  It is shown that the energy in the centre of mass frame of two colliding
particles in free fall at any point of the ergosphere of the rotating black
hole can grow without limit for fixed energy values of particles on infinity.
The effect takes place for large negative values of the angular momentum of one
of the particles. It occurs that the geodesics with negative energy in
equatorial plane of rotating black holes cannot originate or terminate inside
the ergosphere. Their length is always finite and this leads to conclusion that
they must originate and terminate inside the gravitational radius of the
ergosphere. The energy in the centre of mass frame of one particle falling into
the gravitational radius and the other arriving from the area inside it is
growing without limit on the horizon.
