BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI

Journal Article · Mon Mar 01 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/711/1/50· OSTI ID:21394392

Tchekhovskoy, Alexander; Narayan, Ramesh ^[1]

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1. Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

Radio loud active galactic nuclei (AGNs) are on average 1000 times brighter in the radio band compared to radio quiet AGNs. We investigate whether this radio loud/quiet dichotomy can be due to differences in the spin of the central black holes (BHs) that power the radio-emitting jets. Using general relativistic magnetohydrodynamic simulations, we construct steady state axisymmetric numerical models for a wide range of BH spins (dimensionless spin parameter 0.1 <= a <= 0.9999) and a variety of jet geometries. We assume that the total magnetic flux through the BH horizon at radius r{sub H}(a) is held constant. If the BH is surrounded by a thin accretion disk, we find that the total BH power output depends approximately quadratically on the angular frequency of the hole, P {proportional_to} OMEGA{sup 2}{sub H} {proportional_to} (a/r{sub H}){sup 2}. We conclude that, in this scenario, differences in the BH spin can produce power variations of only a few tens at most. However, if the disk is thick such that the jet subtends a narrow solid angle around the polar axis, then the power dependence becomes much steeper, P {proportional_to} OMEGA{sup 4}{sub H} or even {proportional_to}OMEGA{sup 6}{sub H}. Power variations of 1000 are then possible for realistic BH spin distributions. We derive an analytic solution that accurately reproduces the steeper scaling of jet power with OMEGA{sub H} and we provide a numerical fitting formula that reproduces all our simulation results. We discuss other physical effects that might contribute to the observed radio loud/quiet dichotomy of AGNs.

• OSTI ID: 21394392
• Journal Information: Astrophysical Journal, Vol. 711, Issue 1; Other Information: DOI: 10.1088/0004-637X/711/1/50; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
ANALYTICAL SOLUTION
AXIAL SYMMETRY
BLACK HOLES
GALAXIES
GALAXY NUCLEI
GEOMETRY
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
QUASARS
RELATIVISTIC RANGE
SIMULATION
SPIN
STEADY-STATE CONDITIONS
ANGULAR MOMENTUM
COSMIC RADIO SOURCES
ENERGY RANGE
FLUID MECHANICS
HYDRODYNAMICS
MATHEMATICAL SOLUTIONS
MATHEMATICS
MECHANICS
PARTICLE PROPERTIES
SYMMETRY