Investigation on the origin of black-hole entropy

The entropy bound of a self-gravitating radiation system (SGRS) confined to a spherical box with a central black hole is calculated by using the modified equation of state of radiation near the black-hole horizon, which was derived by Li and Liu. A reasonable mode of the gravitational collapse of a SGRS is given, and the collapsing process is proved to be an entropy-increasing process, throughout which the upper bound on the entropy of the whole system is equal to the entropy of the final black hole with the same mass as the system. In this way, a possible explanation for the origin of black-hole entropy is provided, which is an extension of this author's previous work.