POSYDON: A General-purpose Population Synthesis Code with Detailed Binary-evolution Simulations

Abstract

Most massive stars are members of a binary or a higher-order stellar system, where the presence of a binary companion can decisively alter their evolution via binary interactions. Interacting binaries are also important astrophysical laboratories for the study of compact objects. Binary population synthesis studies have been used extensively over the last two decades to interpret observations of compact-object binaries and to decipher the physical processes that lead to their formation. Here, we present POSYDON, a novel, publicly available, binary population synthesis code that incorporates full stellar structure and binary-evolution modeling, using the MESA code, throughout the whole evolution of the binaries. The use of POSYDON enables the self-consistent treatment of physical processes in stellar and binary evolution, including: realistic mass-transfer calculations and assessment of stability, internal angular-momentum transport and tides, stellar core sizes, mass-transfer rates, and orbital periods. This paper describes the detailed methodology and implementation of POSYDON, including the assumed physics of stellar and binary evolution, the extensive grids of detailed single- and binary-star models, the postprocessing, classification, and interpolation methods we developed for use with the grids, and the treatment of evolutionary phases that are not based on precalculated grids. The first version of POSYDON targets binaries with massive primary stars (potential progenitors of neutron stars or black holes) at solar metallicity.

X-ray luminosity function of high-mass X-ray binaries: Studying the signatures of different physical processes using detailed binary evolution calculations

“…For our study, we used the POpulation SYnthesis with Detailed binary-evolution simulatiONs code (POSYDON; see Fragos et al 2023, for a detailed description of the code), a new binary population simulation framework that combines the flexibility of parametric binary population synthesis codes with detailed stellar structure and binary evolution models. Crucial to our study, POSYDON enables a physically accurate and self-consistent determination of the stability and mass-transfer rate evolution of mass-transfer phases thanks to extensive precomputed grids of binary-star models (using the Modules for Experiments in Stellar Astrophysics code or MESA code; Paxton et al 2011Paxton et al , 2013Paxton et al , 2015Paxton et al , 2018Paxton et al , 2019.…”

“…We assumed independent distributions of the mass ratio and period; however, recent studies show that there might be a dependence of mass ratios on the orbital periods (Moe & Di Stefano 2017). The initial orbital period is drawn from a power law in log-space (Sana et al 2013) with the same limits as the POSYDON grids (Fragos et al 2023) and the initial orbits are taken as circular since the current POSYDON version only follows the mass-transfer phases for circular binaries. The binary fraction assumed is 0.7 (Sana et al 2012).…”

“…Following the Fryer et al (2012) mechanism, f fb = 1.0 for stellar core masses (of the pre-collapse star) greater than 11 M and for masses lower than 11.0 M , f fb < 1.0. Hence, whenever f fb = 1.0, there is no baryonic mass loss considered, while still accounting for neutrino losses (which is capped at 0.5 M Fragos et al 2023). For NSs, when the SN mechanism follows the prescription from Fryer et al (2012), the fall-back fraction for NSs is f fb < 1.0 (however, for NSs from electron-capture SN, f fb = 0).…”

“…For NSs, when the SN mechanism follows the prescription from Fryer et al (2012), the fall-back fraction for NSs is f fb < 1.0 (however, for NSs from electron-capture SN, f fb = 0). When the SN mechanism follows the prescription from Patton & Sukhbold (2020), it is assumed that there is no fallback on the NS ( f fb = 0.0; Fragos et al 2023). (iii) The natal kicks are not normalized for BHs ( f fb = 0, therefore, n = 1).…”

The Missing Link between Black Holes in High-mass X-Ray Binaries and Gravitational-wave Sources: Observational Selection Effects

“…Therefore, they are known to have systematic effects on their produced binary populations (e.g., Shao & Li 2019;Gallegos-Garcia et al 2021;Marchant et al 2021). Most of the shortcomings associated with these approximations can be well addressed with state-of-the-art population synthesis codes like POSYDON (Fragos et al 2023), which use detailed MESA simulations (Paxton et al 2011) to model the full evolution of binary systems. Currently, such codes only cover a limited range of metallicities, and so cannot yet be used for studies such as ours.…”