Radiating Bondi Flows I: Dimensionless Framework and Constant Opacity Solutions

Abstract

In this paper, we extend the foundational work of Bondi (1952) to include the effects of radiative feedback in gas-pressure-dominated environments. We construct steady-state spherically symmetric accretion solutions including radiative heating and cooling. Under the simplifying assumption of a constant opacity, the solutions are controlled by four dimensionless parameters: the adiabatic index $\gamma$, optical depth through the Bondi radius $\tau_B$, dimensionless luminosity at infinity $\tilde{L}_\infty$, and a characteristic dimensionless cooling time $\beta$. We present numerical solutions across the dimensionless parameter space $(\tau_B, \tilde{L}_\infty, \beta)\in [10^{-3}, 10^3]$. Contrary to radiation-pressure-dominated environments, radiative feedback primarily operates to suppress accretion -- particularly at high $\tau_B$, $\tilde{L}_\infty$, and/or $\beta$. We also present analytic descriptions confirming the suppressive nature of this feedback and give the scalings for the accretion rate $\dot{M}\sim \tilde{L}_\infty^{-5/4}$ at large $\tilde{L}_\infty$, $\dot{M}\sim \tau_B^{-10/11}\beta^{-5/11}$ at large $\tau_B$, and $\dot{M}\sim (\tilde{L}_\infty\tau_B)^{-5/8}$ for large $\tilde{L}_\infty\tau_B$. We discuss the potential role of convection in these steady-state solutions, and the particular relevance to problems of planet formation where radiative heating is significant, but the system remains in the gas-pressure-dominated regime.