Research Projects

The project aims to probe one of the open questions in the field of astrophysics and cosmology related to the formation and evolution of black holes in the Universe. Observations from electromagnetic observations have given the existence of black holes with a few times the mass of the sun to a few tens of million times the mass of the sun. But how these black holes come into existence with cosmic time and evolve into these heavy black holes remains unknown. Moreover, the interplay between the evolution of black holes with the evolution of stars and galaxies in the Universe is yet to be discovered. Gravitational Waves brings a new window to directly study the black holes in the Universe up to large cosmological distance making it a powerful probe to explore the physics of formation and evolution of the black holes over cosmic time and bring new insights to these open questions. Gravitational Waves from binary black holes can be measured from nano-hertz to kilo-hertz frequencies depending on their masses. The heavier black holes are detectable at the low-frequency GW signal, whereas the lighter mass black holes are detectable at high frequency. As a result, by using multi-band GW signal from nano-hertz to kilo-hertz one can make a data-driven inference of black hole properties in the Universe and shed light for the first time on the hierarchy of black hole formation across its masses and cosmic time. We propose to build a state-of-the-art technique that will use GW events detected from LIGO-Virgo-KAGRA and GW stochastic background from nano-hertz to make a data-driven inference of the black hole mass distribution with cosmic redshift over the mass range from a few solar mass to supermassive black hole. The LVK GW signal can shed light on the mass distribution of stellar mass black holes and its dependence on the cosmic redshift. Our analysis will provide a measurement of delay time distribution and can shed light on different scenarios of formations from observations that are in synergy with the cosmic evolution of star formation rate and stellar metallicity. Also, the low-frequency stochastic GW signal will be able to shed light on the merger rate of supermassive black holes using the all-sky stochastic GW background spectral shape. The combination of these multi-band GW signals will be the first of its kind which will give insight into the black hole formation and evolution history and will enable a deeper understanding of the hierarchy of black hole evolution in the Universe. The tools that will be developed in this project will be published in international journals and will be available for the use of future GW data analysis feasible from the hecto-hertz range with LVK and LIGO-India and in the nano-hertz range with Square Kilometer array, in both of which India is a member. The PI is a member of LIGO, LIGO-India, and NANOGrav collaboration and will be able to implement the techniques for future analysis as well.