On an effect in the problem of an expanding shell in relativistic gravity theory

It is shown that the Birkgoff theory, considered as the theorem on inevitable static character of any spherically-symmetric gravitational field in relativistic gravity theory (RGT), is not compiled with. The absence of the Birkgoff theorem in RGT results in new gravitational effects. In particular, using the example of problem on radially moving Δ-shaped shell, in which a sample body is placed, it is shown, that the body will be pulled to the geometric centre of the shell both in case of its expansion and compression. If the sample body initially rests at a certain small but finite distance from the shell centre, later on it will shift precisely to geometric centre of the shell