  We study the supercritical instability in gapped graphene with two charged
impurities separated by distance R using the two-dimensional Dirac equation for
electron quasiparticles. Attention is paid to a situation when charges of
impurities are subcritical, whereas their total charge exceeds a critical one.
The critical distance R_{cr} in the system of two charged centers is defined as
that at which the electron bound state with the lowest energy reaches the
boundary of the lower continuum. A variational calculation of the critical
distance R_{cr} separating the supercritical (R<R_{cr}) and subcritical
(R>R_{cr}) regimes is carried out. It is shown that the critical distance
R_{cr} increases as the quasiparticle gap decreases. The energy and width of a
quasistationary state as functions of the distance between two impurities are
derived in the quasiclassical approximation.
