Abstract
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 space–times. 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.
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