3 research outputs found
A fully covariant mean-field dynamo closure for numerical 3+1 resistive GRMHD
The powerful high-energy phenomena typically encountered in astrophysics
invariably involve physical engines, like neutron stars and black hole
accretion disks, characterized by a combination of highly magnetized plasmas,
strong gravitational fields, and relativistic motions. In recent years
numerical schemes for General Relativistic MHD (GRMHD) have been developed to
model the multidimensional dynamics of such systems, including the possibility
of an evolving spacetime. Such schemes have been also extended beyond the ideal
limit including the effects of resistivity, in an attempt to model dissipative
physical processes acting on small scales (sub-grid effects) over the global
dynamics. Along the same lines, magnetic fields could be amplified by the
presence of turbulent dynamo processes, as often invoked to explain the high
values of magnetization required in accretion disks and neutron stars. Here we
present, for the first time, a further extension to include the possibility of
a mean-field dynamo action within the framework of numerical 3+1 (resistive)
GRMHD. A fully covariant dynamo closure is proposed, in analogy with the
classical theory, assuming a simple alpha-effect in the comoving frame. Its
implementation into a finite-difference scheme for GRMHD in dynamical
spacetimes [the X-ECHO code: (Bucciantini and Del Zanna 2011)] is described,
and a set of numerical test is presented and compared with analytical solutions
wherever possible.Comment: 16 pages, 11 figures, accepted for publication in MNRA