GW150914: Implications for the stochastic gravitational wave background from binary black holes (1602.03847v2)

Abstract: The LIGO detection of the gravitational wave transient GW150914, from the inspiral and merger of two black holes with masses $\gtrsim 30\, \text{M}\odot$, suggests a population of binary black holes with relatively high mass. This observation implies that the stochastic gravitational-wave background from binary black holes, created from the incoherent superposition of all the merging binaries in the Universe, could be higher than previously expected. Using the properties of GW150914, we estimate the energy density of such a background from binary black holes. In the most sensitive part of the Advanced LIGO/Virgo band for stochastic backgrounds (near 25 Hz), we predict $\Omega\text{GW}(f=25 Hz) = 1.1_{-0.9}^{+2.7} \times 10^{-9}$ with 90\% confidence. This prediction is robustly demonstrated for a variety of formation scenarios with different parameters. The differences between models are small compared to the statistical uncertainty arising from the currently poorly constrained local coalescence rate. We conclude that this background is potentially measurable by the Advanced LIGO/Virgo detectors operating at their projected final sensitivity.

• The paper presents that GW150914’s high-mass merger significantly boosts the predicted energy density of the stochastic gravitational-wave background from binary black holes.
• It employs diverse binary formation scenarios and merger rate calculations to estimate the dimensionless energy spectrum, ΩGW, with refined accuracy.
• The findings refine detection strategies by linking astrophysical models with advanced gravitational-wave detector sensitivities.

Implications of GW150914 for the Stochastic Gravitational-Wave Background from Binary Black Holes

The detection of the gravitational wave event GW150914 by the LIGO and Virgo collaborations marked a significant milestone in the field of astronomy and astrophysics, specifically in the paper of gravitational waves. This event, attributed to the inspiral and merger of two black holes with masses around 30 solar masses, has implications that extend beyond the individual observation, providing insights into the stochastic gravitational-wave background generated by binary black holes across the universe.

Overview of Findings

The paper under discussion presents an investigation into the implications of GW150914 for the stochastic gravitational-wave background from binary black holes. The stochastic background is generated by the superposition of gravitational waves from numerous unresolved binary systems, which form a continuous background signal detectable through correlation analyses of multiple detectors.

The paper predicts that due to the relatively high masses of the black holes involved in GW150914, the energy density of the stochastic background, denoted by $\Omega_{\text{GW}}(f)$, may be higher than anticipated in prior models. At a frequency of 25 Hz, which is within the most sensitive part of the LIGO/Virgo detection band for stochastic backgrounds, the predicted value of $\Omega_\text{GW}$ is 1.1 with a significant range due to the uncertainties in coalescence rates and mass distributions.

Methodology

The authors employ a variety of formation scenarios to robustly demonstrate their predictions under different assumptions. The stochastic background is characterized using a dimensionless energy density spectrum, which is sensitive to the merger rates of black holes, their masses, spins, and the redshift evolution of these systems across cosmic time. These factors are combined to calculate the cumulative energy spectrum of such events, predicting an observable stochastic background within the operational sensitivity of the Advanced LIGO and Virgo detectors.

Implications

The findings suggest that GW150914-like events contribute significantly to the overall stochastic background, potentially making it measurable with current gravitational-wave detectors. This has profound implications for:

1. Astrophysical Insights: Understanding the population of binary black holes, their formation environments, and the evolution of such systems.
2. Model Refinement: Providing constraints and refinement for models of stellar evolution, binary interaction physics, and population synthesis models.
3. Detection Strategies: Informing the development of detection strategies for stochastic backgrounds, emphasizing the role of detector networks and data analysis techniques to isolate such signals amidst noise.

Future Directions

This research paves the way for future observations and analyses of the gravitational-wave stochastic background. The implications for upcoming gravitational-wave observatories, both upgrades in current facilities and new concepts such as the Einstein Telescope or space-based detectors like LISA, are considerable. These platforms will refine measures of $\Omega_\text{GW}$, offering enhanced sensitivity to detect and characterize the stochastic gravitational-wave background.

In conclusion, the detection of GW150914 has direct implications for understanding a broader background of gravitational waves, encouraging continuous exploration of both resolved and unresolved gravitational signals from cosmic events. These efforts contribute to a deeper understanding of the universe's dynamic structure, governed by the fundamental phenomenon of gravity.