Research Interests

1. Black Hole Information Paradox

Stephen Hawking, in the 1970s, tried to calculate quantum mechanical effects at the event horizon of a black hole. He found that a black hole constantly emits photons (Hawking Radiation) and is expected to do this throughout its entire life until it evaporates completely. The energy of these photons depends only on the mass of a black hole. An older version of the paradox can be understood by taking an example of a library which collapses to form a black hole which eventually evaporates due to this Hawking Radiation. If we recollect all these emitted photons, the only property that we can deduce about the black hole is its mass. This black hole of the given mass could have been formed from the collapse of many different kinds of objects, and thus we cannot retrieve the library back from the black hole. This process is in contradiction to a fundamental principle in physics, the principle of reversibility. The information about the collapse of the library appears to be lost as the black hole evaporates. This problem is considered one of the most fundamental problems in unifying quantum mechanics and general relativity.

2. Dark Energy Models

In 1930s Edwin Hubble showed that our universe is expanding. Till 1998 it was widely believed that this expansion of the universe would be eventually slowed down. This slowing down was attributed to the fact that the universe is full of matter and the attractive force of gravity pulls all matter together. But the Hubble Space Telescope (HST) observations of very distant supernovae in 1998 showed that the universe was expanding more slowly earlier in time than it is today. And contrary to the popular belief the expansion of the universe is in fact accelerating. One of the explanations theorists have come up with is there is some strange kind of energy-fluid named as “Dark Energy” that fills the entire space. Dark Energy contributes around 70% to the total energy budget of the universe, still very less is known about its nature. I am currently working on a project which involves studying the properties of various Dark Energy Models to understand the physical nature of Dark Energy. The details can be found here

3. 21-cm Cosmology

With the advent of several ground based and space based telescopes, we have been able to directly observe the galaxies out to distances corresponding to a time when the Universe was a billion years old. The detection of CMB in 1964 allowed us to probe the primordial universe when it was just 400,000 years old. However when it comes to the observation of the era connecting the two aforementioned periods, the picture still remains blurry. This middle era is possibly one of the most interesting epochs in the evolution of the universe when the first stars and galaxies came into existence. 21-cm Cosmology is an alternative attempt to indirectly observe the first stars and galaxies using the 21-cm signal emitted by the abundant neutral-H in the early universe. With the development of several recent attempts like James Webb Space Telescope(JWST) to observe the universe at very high redshifts, the field of 21-cm Cosmology becomes an exciting area where we’ll get to test our theoretical predictions against the observations and study the birth of first stars and galaxies. Here you can find the details of a project in this direction on which I’m currently working.

4. Gravitational Waves

In his General Theory of Relativity, Albert Einstein predicted the existence of Gravitational Waves(GWs) in 1916. GWs can be better understood by considering the analogy with Electromagnetic Waves. Just like an accelerating charge radiates EM waves, an accelerating (and anisotropic) mass emits energy in Gravitational Waves. The strongest GWs are produced by some of the most violent events in the universe, like Black Hole (or Neutron Star) Collisions or Supernovae Explosions. Apart from these Astrophysical sources, GWs can also be of cosmological origin, which were emitted at the end of inflation. These GWs are called Primordial GWs. I am primarily interested in studying the properties of GWs from various astrophysical sources and Primordial GWs. Here you can find the details of a project I completed as part of the Gravitational Waves Astronomy course offered in the Autumn 2022 sem.

5. CMB Anisotropies and Polarisation

Until 3,40,000 years after the Big Bang, our universe was in an ionised state and all the photons from that era got scattered off due to a large number of free electrons. As the universe expanded and the temperature dropped, the free electrons and protons combined to form neutral atoms. This allowed photons to stream freely through space as the number of free electrons dropped. These photons that propagate through the universe and reach us are referred to as the Cosmic Microwave Background (CMB). The temperature of this radiation is roughly uniform (~2.7K) across all directions with small anisotropies of the order 1 in $10^5$. These anisotropies are crucial in understanding many puzzling problems about the early universe. The CMB also carry two modes of polarisations - E and B. I am particularly interested in studying the B mode as it contains signatures of the primordial gravitational waves, which are very difficult to detect otherwise.

6. Galaxies

Though a galaxy is a fairly complex system containing millions of stars, still we can study them as one entity and deduce certain important properties about its constituents. My primary interests in this area involve the study of high redshift galaxies and galaxy evolution. I am currently working on a project which involve the study of photometric properties of high redshift galaxies using James Webb Space Telescope (JWST) data.