Astronomy and Astrophysics – Astrophysics
Scientific paper
1993-09-28
Astronomy and Astrophysics
Astrophysics
11 pages aastex astro-ph/yymmnnn 4
Scientific paper
I review recent work on the radial transport of angular momentum in ionized, Keplerian accretion disks. Proposed mechanisms include hydrodynamic and MHD local instabilities and long range effects mediated by wave transport. The most promising models incorporate the Velikhov-Chandrasekhar instability, caused by an instability of the magnetic field embedded in a differentially rotating disk. This has the important feature that the induced turbulent motions necessarily transport angular momentum outward. By contrast, convective modes may transport angular momentum in either direction. Combining the magnetic field instability with an $\alpha-\Omega$ dynamo driven by internal waves leads to a model in which the dimensionless viscosity scales as $(H/r)^{4/3}$. However, this model has a phenomenology which is quite different from the $\alpha$ disk model. For example, an active disk implies some source of excitation for the internal waves. In binary systems with a mass ratio of order unity the most likely exciting mechanism is a parametric instability due to tidal forces. This implies that in systems where the accretion stream is intermittent, like MV Lyrae or TT Ari, epochs when the mass flow is absent or very small will be epochs in which the disk shrinks and becomes relatively inactive and dark. This model also implies that forced vertical mixing is important, even in convectively stable disks. I discuss various observational tests of this model and the focus of current theoretical work.
No associations
LandOfFree
Why Disks Shine: the Transport of Angular Momentum in Hot, Thin Disks does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Why Disks Shine: the Transport of Angular Momentum in Hot, Thin Disks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Why Disks Shine: the Transport of Angular Momentum in Hot, Thin Disks will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-370999