  The Dirac Hamiltonian including nuclear recoil and vacuum-polarization
operators is considered in a supercritical regime Z > 137. It is found that the
nuclear recoil operator derived within the Breit approximation regularizes the
Hamiltonian for the point-nucleus model and allows the ground state level to go
continuously down and reach the negative energy continuum at a critical value
Zcr = 145. If the Hamiltonian contains both the recoil operator and the Uehling
potential, the 1s level reaches the negative energy continuum at Zcr = 144. The
corresponding calculations for the excited states have been also performed.
This study shows that, in contrast to previous investigations, a point-like
nucleus can have effectively the charge Z > 137.
