An Event Horizon 'Firewall' Undergoing Cosmological Expansion

We embed an object with a singular horizon structure, reminiscent of (but fundamentally different from, except in a limiting case) a black-hole event horizon, in an expanding, spherically symmetric, homogeneous, Universe that has a positive cosmological constant. Conformal representation is discussed. There is a temperature/pressure singularity and a corresponding scalar curvature singularity at the horizon. The expanding singular horizon ultimately bounds the entire space-time manifold. It is is preceded by an expanding light front, which separates the space-time affected by the singularity from that which is not yet affected. An appropriately located observer in front of the light front can have a Hubble-Lema\^itre constant that is consistent with that currently observed.