In the 1990s, Joseph Polchinski discovered that the theory requires higher-dimensional objects, called D-branes and identified these with the black-hole solutions of supergravity.
V 90-tych rokoch, Joseph Polchinski zistil, že teória potrebuje vyššiedimenzionálne objekty, zvané D-brány a identifikoval ich s riešeniami supergravitácie čierne diery.