Penrose diagram for a transient black hole

A Penrose diagram is constructed for a spatially coherent black hole that smoothly begins an accretion, and then excretes symmetrically as measured by a distant observer, with the initial and final states described by a metric of the Minkowski form. Coordinate curves on the diagram are computationally derived. Causal relationships between spacetime regions are briefly discussed. The life cycle of the black hole demonstrably leaves asymptotic observers in an unaltered Minkowski spacetime of uniform conformal scale.