Search for the isotropic stochastic background using data from Advanced LIGO's second observing run

Understand

The stochastic gravitational-wave background is a superposition of sources that are either too weak or too numerous to detect individually.

• In this study we present the results from a cross-correlation analysis on data from Advanced LIGO's second observing run (O2), which we combine with the results of the first observing run (O1).
• We do not find evidence for a stochastic background, so we place upper limits on the normalized energy density in gravitational waves at the 95% credible level of $\Omega_{\rm GW}<6.0\times 10^{-8}$ for a frequency-independent (flat) background and $\Omega_{\rm GW}<4.8\times 10^{-8}$ at 25 Hz for a background of compact binary coalescences.
• The upper limit improves over the O1 result by a factor of 2.8.