Horizons in the near-equilibrium regime

Abstract: Quasi-static systems are an important concept in thermodynamics: they are dynamic but close enough to equilibrium that many properties of equilibrium systems still hold. Slowly evolving horizons are the corresponding concept for quasilocally defined black holes: they are "nearly isolated" future outer trapping horizons. This article reviews the definition and properties of these objects including both their mechanics and the role that they play in the fluid-gravity correspondence. It also introduces a new property: there is an event horizon candidate in close proximity to any slowly evolving horizon.