Kerr and Kerr-AdS Black Shells and Black Hole Entropy: An Operational Approach

As an operational approach to the Bekenstein-Hawking formula S_{BH}=A/4l_{Pl}^{2} for the black hole entropy, considered in this monograph is the reversible contraction of a spinning thin shell to its event horizon and it is found that the shell's thermodynamic entropy approaches S_{BH}. In this sense the shell, called a "black shell", imitates and is externally indistinguishable from a black hole. This work is a generalization of the previous result for the spherical case. The exterior space-time of the shell is assumed to be given by the Kerr metric and matched to two different interior metrics, a vacuum one and a non-vacuum one. The vacuum interior embedding is found to break down for fast spinning shells. The mechanism is not clear and worth further exploring. The case of a Kerr-AdS exterior is also examined, without trying to find a detailed interior solution. One should expect the same behavior of the shell when the horizon limit is approached.