Research

Research interest

  • Galactic dynamics
  1. Self-gravitating response theory for perturbed collisionless systems like galaxies and cold dark matter halos (linear and non-linear regimes), relaxation of collisionless systems (phase-mixing, Landau damping, violent relaxation, chaotic mixing, etc.)
  2. Role of resonances and chaos in the secular evolution of galaxies and star-clusters via dynamical friction, dynamical buoyancy and core-stalling
  3. Secular processes like radial migration and angular momentum transport driven by bars and spiral arms
  4. Gravitational encounters and mergers between star clusters, galaxies, dark matter halos, etc. and the associated phenomena of mass loss, tidal shocks, revirialization, tidal disruption and so on
  • Dark matter
  1. Constraining the nature of dark matter using galactic dynamics, e.g., dynamical friction on satellite galaxies and star clusters in cored vs cuspy host galaxies, diffusion of dynamically cold stellar streams by dark matter substructure, etc.
  2. Impact of alternative dark matter models (Ultralight axion or fuzzy dark matter, Self-interacting dark matter, QCD axion, etc.) on structure-formation, secular evolution of galaxies, etc.
  • Black holes
  1. Black hole mergers: dynamical friction, loss-cone dynamics, gravitational waves
  2. Strong gravitational lensing due to black holes
  • Cosmology
  1. Inflation, cosmological phase-transitions, primordial black holes
  2. Non-linear growth of perturbations and structure formation
 

PhD Research

As part of my PhD research with Prof. Frank van den Bosch at Yale, I have worked on the dynamics of self-gravitating, collisionless systems such as galaxies, star-clusters and cold dark matter halos. I have developed both perturbative as well as non-perturbative theories for the response of collisionless systems to gravitational perturbations/encounters. I developed a general non-perturbative formalism to compute the energy transfer and mass-loss in penetrating, impulsive encounters between galaxies or dark matter halos, which I validated using N-body simulations. A proper treatment of near-resonant encounters, e.g., the dynamical friction driven in-fall of massive perturbers orbiting in spherical host systems, required more sophisticated analytical techniques. I generalized the standard LBK formalism and came up with a self-consistent perturbative formalism to compute the dynamical friction torque exerted on a perturber in a circular orbit. This proved to be a huge improvement over the standard theory since my self-consistent formalism presented a resolution (within the perturbative framework) to the outstanding problems of core-stalling, the cessation of dynamical friction driven in-fall of a perturber in the core region of a host system with cored density profile, and dynamical buoyancy, an enhancing torque counteracting dynamical friction and pushing the perturber outwards from deep inside the core. To capture the non-linear effects of core dynamics, I also developed a non-perturbative orbit-based formalism in the restricted three body framework that shed light on the near-resonant orbits of field particles responsible for dynamical buoyancy and core-stalling. This elucidated that core-stalling arises from a bifurcation of the Lagrange points (fixed points in the co-rotating frame) at a certain critical radius in the core, on either side of which the orbital configuration is drastically different, culminating in friction outside and buoyancy inside the critical bifurcation radius. These dynamical phenomena present a promising avenue to constrain the nature of dark matter by looking for offsets of supermassive black holes and nuclear star clusters from the centers of dark matter dominated dwarf galaxies, the presence (absence) of which would favour a cored (cuspy) dark matter density profile.
 
I am currently working on developing a response theory for perturbed disk galaxies to describe their post-perturbation relaxation through kinematic processes like phase-mixing and collective processes like Landau damping. This work is dedicated towards doing Galactoseismology, i.e., understanding the origin of the phase-space spirals observed by Gaia in the Solar neighborhood (what kind of perturbations caused them) and ultimately using them to constrain the potential and thus the dark matter distribution of the Milky Way.