The evolution of a force-free granular gas with a constant restitution coefficient isstudied by means of granular hydrodynamics. We numerically solve the hydrodynamicequations and analyze the mechanisms of cluster formation. According to our findings, thepresently accepted mode-enslaving mechanism may not be responsible for the latterphenomenon. On the contrary, we observe that the cluster formation is mainly driven byshock-waves, which spontaneously originate and develop in the system. This agrees with apreviously suggested mechanism of formation of density singularities in one-dimensionalgranular gases.
