Research
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Gravitational waves are “ripples” in spacetime, generated by accelerated mass. They are a direct result of Einstein’s general theory of relativity. After 100 years since Einstein published his theory, in 2015, LIGO made the first-ever direct detection of gravitational waves from a binary black hole merger. This has opened up a whole new window for us to observe the universe. In 2017, LIGO and Virgo observed gravitational waves from a binary neutron star merger which was subsequently seen in electromagnetic observations. This has further led to the focus on multi-messenger astronomy. With further improvements in the current ground based observatories and future space based observatories like LISA on the horizon, there is a focus now on building up tools and studies to prepare for detecting new sources for the next generation of gravitational wave detectors.
Waveform Modelling
For LIGO to detect the gravitational wave signals, we need prior information about the signal in order to search for it in the noisy data. Thus it is important to model the gravitational waveforms for binary black hole mergers throughout its three main stages - inspiral, merger and ringdown. We solve Einstein’s equation numerically or use analytical methods like a post-Newtonian expansion to model source waveforms. Gravitational waveform modelling ranges in its formalism and models characteristics of the source (Spin, eccentricity, mass ratio etc..).
I’m involved in modelling GWs from binary black holes in eccentric orbits. The emission of gravitational waves will reduce the eccentricity of the binary orbit. By the time the wave enters the sensitivity of the LIGO band, the orbit will circularise. Hence the detections so far have been from binaries that are nearly circular, but we expect to measure orbital eccentricity with future gravitational wave detectors. Therefore we need to build eccentric waveform models that are analytic and can be used in the future for parameter estimation. I work on developing a fully analytical inspiral frequency domain model that incorporates eccentricity and includes non-quadrupole modes. The inspiral model is used to construct a full IMR model in the frequency domain with the help of hybrid waveforms constructed from Numerical Relativity simulations.
I’m also looking into developing ENIGMA (Eccentric Non-Gaussian I ) waveform to expand its formalism to general orbit and quasi-keplerian formalism. This model is currently a non-spinning model, and we’d like to add spin effects to construct a GW model for spinning BBH finally. This model will be used in future LIGO searches.
Gravitational Wave Sources
We can infer many things from Gravitational Wave data, such as the characteristics of the source and its Astrophysics. With the advent of multi-messenger astronomy, we can now look at the same astronomical phenomena in different wavelengths and from gravitational wave data. I worked on sources for the upcoming LISA detector, called verification binary. These binaries are well-known from electromagnetic observations, are a guaranteed LISA source, and are crucial in the instrument’s initial functional tests. I developed a method to calculate the inclination and orientation angle of the binary using polarimetric methods.
Primordial Gravitational Waves
Primordial gravitational waves are relics from the early history of the universe right after the Big Bang. They are significant to study the inflationary phase of the universe. These waves still form a stochastic background, and it is possible to detect this faint signal from gravitational data, primarily from the Pulsar Timing Array experiment. I’m currently studying the evolution of these primordial tenor perturbations from inflation and the reheating phase of the universe and looking at how different inflation models could be verified based on the detection of the stochastic gravitational-wave background.