ACCELERATION AND COLLIMATION OF RELATIVISTIC MAGNETOHYDRODYNAMIC DISK WINDS
- Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)
We perform axisymmetric relativistic magnetohydrodynamic simulations to investigate the acceleration and collimation of jets and outflows from disks around compact objects. Newtonian gravity is added to the relativistic treatment in order to establish the physical boundary condition of an underlying accretion disk in centrifugal and pressure equilibrium. The fiducial disk surface (respectively a slow disk wind) is prescribed as boundary condition for the outflow. We apply this technique for the first time in the context of relativistic jets. The strength of this approach is that it allows us to run a parameter study in order to investigate how the accretion disk conditions govern the outflow formation. Substantial effort has been made to implement a current-free, numerical outflow boundary condition in order to avoid artificial collimation present in the standard outflow conditions. Our simulations using the PLUTO code run for 500 inner disk rotations and on a physical grid size of 100 x 200 inner disk radii. The simulations evolve from an initial state in hydrostatic equilibrium and an initially force-free magnetic field configuration. Two options for the initial field geometries are applied-an hourglass-shaped potential magnetic field and a split monopole field. Most of our parameter runs evolve into a steady state solution which can be further analyzed concerning the physical mechanism at work. In general, we obtain collimated beams of mildly relativistic speed with Lorentz factors up to 6 and mass-weighted half-opening angles of 3-7 deg. The split-monopole initial setup usually results in less collimated outflows. The light surface of the outflow magnetosphere tends to align vertically-implying three relativistically distinct regimes in the flow-an inner subrelativistic domain close to the jet axis, a (rather narrow) relativistic jet and a surrounding subrelativistic outflow launched from the outer disk surface-similar to the spine-sheath structure currently discussed for asymptotic jet propagation and stability. The outer subrelativistic disk-wind is a promising candidate for the X-ray absorption winds that are observed in many radio-quiet active galactic nuclei. The hot winds under investigation acquire only low Lorentz factors due to the rather high plasma-beta we have applied in order to provide an initial force-balance in the disk corona. When we increase the outflow Poynting flux by injecting an additional disk toroidal field into the outflow, the jet velocities achieved are higher. These flows gain super-magnetosonic speed and remain Poynting flux dominated.
- OSTI ID:
- 21392288
- Journal Information:
- Astrophysical Journal, Vol. 709, Issue 2; Other Information: DOI: 10.1088/0004-637X/709/2/1100; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
BIPOLAR JETS LAUNCHED FROM MAGNETICALLY DIFFUSIVE ACCRETION DISKS. I. EJECTION EFFICIENCY VERSUS FIELD STRENGTH AND DIFFUSIVITY
Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo
Related Subjects
COSMOLOGY AND ASTRONOMY
ABSORPTION
ACCELERATION
ACCRETION DISKS
AXIAL SYMMETRY
BOUNDARY CONDITIONS
FORCE-FREE MAGNETIC FIELDS
GALAXIES
GALAXY NUCLEI
GRAVITATION
MAGNETOHYDRODYNAMICS
MONOPOLES
PLUTO PLANET
RELATIVISTIC RANGE
ROTATION
SIMULATION
STEADY-STATE CONDITIONS
X RADIATION
ELECTROMAGNETIC RADIATION
ENERGY RANGE
FLUID MECHANICS
HYDRODYNAMICS
IONIZING RADIATIONS
MAGNETIC FIELDS
MECHANICS
MOTION
PLANETS
RADIATIONS
SORPTION
SYMMETRY