We investigate the impact of radiation pressure on the circumbinary discs surrounding accreting massive black hole binaries (MBHBs) at milli-parsec separations using 3D hyper-Lagrangian resolution hydrodynamic simulations. The circumbinary discs in our simulations evolve under an adiabatic equation of state. The gas temperature was therefore allowed to change through viscous heating, black-body cooling, and self-gravity. We made a significant decision to also include the contribution of radiation pressure in the simulations. We modelled binaries with a total mass of 10⁶, M_⊙, eccentricities of e=0, 0. 45, 0. 9, and mass ratios of q= 0. 7, 1. We find that the radiation pressure significantly alters the vertical and thermal structure of the disc, resulting in a geometrically thinner and therefore colder configuration. This leads to a reduced accretion rate onto the binary and suppresses cavity eccentricity growth and precession in circular equal mass binaries. The binary eccentricity remains approximately constant, while the semi-major axis decreases over time due to net negative torque regardless of the initial binary orbital parameters.
Cocchiararo et al. (Tue,) studied this question.