In the presence of a strong magnetic field, accretion discs surrounding neutron stars, black holes, and white dwarfs have their inner edges at their Alfvén radii, i.e., at the distance where magnetic energy densi...In the presence of a strong magnetic field, accretion discs surrounding neutron stars, black holes, and white dwarfs have their inner edges at their Alfvén radii, i.e., at the distance where magnetic energy density becomes equal to the kinetic energy density. Young stars, X-ray binaries, active galactic nuclei possess discs which could generate jets. Jets arise at the inner boundary of the disc at the Alfvén radius when magnetic field is sufficiently strong. We emphasize here that not only accretion discs possess this feature. The inner edge of the heliospheric current sheet is located at the solar Alfvén radius. The inner edges of the Jovian magnetodisc and Saturnian ring current are also placed close to their Alfvén radii. Thus, in the presence of a strong magnetic field the inner edges of a lot of astrophysical discs are located at Alfvén radii regardless of the nature of their origin, material, and motion direction. This means that discs under such conditions are well described by MHD theory.展开更多
文摘In the presence of a strong magnetic field, accretion discs surrounding neutron stars, black holes, and white dwarfs have their inner edges at their Alfvén radii, i.e., at the distance where magnetic energy density becomes equal to the kinetic energy density. Young stars, X-ray binaries, active galactic nuclei possess discs which could generate jets. Jets arise at the inner boundary of the disc at the Alfvén radius when magnetic field is sufficiently strong. We emphasize here that not only accretion discs possess this feature. The inner edge of the heliospheric current sheet is located at the solar Alfvén radius. The inner edges of the Jovian magnetodisc and Saturnian ring current are also placed close to their Alfvén radii. Thus, in the presence of a strong magnetic field the inner edges of a lot of astrophysical discs are located at Alfvén radii regardless of the nature of their origin, material, and motion direction. This means that discs under such conditions are well described by MHD theory.
