Аннотация:The accreting ionized gas surrounding a neutron star or white dwarf creates an accretion disc. Radius R A (the Alfven radius), where the magnetic energy density is equal to the kinetic energy density is an inner boundary of a disc. Accretion disc in a binary system and around a black hole is disrupted at a radius R A (the Alfven radius), where the magnetic energy density is equal to the kinetic energy density is an inner boundary of a disc. Accretion disc in a binary system and around a black hole is disrupted at a radius R A . The heliospheric current sheet’s inner edge is also located at the solar Alfven radius. The inner edges of the Jupiter and Saturn discs are located close to their Alfven radii determined by the plasma azimuthal velocities. Due to the star-exoplanet interaction, a magnetosphere with a magnetodisc arises around the magnetized extrasolar planet placed in close orbit about the host star (“Hot Jupiter”). The distance to disc’s inner edge from the center of the host star is a key parameter of the exoplanet magnetospheric model. It determines the disc’s magnetic moment, and as a consequence, the total magnetospheric magnetic field and the character size of the magnetosphere. Here we discuss the exoplanet’s disc inner edge location at R A in a context of other astrophysical discs and emphasize that for definite parameters (existence of a strong magnetic field, for example) a lot of them also have location of their inner edges at the Alfven radii independent of nature of their origin, of the disc’s material, and of the motion direction in the disc, which means that a large class of discs is well described by the MHD theory.