Dynamo-generated Turbulence and Outtows from Accretion Discs
نویسنده
چکیده
Local hydromagnetic simulations of accretion disc turbulence provide now the most convincing evidence that the origin of turbulence in discs could be the Balbus{Hawley magneto-rotational instability. The main results of such calculations are highlighted with particular emphasis on the generation of large scale magnetic elds. Comparison with mean-eld dynamo theory is made. This theory is then used to address the question of the launching and collimation of winds emanating from the disc surfaces.
منابع مشابه
Dynamo-generated turbulence and outflows from accretion discs
Local hydromagnetic simulations of accretion-disc turbulence currently provide the most convincing evidence that the origin of turbulence in discs could be the Balbus{ Hawley magnetorotational instability. The main results of such calculations are highlighted with particular emphasis on the generation of large-scale magnetic elds. Comparison with mean- eld dynamo theory is made. This theory ...
متن کاملThe dependence of the viscosity in accretion discs on theshear /
We estimate the Shakura-Sunyaev viscosity parameter alpha for diierent values of the shear/vorticity ratio, =!, using local simulations of dynamo-generated turbulence. We nd that the time average of is approximately proportional to =! (at least for =! < 10). We point out that this result may have important implications for the properties of thick accretion discs, because there ! is small and wo...
متن کاملThe dependence of the viscosity in accretion discs
We estimate the Shakura-Sunyaev viscosity parameter alpha for diierent values of the shear/vorticity ratio, =!, using local simulations of dynamo-generated turbulence. We nd that the time average of is approximately proportional to =! (at least for =! < 10). We point out that this result may have important implications for the properties of thick accretion discs, because there ! is small and wo...
متن کاملBlack hole accretion discs: reality confronts theory
Disc spectra from highly luminous black hole binaries are observed to be rather simple, despite theoretical predictions to the contrary. We collate the disc-dominated spectra from multiple observations of 10 separate sources, and show that these overwhelmingly follow a multi-temperature disc blackbody spectrum with luminosity∝ T , and that such discs are stable. These results are in conflict wi...
متن کاملHigh accretion rates in magnetised Keplerian discs mediated by a Parker instability driven dynamo
Hydromagnetic stresses in accretion discs have been the subject of intense theoretical research over the past one and a half decades. Most of the disc simulations have assumed a small initial magnetic field and studied the turbulence that arises from the magnetorotational instability. However, gaseous discs in galactic nuclei and in some binary systems are likely to have significant initial mag...
متن کامل