  Energy released by a small fraction of the baryons in the universe, which
condensed out of while the IGM was cold, dark, and neutral,reheated and
reionized it, exposing gas clouds within it to the glare of ionizing radiation.
The first gas dynamical simulations of the photoevaporation of an intergalactic
cloud by a quasar, including radiative transfer, are presented, along with a
few observational diagnostics.

Astrophysics