Multiband Gravitational-Wave Astronomy: Detectors, Source Populations, and Precision Tests

Meenu Mohil, Vijay Rawat

Abstract: Albert Einstein first proposed the existence of gravitational waves in 1916 as a consequence of his general Theory of Relativity. For nearly a century, these waves remained purely theoretical until 2015, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors achieved the first direct detection of a binary black hole merger. This breakthrough marked the beginning of gravitational-wave astronomy, now supported by the KAGRA detector, forming the LIGO-Virgo-Kagra (LVK) collaboration. Since then, more than ninety compact binary coalescences have been confirmed. During the ongoing fourth observing run (O4, 2023-2025), over two hundred public alerts have already been issued, including 128 new confirmed candidates in the GWTC-4.0 catalogue. These results are made possible by improved detector sensitivity, reduced quantum noise, and advances in data analysis methods such as matched filtering, machine learning algorithms, convolutional neural networks, and normalizing flows. This review outlines the theoretical background, observational developments, and data analysis framework of gravitational-wave science in a way that supports both undergraduate and postgraduate teaching in relativity and astrophysics. It discusses how detectors- from ground-based interferometers like LIGO, Virgo and KAGRA, to pulsar timing arrays (such as NANOGrav and EPTA) and space missions like LISA-cover a wide frequency range, from nanohertz to kilohertz. The paper also traces the transition from isolated detection to large-scale population studies through the successive observing runs. The review includes a case study of orbital parameter estimation that provides examples to be used in classroom simulations using open-access data. The wider themes associated with these ideas include multi-messenger astronomy, cosmological distance measurements, and gravitational physics precision tests. Easy access to open data sources such as GWOSC gives instructors the opportunity to teach students about the waveform analysis and statistical inference processes in a very practical manner.

Keywords: Gravitational waves, general relativity, matched filtering, compact binary coalescences, multi-messenger astronomy

How to Cite?: Meenu Mohil, Vijay Rawat, "Multiband Gravitational-Wave Astronomy: Detectors, Source Populations, and Precision Tests", Volume 14 Issue 12, December 2025, International Journal of Science and Research (IJSR), Pages: 154-170, https://www.ijsr.net/getabstract.php?paperid=SR251201192533, DOI: https://dx.doi.org/10.21275/SR251201192533