“…I recall how during my visits to Moscow in the middle of the 1970s Zel'dovich and his colleagues were somewhat regretfully admitting that they were on the edge of discovering the Hawking effect. They realized that an analogue of the Penrose process occurs with the waves (in so called superradiant scattering) which get amplified if their energy per unit angular momentum is smaller than the angular velocity 17 Relativists often consider the effects produced by moving mass currents as "the dragging of inertial frames", but the concept of the gravomagnetic field, or gravomagnetism has some advantages, as has been stressed recently [148]. The gravomagnetic viewpoint, however, has also been used in many works in the pastsee, e.g.…”