RESUMEN
We propose a mechanism for the fast dissipation of magnetic fields which is effective in a stratified medium where ion motions can be neglected. In such a medium, the field is frozen into the electrons, and Hall currents prevail. Although Hall currents conserve magnetic energy, in the presence of density gradients they are able to create current sheets which can be sites for efficient dissipation of magnetic fields. We recover the frequency omega(MH) for Hall oscillations modified by the presence of density gradients. We show that these oscillations can lead to an exchange of energy between different components of the field. We calculate the time evolution, and show that magnetic fields can dissipate on a time scale of order 1/omega(MH). This mechanism can play an important role in magnetic dissipation in systems with very steep density gradients, where the ions are static such as those found in the solid crust of neutron stars.
RESUMEN
Spatially varying primordial magnetic fields may be efficiently dissipated prior to the epoch of recombination due to the large viscosity of the baryon-photon fluid. We show that this dissipation may result in observable chemical potential &mgr; and Compton y distortions in the cosmic microwave background spectrum. Current upper limits on &mgr; and y from FIRAS constrain magnetic fields to have strength B0<3x10(-8) G (scaled to the present) between comoving coherence length approximately 400 pc and approximately 0.6 Mpc. These represent the strongest upper limits on small-scale primordial magnetic fields to date.
RESUMEN
We study the spectral distortions of the cosmic microwave background radiation induced by the effect in clusters of galaxies when the target electrons have a modified Maxwell-Boltzmann distribution with a high-energy nonthermal tail. Bremsstrahlung radiation from this type of electron distribution may explain the suprathermal X-ray emission observed in some clusters such as the Coma Cluster and A2199 and serve as an alternative to the classical but problematic inverse Compton scattering interpretation. We show that the Sunyaev-Zeldovich effect can be used as a powerful tool to probe the electron distribution in clusters of galaxies and discriminate among these different interpretations of the X-ray excess. The existence of a nonthermal tail can have important consequences for cluster-based estimators of cosmological parameters.
RESUMEN
The long-held notion that the highest energy cosmic rays are of distant extragalactic origin is challenged by observations that events above approximately 1020 eV do not exhibit the expected high-energy cutoff from photopion production off the cosmic microwave background. We suggest that these unexpected ultra-high-energy events are due to iron nuclei accelerated from young strongly magnetized neutron stars through relativistic MHD winds. We find that neutron stars whose initial spin periods are shorter than approximately 10 ms and whose surface magnetic fields are in the 1012-1014 G range can accelerate iron cosmic rays to greater than approximately 1020 eV. These ions can pass through the remnant of the supernova explosion that produced the neutron star without suffering significant spallation reactions or energy loss. For plausible models of the Galactic magnetic field, the trajectories of the iron ions curve sufficiently to be consistent with the observed, largely isotropic arrival directions of the highest energy events.