The corotation radius is another important characteristic of a magnetic
rotator. Suppose that an accreting plasma penetrates the light cylinder
and is stopped by the magnetic field at a certain distance
given by the balance between the static magnetic field pressure and the
plasma pressure. Suppose that the plasma is ``frozen'' in the rotator's
magnetic field. This field will drag the plasma and force it to rotate
rigidly with the angular velocity of the star. The matter will fall on
to the stellar surface only if its rotational velocity is smaller than
the Keplerian velocity at the given distance
:

Otherwise, a centrifugal barrier emerges and the rapidly rotating magnetic
field impedes the accretion of matter (Schwartzman, 1970a[173];
Pringle and Rees, 1972[164];
Davidson and Ostriker, 1973[38];
Lamb et al., 1973[93]; Illarionov
and Sunyaev, 1975[76]). The latter
authors assumed that if
, the magnetic field throws the plasma back beyond the capture radius.
They called this effect the ``propeller'' regime. In
fact, matter may not be shed (Lipunov 1980, 1982d[97,
101]), but it is important to note that
a stationary accretion is also not possible.

The corotation radius is thus defined as

where P is the rotational period of the star.

If
, rotation influences the accretion insignificantly. Otherwise, a stationary
accretion is not possible for
.