Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo (1811.12940v4)

Abstract: We present results on the mass, spin, and redshift distributions with phenomenological population models using the ten binary black hole mergers detected in the first and second observing runs completed by Advanced LIGO and Advanced Virgo. We constrain properties of the binary black hole (BBH) mass spectrum using models with a range of parameterizations of the BBH mass and spin distributions. We find that the mass distribution of the more massive black hole in such binaries is well approximated by models with no more than 1% of black holes more massive than $45\,M_\odot$, and a power law index of $\alpha = {1.3}^{+1.4}_{-1.7}$ (90% credibility). We also show that BBHs are unlikely to be composed of black holes with large spins aligned to the orbital angular momentum. Modelling the evolution of the BBH merger rate with redshift, we show that it is at or increasing with redshift with 93% probability. Marginalizing over uncertainties in the BBH population, we find robust estimates of the BBH merger rate density of $R = {53.2}^{+55.8}_{-28.2}$ Gpc$^{-3}$ yr$^{-1}$ (90% credibility). As the BBH catalog grows in future observing runs, we expect that uncertainties in the population model parameters will shrink, potentially providing insights into the formation of black holes via supernovae, binary interactions of massive stars, stellar cluster dynamics, and the formation history of black holes across cosmic time.

• The paper infers binary black hole mass spectra, showing a power-law decline beyond about 45 solar masses linked to pair-instability limits.
• The study employs population models to reveal a preference for nearly equal mass ratios and consistently low spin magnitudes.
• It examines merger rate evolution with redshift, indicating a mild increase while underscoring the need for larger observational datasets.

Analyzing Binary Black Hole Populations Using LIGO and Virgo Observations

This paper presents an analysis of binary black hole (BBH) merger events detected during the first and second observing runs of the Advanced LIGO and Advanced Virgo facilities. The primary focus of this research is to infer the properties of the BBH mass spectrum and spin distributions and to explore the evolution of the merger rate density with redshift. The analysis utilizes the results from ten BBH mergers detected by the observatories. The paper employs phenomenological population models to constrain the mass, spin, and redshift distributions, offering insights into the astrophysical formation channels of BBHs.

The paper introduces three mass distribution models, each with increasing complexity, which consider power-law and Gaussian components. The paper finds that the mass distribution is primarily described by a power-law with a cutoff, indicating a significant reduction in merger rates for primary masses greater than approximately 45 solar masses. This aligns with theoretical predictions involving pair-instability supernovae that suggest limits on black hole masses formed from stellar origins. Additionally, the models show preferences for BBH systems with comparable mass ratios, suggesting that the mass-ratio distribution is nearly flat or declining sharply for more asymmetric binaries.

The analysis also examines black hole spin distributions, considering spin magnitude and orientation. The paper highlights a preference for distributions with low spin magnitudes, showing that most BH spins are consistent with low or even zero values. The results argue against scenarios involving second-generation mergers, where components are expected to have higher spins. Despite extensive modeling efforts, the paper notes limitations in current data to effectively constrain spin orientations, illustrating challenges in distinguishing between isotropic and aligned spin models.

Furthermore, the paper investigates the merger rate density's evolution with redshift, comparing models with varying degrees of redshift dependence. The results suggest a mild preference for an increasing merger rate with redshift, although no strong conclusion is drawn due to the limited sample size. The findings underscore the importance of more expansive observational data for refining these models and improving constraints.

The paper acknowledges the systematic uncertainties inherent in the paper, such as waveform model selection and detection efficiency estimation. However, these are found to be secondary to statistical uncertainties arising from the small sample size. Future improvements in observational capabilities and theoretical model development are anticipated to mitigate these issues and enable more granular insights into BBH formation channels.

The observed upper limit on the BBH mass spectrum, preference for nearly equal mass-ratio binaries, and inclination towards low spin magnitudes align with theoretical predictions and provide crucial constraints for astrophysical models. This research paves the way for future work, which will greatly benefit from increased event detections in subsequent LIGO/Virgo observing runs, enabling more precise differentiation between competing astrophysical scenarios. As the catalog of BBH mergers expands, these analyses will deepen the understanding of BBH formation and evolution, contributing significantly to the field of gravitational-wave astronomy.