Horizons in matter: Black hole hair versus null big bang

It is shown that only particular kinds of matter (in terms of the 'radial' pressure-to-density ratio w) can coexist with Killing horizons in black hole or cosmological spacetimes. Thus, for arbitrary (not necessarily spherically symmetric) static black holes, admissible are vacuum matter (w = -1, i.e. the cosmological constant or its generalization with the same value of w) and matter with certain values of w between 0 and -1, in particular a gas of disordered cosmic strings (w = -1/3). If the cosmological evolution starts from a horizon (the so-called null big bang scenarios), this horizon can coexist with vacuum matter and certain kinds of phantom matter with w ≤ -3. It is concluded that normal matter in such scenarios is entirely created from vacuum. © 2009 World Scientific Publishing Company.