Question

Can a black hole be a gigantic string? If so, can a it be a enlarged extra dimensional structure inside, something is expanded under the energy in the black hole?

Answer 1

There is exist an opinion, confirmed by some calculations, that the black hole is not singular, it consists of the strings connected in some way. Such object is called a fuzzball. The number of connection options (the organization) of strings in such a structure is equal to the entropy of a black hole (obtained recently), and the dimensions are identical with the radius of the Event horizon (also a well-known concept).