The Geometry of Black Hole Microstructure

String Theory is famous for its ability to count the degrees of freedom that give the entropy of supersymmetric black holes, but this counting is always done in a regime of parameters where the gravitational interactions are turned off. This leaves open the question of how these microscopic degrees of freedom look like in the regime of parameters where the classical black hole solution exists, and in my talk I will address this question for the M2-M5-P black hole, whose entropy at weak coupling comes from M2-branes fractionating into strips between parallel M5-branes. I will show that the backreaction of these strips forms a complicated structure, the “Supermaze”, which preserves four supercharges globally but sixteen locally. Inspired by this, I will argue that black hole microstate structure should be described by “Themelia”, brane configurations with 1/2-BPS local supersymmetry enhancement, and I will argue that the associated supergravity solutions should be horizonless. Finally, I will present progress towards building the Supermaze supergravity solutions.