensities heating the dust; (4) luminosity emitted by the dust; and (5) dust luminosity from regions with high starlight intensity. The modeling is as described in the paper "Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: The KINGFISH Sample", by G. Aniano, B.T. Draine, L.K. Hunt, K. Sandstrom, D. Calzetti, R.C. Kennicutt, D.A, Dale, and 26 other authors, accepted for publication in The Astrophysical Journal.
A subset of the Fermi-LAT public data for use with NPTFit:
https://github.com/bsafdi/NPTFit
The data here is for use with the Jupyter example notebooks provided with the
main code. Details of the files provided are given below. All files are provided
as numpy arrays binned as nside=128 HEALPix maps.
For the full public data, see:
http://fermi.gsfc.nasa.gov/ssc/data/access/
Dielectric tensor for crystalline graphite from X-ray to microwave frequencies, as discussed in the paper "Graphite Revisited" (Draine 2016, Astrophysical Journal, in press). Cross sections for absorption and scattering by graphite spheres and spheroids are also tabulated, as well as Planck-averaged cross sections for absorption and scattering of radiation with a Planck spectrum.
Force-driven parallel shear flow in a spatially periodic domain is shown to be linearly unstable
with respect to both the Reynolds number and the domain aspect ratio. This finding is confirmed
by computer simulations, and a simple expression is derived to determine stable flow conditions.
Periodic extensions of Couette and Poiseuille flows are unstable at Reynolds numbers two orders
of magnitude smaller than their aperiodic equivalents because the periodic boundaries impose
fundamentally different constraints. This instability has important implications for designing computational models of nonlinear dynamic processes with periodicity.
