Assessing the potential of LIGO-India in resolving the Hubble Tension

TL;DR

LIGO-India's addition to the gravitational wave network significantly enhances the detection and localization of neutron star mergers, potentially reducing the time needed to measure the Hubble constant and addressing the Hubble Tension.

Contribution

This paper demonstrates through simulations that LIGO-India can greatly improve detection rates and localization, accelerating the use of gravitational wave observations to measure H0.

Findings

LIGO-India could increase BNS event detections by 2-7 times.

Improved localization enables deeper EM follow-up, increasing detection of EM counterparts by ~20.

LIGO-India can reduce the H0 measurement time from decades to a few years.

Abstract

Determining the Hubble constant (H0), a fundamental parameter describing cosmic expansion, remains a challenge due to conflicting measurements from the early and late universe. Gravitational wave (GW) observations from binary neutron star (BNS) mergers, with identified host galaxies through electromagnetic (EM) follow-up, offer an independent method to measure H0. However, this requires detection of numerous events, which could take decades with current GW detectors. LIGO-India can dramatically accelerate this effort. With sensitivity comparable to the existing LIGO detectors, its addition to the LIGO-Virgo network could increase detected events by 70%. This improvement nearly doubles when accounting for the detector's 70% duty cycle, increasing the probability of simultaneous operation of three detectors by a factor of ~2. We perform end-to-end simulations to estimate triple-coincidence detection rates and sky localization, considering realistic BNS populations, lightcurves, and EM observatory specifications. Our findings suggest LIGO-India could increase BNS events with observed kilonovae by ~2-7 times. The factor of few improvements in source localization precision with LIGO-India can allow much deeper EM follow-up campaigns (not considered in the simulations), potentially increasing the overall rate of detection of EM counterparts by a factor of ~20, which can have an enormous impact in addressing critical questions in different areas of astronomy. We evaluate the impact of LIGO-India in the context of H0 measurement and argue that it can cut down the required observation time of several decades by a factor of few and possibly to just few years with regular sensitivity upgrades.