Magnetic helicity in astrophysics

Conference · Mon Jun 30 04:00:00 EDT 1986 · AIP Conf. Proc.; (United States)

OSTI ID:6752668

Field, G

Magnetic helicity, which is conserved in ideal MHD, measures the linkage of magnetic lines of force. After a brief review, I consider the helicity of a stellar magnetic field and show that a modified definition of helicity, called relative helicity, enables one to compute the relative amount of linkage of two field configurations above the photosphere even though the subphotospheric field is unobservable. I also show how the relative helicity changes as the result of motions of photospheric material. Then I consider the dissipation of helicity and show that in certain situations it is dissipated much more slowly than magnetic energy. Finally, I propose a variational principle for static problems, and show that in the presence of finite pressure, helicity conservation yields the usual equation of magnetostatic equilibrium. Woltjer's conclusion that the result is a force-free field is a result of his neglect of pressure.

• Research Organization: Center for Astrophysics, Cambridge, Massachusetts 02138
• OSTI ID: 6752668
• Report Number(s): CONF-8408121-
• Conference Information: Journal Name: AIP Conf. Proc.; (United States) Journal Volume: 144:1
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
FLUID MECHANICS
HELICITY
HYDRODYNAMICS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MECHANICS
PARTICLE PROPERTIES
STARS
STELLAR ATMOSPHERES
STELLAR MAGNETOSPHERES