  We obtain an expression for the energy of the density wave propagating in a
multicomponent gravitating medium in the form well known from electrodynamics.
Using the above, the possibility of "triple production" of the quasi-particles,
or waves, with their energies summing up to zero, in a non-equilibrium medium
is demonstrated. That kind of resonance wave interaction is shown to result in
the development of an explosion instability. By the method developed in plasma
physics, the characteristic time of the instability is evaluated.
