Denef, FrederikMoore, Gregory W.2009-07-022007Denef, Frederik, and Gregory W. Moore. 2007. How many black holes fit on the head of a pin? General Relativity and Gravitation 39(10): 1539-1544.0001-7701http://nrs.harvard.edu/urn-3:HUL.InstRepos:3138326The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered configurations.en-US10.1007/s10714-007-0469-4