Relativistic extended thermodynamics of rarefied polyatomic gas

The goal of the present paper is to construct a relativistic extended thermodynamics (ET) theory of rarefied polyatomic gases. This is achieved by adopting the closure procedure for the 14 generalized moments of a distribution function that, as in the classical case, depends on an additional continuous variable representing the energy of the internal modes of a molecule. This permits the theory to take into account the energy exchange between translational modes and internal modes of a molecule in binary collisions. The theory includes the ET theory of monatomic gases as a singular limit and converges to the corresponding ET theory of polyatomic gases in the classical limit. In contrast to a monatomic gas in which the order of magnitude of the dynamical pressure is O(1/c2), the dynamical pressure in a polyatomic gas is not small due to the internal motion of molecules as is the case in the classical limit. Therefore the present theory might result particularly useful in cosmology to describe some aspects of the post-recombination era.