  The morphology of a mixture made of a polar active gel immersed in an
isotropic passive fluid is studied numerically. Lattice Boltzmann method is
adopted to solve the Navier-Stokes equation and coupled to a finite-difference
scheme used to integrate the dynamic equations of the concentration and of the
polarization of the active component. By varying the relative amounts of the
mixture phases, different structures can be observed. In the contractile case,
at moderate values of activity, elongated structures are formed when the active
component is less abundant, while a dynamic emulsion of passive droplets in an
active matrix is obtained for symmetric composition. When the active component
is extensile, aster-like rotating droplets and a phase-separated pattern appear
for asymmetric and symmetric mixtures, respectively. The relevance of space
dimensions in the overall morphology is shown by studying the system in three
dimensions in the case of extensile asymmetric mixtures where interconnected
tube-like structures span the whole system.
