The optimal search for an astrophysical gravitational-wave background (1712.00688v2)

Abstract: Roughly every 2-10 minutes, a pair of stellar mass black holes merge somewhere in the Universe. A small fraction of these mergers are detected as individually resolvable gravitational-wave events by advanced detectors such as LIGO and Virgo. The rest contribute to a stochastic background. We derive the statistically optimal search strategy for a background of unresolved binaries. Our method applies Bayesian parameter estimation to all available data. Using Monte Carlo simulations, we demonstrate that the search is both "safe" and effective: it is not fooled by instrumental artefacts such as glitches, and it recovers simulated stochastic signals without bias. Given realistic assumptions, we estimate that the search can detect the binary black hole background with about one day of design sensitivity data versus $\approx 40$ months using the traditional cross-correlation search. This framework independently constrains the merger rate and black hole mass distribution, breaking a degeneracy present in the cross-correlation approach. The search provides a unified framework for population studies of compact binaries, which is cast in terms of hyper-parameter estimation. We discuss a number of extensions and generalizations including: application to other sources (such as binary neutron stars and continuous-wave sources), simultaneous estimation of a continuous Gaussian background, and applications to pulsar timing.

• The paper introduces a Bayesian parameter estimation method to optimally detect the gravitational-wave background from compact binary mergers.
• It employs Monte Carlo simulations to demonstrate robustness and unbiased recovery of weak signals amidst instrumental noise.
• The method significantly reduces detection time, estimating background detection within one day versus months for traditional searches.

The Optimal Search for an Astrophysical Gravitational-Wave Background

In the paper "The optimal search for an astrophysical gravitational-wave background," the authors, Rory Smith and Eric Thrane, introduce a statistically optimal method for detecting a stochastic gravitational-wave background from unresolved compact binary mergers. This approach significantly improves the sensitivity compared to traditional methods, such as the cross-correlation technique commonly used in LIGO and Virgo collaborations.

Key Contributions and Methodology

The primary focus of the research is on deriving a Bayesian-based search strategy that exploits the identifiable characteristics of the non-Gaussian nature of the gravitational-wave background from binary black holes. The adoption of a Bayesian framework allows the method to incorporate prior information effectively and produce minimum credible interval posteriors.

1. Bayesian Parameter Estimation: The authors implement a Bayesian parameter estimation approach applied to all available data. This approach ensures the background noise does not significantly impact the results and that the search remains unbiased by instrumental artifacts.
2. Monte Carlo Simulations: Through detailed Monte Carlo simulations, the authors demonstrate that the method is robust, recovering simulated stochastic signals without bias. The effectiveness and reliability are essential, given the challenges in detecting weak signals buried within instrumental noise.
3. Significant Reduction in Detection Time: The method showcases a substantial improvement over the traditional cross-correlation search, estimating detection of the binary black hole background within one day of data at design sensitivity, as opposed to approximately 40 months of observation time required by conventional searches.
4. Hyper-parameter Estimation Framework: The paper provides a comprehensive framework for examining the population properties of compact binaries. Notably, it breaks the degeneracy between merger rates and black hole mass distributions, allowing for independent constraints on these parameters.
5. Robust to Non-Gaussian Noise Artifacts: The technique's resilience to noise artifacts, such as glitches, is notably addressed, ensuring that the search results remain valid across real-world data settings.

Implications and Future Directions

The methodological advancements presented in this research have several implications for both current and future gravitational-wave astronomy endeavors:

• Acceleration of Scientific Discoveries: The significant reduction in necessary observation time increases the feasibility of practical detection of the stochastic background, accelerating scientific discoveries related to compact binary systems.
• Improved Population Modeling: The ability to constrain merger rates and masses with less observational data enhances theoretical modeling of black hole and neutron star populations, leading to more accurate astrophysical inferences and improved understanding of stellar evolution processes.
• Broad Applicability: While the paper primarily focuses on binary black holes, the outlined Bayesian framework is adaptable to other astrophysical sources, including binary neutron stars and possibly continuous-wave sources, representing a versatile tool for future research.
• Potential for Cross-Disciplinary Integration: The success of this method opens avenues for integrating gravitational-wave data with other observational modalities, such as electromagnetic counterparts of binary neutron star mergers, further enriching multi-messenger astronomy.

Looking forward, refinements in computational techniques and extensions to account for simultaneous measurement of Gaussian and non-Gaussian backgrounds are necessary for maximizing the potential of this approach. The prospects of detecting primordial gravitational-wave backgrounds, layered beneath astrophysical sources, pose intriguing challenges yet promise profound insights into the early Universe.

In conclusion, this paper provides a vital step towards enhancing the sensitivity and efficiency of gravitational-wave background searches, offering innovative solutions poised to have lasting impacts in the field of gravitational-wave cosmology.