Microstates of Non-extremal Black Holes: A New Hope

We provide a new roadmap for constructing microstates of non-extremal black holes in supergravity. First, we review the non-linear sigma model of five-dimensional supergravity governing stationary solutions with a U(1) isometry and present the first generalized Ernst formulation of this model. We then revisit solution-generating techniques associated to the coset model symmetry, Ernst formalism and inverse scattering method. While some of these techniques have been extensively used to generate non-extremal black holes and black rings in supergravity, we demonstrate how they can be adapted to construct systematically non-BPS smooth horizonless geometries that have the same mass and charges as non-extremal black holes. To illustrate these methods, we construct novel static solutions of this type, including a non-BPS generalization of the $\frac{1}{2}$-BPS Gibbons-Hawking center, which has served as the fundamental building block of multicenter microstates of BPS black holes.