Prospects for detecting gravitational waves at 5 Hz with ground-based detectors

TL;DR

The paper proposes an upgraded LIGO detector, LIGO-LF, optimized for 5-30 Hz sensitivity, which significantly enhances detection capabilities for black hole mergers, neutron star coalescences, and other astrophysical phenomena.

Contribution

This study introduces LIGO-LF, a feasible upgrade to aLIGO that improves low-frequency sensitivity and expands astrophysical detection potential using current and developing technologies.

Findings

LIGO-LF can detect stellar-mass black hole mergers up to z~6.

Detection rate of black hole mergers increases by a factor of 18.

Localization of neutron star mergers improves by a factor of 10.

Abstract

We propose an upgrade to Advanced LIGO (aLIGO), named LIGO-LF, that focuses on improving the sensitivity in the 5-30 Hz low-frequency band, and we explore the upgrade's astrophysical applications. We present a comprehensive study of the detector's technical noises and show that with technologies currently under development, such as interferometrically sensed seismometers and balanced-homodyne readout, LIGO-LF can reach the fundamental limits set by quantum and thermal noises down to 5 Hz. These technologies are also directly applicable to the future generation of detectors. We go on to consider this upgrade's implications for the astrophysical output of an aLIGO-like detector. A single LIGO-LF can detect mergers of stellar-mass black holes (BHs) out to a redshift of z~6 and would be sensitive to intermediate-mass black holes up to 2000 M_\odot. The detection rate of merging BHs will increase by a factor of 18 compared to aLIGO. Additionally, for a given source the chirp mass and total mass can be constrained 2 times better than aLIGO and the effective spin 3-5 times better than aLIGO. Furthermore, LIGO-LF enables the localization of coalescing binary neutron stars with an uncertainty solid angle 10 times smaller than that of aLIGO at 30 Hz, and 4 times smaller when the entire signal is used. LIGO-LF also significantly enhances the probability of detecting other astrophysical phenomena including the tidal excitation of neutron star r-modes and the gravitational memory effects.