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RISS 인기검색어
- 검색키워드
- 저자 : Ethan Vishniac (검색결과 3 건)
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The Corona-Dynamo Connetion in Accretion Disks
Ethan Vishniac 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
The theory of mean-eld dynamos in accretion disks has been discussed at length in numerous papers, dating back almost to the rst theoretical papers on accretion disks. In the last decade the theory of mean-eld dynamos in almost perfectly conducting uids has been subjected to strong criticisms, based on general theoretical considerations and as well as numerical tests. Paradoxically, the numerical evidence for mean-eld dynamo activity in accretion disks, driven by the magnetorotational instability (MRI), has become extremely strong. I will discuss a reformulation of mean- eld dynamo theory, based on magnetic helicity conservation, which is consistent with previous theoretical and numerical analyses. Applying this to accretions disks, we nd that the MRI drives a magnetic helicity current aligned with the spin axis of the disk. As this current emerges into the disk corona it is carried by magnetic structures of steadily increasing size. Consequently the energy ux associated with the magnetic helicity current drops, leading to the dissipation of energy in the corona. This represents a minimal level of coronal heating A similar dynamo operating in the collisionless plasma of the corona can produce additional coronal heating, in which case the magnetic helicity current driven by the corona will increase the eciency of the disk dynamo.
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MAGNETIC FIELDS IN STARS AND DISKS
VISHNIAC ETHAN T. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
Magnetic fields are thought to playa role in a wide variety of important astrophysical processes, from angular momentum transport and jet formation in accretion disks to corona formation in stars. Unfortunately, the dynamics of magnetic fields in astrophysical plasmas are extremely complicated, and the success of current theoretical models and computer simulations seems to be inversely correlated with the amount of observational detail available to us. Here I will discuss some of the more striking conflicts between numerical simulations and observations, and present an explanation for them based on an important dynamical process which is not adequately modeled in current numerical simulations. These processes will lead to the formation of flux tubes in stars and accretion disks, in accordance with observations. I will discuss some of the implications of flux tube formation for stellar and accretion disk dynamos.
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ScienceON
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