Abstract
The recent Advanced LIGO detection of gravitational waves from the binary black hole GW150914 suggests there exists a large population of merging binary black holes in the Universe. Although most are too distant to be individually resolved by advanced detectors, the superposition of gravitational waves from many unresolvable binaries is expected to create an astrophysical stochastic background. Recent results from the LIGO and Virgo Collaborations show that this astrophysical background is within reach of Advanced LIGO. In principle, the binary black hole background encodes interesting astrophysical properties, such as the mass distribution and redshift distribution of distant binaries. However, we show that this information will be difficult to extract with the current configuration of advanced detectors (and using current data analysis tools). Additionally, the binary black hole background also constitutes a foreground that limits the ability of advanced detectors to observe other interesting stochastic background signals, for example, from cosmic strings or phase transitions in the early Universe. We quantify this effect.
- Received 8 April 2016
DOI:https://doi.org/10.1103/PhysRevX.6.031018
This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The detection of gravitational waves from the binary black hole merger GW150914 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) initiated the era of gravitational-wave astronomy. For every “loud” event such as GW150914 observed by advanced detectors, there are likely to be many more events that are too distant and therefore too “quiet” to resolve. Although such events cannot be individually detected, the superposition of gravitational waves from these unresolved binaries creates a stochastic background, which is likely detectable by advanced detectors operating at design sensitivity. Here, we investigate what measurements of the stochastic background can teach us about distant binaries and how this information complements the observation of more nearby individual binaries.
First, we demonstrate that the stochastic gravitational-wave background is dominated by high-redshift (i.e., distant; ) sources and therefore probes an astrophysically distinct population from resolvable binaries. Second, we demonstrate that the most interesting spectral features of the stochastic background (which encode, for example, the black hole mass and redshift distributions) are unlikely to be measured by advanced detectors. Third, we show that the stochastic background from black hole mergers is likely to obscure any underlying cosmological gravitational-wave background.
While our results highlight the limitations of existing detector networks and data analysis strategies, future developments may better reveal information currently hidden in the stochastic background. We anticipate that it may be possible to gain new insights through the development of searches for a non-Gaussian background and/or through improvements to detector network sensitivity at high frequencies.