Active nematics are intrinsically phase-separated

Two-dimensional nonequilibrium nematic steady states, as found in agitated granular-rod monolayers or films of orientable amoeboid cells, were predicted [Europhys. Lett. {\bf 62} (2003) 196] to have giant number fluctuations, with standard deviation proportional to the mean. We show numerically that the steady state of such systems is {\em macroscopically phase-separated}, yet dominated by fluctuations, as in the Das-Barma model [PRL {\bf 85} (2000) 1602]. We suggest experimental tests of our findings in granular and living-cell systems.