The Formation of Black Holes in Non-interacting, Isolated Binaries. Gaia Black Holes as Calibrators of Stellar Winds From Massive Stars (2410.18501v1)

Abstract: Context. The black holes discovered using Gaia, especially Gaia BH1 and BH2, have low mass companions of solar-like metallicity in wide orbits. For standard isolated binary evolution formation channels including interactions such an extreme mass ratio is unexpected; especially in orbits of hundreds to thousands of days. Aims. Here, we investigate a non-interacting formation path for isolated binaries to explain the formation of Gaia BH1 and BH2. Methods. We use single star models computed with MESA to constrain the main characteristics of possible progenitors of long-period black hole binaries like Gaia BH1 and BH2. Then, we incorporate these model grids into the binary population synthesis code POSYDON, to explore whether the formation of the observed binaries at solar metallicity is indeed possible. Results. We find that winds of massive stars ($\gtrsim 80\,M_\odot$), especially during the Wolf-Rayet phase, tend to cause a plateau in the initial stellar mass to final black hole mass relation (at about $13\,M_\odot$ in our default wind prescription). However, stellar winds at earlier evolutionary phases are also important at high metallicity, as they prevent the most massive stars from expanding ($<100\,R_\odot$) and filling their Roche lobe. Consequently, the strength of the applied winds affects the range of the final black hole masses in non-interacting binaries, making it possible to form systems similar to Gaia BH1 and BH2. Conclusions. We deduce that wide binaries with a black hole and a low mass companion can form at high metallicity without binary interactions. There could be hundreds of such systems in the Milky Way. The mass of the black hole in binaries evolved through the non-interacting channel can potentially provide insights into the wind strength during the progenitors evolution.

• The paper models the formation of black holes in non-interacting binary systems using MESA and POSYDON simulations to investigate Gaia BH-like discoveries.
• The study highlights that strong stellar winds in massive stars, especially during the Wolf-Rayet phase, are crucial for limiting final BH mass and enabling non-interacting wide binary formation.
• The findings suggest that potentially hundreds of non-interacting black hole binaries, similar to Gaia BH1 and BH2, could exist in the Milky Way, detectable by astrometric missions like Gaia.

The Formation of Black Holes in Non-interacting, Isolated Binaries

This paper provides an in-depth analysis of a non-interacting formation path for isolated binary systems, focusing specifically on the formation of black holes (BHs) in such environments. Motivated by the discoveries of black holes with solar-like metallicity companions in wide orbits by the Gaia mission—particularly Gaia BH1 and BH2—this paper investigates whether these BHs could form without any significant binary interactions, such as mass transfer or tidal influences.

Methodology Overview

The researchers utilize the Modules for Experiments in Stellar Astrophysics (MESA) software to simulate single stellar evolution and POSYDON for binary population synthesis modeling. The combination allows a detailed exploration of the initial conditions and evolutionary paths that could lead to the formation of Gaia BH-like binaries. By employing varying wind-loss rates and mass-loss prescriptions at different evolutionary phases, they model the evolution of massive progenitors that can transform into BHs without significant interactions.

Key Findings

1. Wind Impact on Progenitor Evolution: The paper highlights the critical role of stellar winds in massive star evolution, particularly in stars exceeding 80 solar masses. The Wolf-Rayet (WR) phase winds contribute significantly to a plateau in the star's final mass before collapse into a black hole. This plateau forms the primary feature that aligns the calculated BH masses with observed values.
2. Mass Range and Metallicity Correlation: The results imply a metallicity-dependent mass-loss mechanism, leading to a typical BH mass around 13 solar masses in the explored models. Strong stellar winds at high metallicity prevent massive star-envelope expansion, thereby limiting Roche lobe filling and interaction within binary systems, enabling the formation of non-interacting wide-orbit binaries.
3. Predicted Population in the Milky Way: The findings suggest that numerous non-interacting BH binaries, similar to Gaia BH1 and BH2, could exist within the Milky Way, potentially numbering in the hundreds.

Implications and Future Directions

The paper’s conclusions stress the importance of stellar wind mass-loss prescriptions in shaping the end stages of massive stellar evolution and consequently affecting BH population statistics. The formation channels highlighted could recalibrate how astrophysicists perceive isolated stellar BH binaries, shifting emphasis onto wind-dominated evolution scenarios over binary interaction paths.

The results provoke several intriguing questions for future research. The sensitivity of BH mass distributions to stellar wind prescriptions offers a potential avenue for refining models of supernova progenitors. Further observational efforts to detect more systems like Gaia BH1/BH2 can provide valuable constraints on stellar evolution and BH formation theories.

Also, the potential existence of a large number of non-accreting BHs in wide binaries challenges traditional detection methods relying on X-ray emissions and suggests a promising application of astrometric missions like Gaia in expanding our catalog of stellar-mass black holes.

In conclusion, this analysis provides a compelling argument for the reconsideration of the traditional binary interaction-centric formation narratives and opens the door to refined evolution models that embrace stellar wind impacts, metal-dependent mass loss, and the formation of seemingly anomalous wide binaries in the galactic neighborhood.