Sensitivity of stellar physics to the equation of state

Abstract

The formation and evolution of stars depends on various physical aspects of stellar matter, including the equation of state (EOS) and transport properties. Although often dismissed as `ideal gas-like' and therefore simple, states occurring in stellar matter are dense plasmas, and the EOS has not been established precisely. EOS constructed using multi-physics approaches found necessary for laboratory studies of warm dense matter give significant variations in stellar regimes, and vary from the EOS commonly used in simulations of the formation and evolution of stars. We have investigated the sensitivity of such simulations to variations in the EOS, for sun-like and low-mass stars, and found a strong sensitivity of the lifetime of the Sun and of the lower luminosity limit for red dwarfs. We also found a significant sensitivity in the lower mass limit for red dwarfs. Simulations of this type are also used for other purposes in astrophysics, including the interpretation of absolute magnitude as mass, the conversion of inferred mass distribution to the initial mass function using predicted lifetimes, simulations of star formation from nebulae, simulations of galactic evolution, and the baryon census used to bound the exotic contribution to dark matter. Although many of the sensitivities of stellar physics to the EOS are large, some of the inferred astrophysical quantities are also constrained by independent measurements, although the constraints may be indirect and non-trivial. However, it may be possible to use such measurements to constrain the EOS more than presently possible by established plasma theory.