  We study the homologous collapse of stellar nuclear core, the virial theorem
for hadron collisional relaxations, and photon productions from hadron
collisions. We thus show the gravo-thermal dynamical process that transforms
gravitational energy to photon energy. The process is energetically and
entropically favourable. The total baryon number conservation, Euler equation
for energy-momentum conservation and Poisson's equation for gravitational
potential are adopted to describe homologous core collapses. The virial theorem
determines the hadron collision energy gain from gravitational potential. The
hadronic photon production rate determines the photon energy density. The time
scales of macroscopic and microscopic processes are studied to verify
approximations. As a result, we show the formation of opaque photon-pair
spheres, whose total energy, size, temperature and number density, accounting
for the main energetic features of Gamma-Ray Burst progenitors. We obtain the
intrinsic correlations of these quantities. They depend only on the averaged
thermal index of the stellar core. We discuss the possibility to confront them
with observational data.
