A significant fraction of stars are members of gravitationally bound hierarchies containing three or more components. Almost all low-mass stars in binaries with periods shorter than three days are part of a hierarchical system. We therefore anticipate that a large fraction of compact galactic binaries detected by the Laser Interferometer Space Antenna will be members of hierarchical triple or quadruple system. The acceleration imparted by the hierarchical companions can be detected in the gravitational wave signal for outer periods as large as 100 years. For systems with periods that are shorter than, or comparable to, the mission lifetime, it will be possible to measure the period and eccentricity of the outer orbit. Laser Interferometer Space Antenna observations of hierarchical stellar systems will provide insight into stellar evolution, including the role that Lidov-Kozai oscillations play in driving systems toward merger.

• Received 1 June 2018
• Revised 15 August 2018

DOI:https://doi.org/10.1103/PhysRevD.98.064012