Gravitational waves · compact objects · relativistic fluids
Abhishek Hegade K. R.
I am an Associate Research Scholar at the Princeton Gravity Initiative, where I study the dynamics of strongly gravitating systems. My current research focuses on the tidal dynamics of neutron stars, extreme mass-ratio inspirals in accretion disks, and the effects of weakly collisional plasma physics on accretion flows around supermassive black holes. Before joining Princeton, I completed my PhD at the University of Illinois Urbana-Champaign under the supervision of Prof. Nicolás Yunes. I received my undergraduate degree from the Chennai Mathematical Institute.Research
Strong gravity, compact objects, and gravitational waves
I work on theoretical and numerical problems involving compact objects and gravitational waves. You can find a brief description of my research interests here.
Tides in neutron star binary systems
Relativistic mode sums
I am interested in developing a relativistic mode-sum description of neutron-star tidal response. This work clarifies how the familiar Newtonian picture of forced stellar oscillations extends to general relativity, how relativistic overlap integrals should be defined, and when a low-mode approximation accurately reproduces the full tidal response.
- Relativistic and Dynamical Love
- The Good, the Bad, and the Subtle: Relativistic mode sums for neutron-star tidal response
Dynamical tides
I have developed a relativistic formalism capable of incorporating dynamical tidal effects produced by the oscillation modes of neutron stars. I am interested in understanding how these frequency-dependent deformations depend on stellar structure and how they appear in gravitational-wave signals.
- Dynamical tidal response of non-rotating relativistic stars
- Dynamical tidal response of neutron stars as a probe of dense-matter properties
- Universal Relations with Dynamical Tides
Dissipative tides
I am developing tidal models that incorporate out-of-equilibrium effects such as shear and bulk viscosity. These models provide a way to use gravitational-wave observations to constrain transport coefficients and other dissipative properties of neutron-star matter.
- Probing internal dissipative processes of neutron stars with gravitational waves during the inspiral of neutron-star binaries
- A constraint on the dissipative tidal deformability of neutron stars
- Dissipative tidal effects to next-to-leading order and constraints on the dissipative tidal deformability using gravitational-wave data
- A New Spin on Dissipative Tides: First-Post-Newtonian Effects in Compact Binary Inspirals
Measuring the Hubble constant using neutron star binary systems
Gravitational wave measurements from binary neutron star mergers can be used to probe the large-scale structure of our universe. This is possible due to the dependence of the tidal deformabilities of neutron stars on the intrinsic mass, which breaks the redshift-mass degeneracy in the gravitational wave signal. To facilitate the measurement of the redshift using this technique, we need to understand the equation of state of a neutron star. One way to bypass this requirement is to use a quasi-universal relationship between neutron star tidal deformabilities which are approximately insensitive to the equation of state. I have worked on understanding how such quasi-universal relations can be used to constrain the value of the Hubble constant using present and future gravitational wave observations.
EMRI–disk interactions
Extreme mass-ratio inspirals (EMRIs) embedded in accretion disks provide a unique opportunity to study the interplay between strong-field gravity and astrophysical environments. My research focuses on developing relativistic perturbation-theory methods to compute the excitation of density waves by orbiting compact objects, including Lindblad and corotation resonances, the resulting angular-momentum exchange between the binary and the disk, and the impact of these interactions on gravitational-wave signals observable by LISA.
- Relativistic treatment of accretion disk torques on extreme mass-ratio inspirals around nonspinning black holes
- Relativistic treatment of accretion disk torques on extreme mass ratio inspirals around spinning black holes
Weakly collisional plasmas
Many astrophysical plasmas, including low-luminosity accretion flows around black holes, are only weakly collisional and might not be accurately described by ideal magnetohydrodynamics. My research develops relativistic kinetic and fluid models for these systems by deriving macroscopic evolution equations directly from kinetic theory. In particular, I am interested in pressure anisotropy, Landau damping, anisotropic heat transport, and fluid closures that capture collisionless plasma physics. These models provide a bridge between first-principles plasma physics and observations by the Event Horizon Telescope and future high-resolution black hole imaging experiments.
Mathematical properties and consistency of effective field theories of gravity
Gravitational wave observations offer an exciting opportunity to test the validity of general relativity in highly dynamical and strongly gravitating regions of spacetime. Several alternatives to general relativity have been proposed in the literature that present modifications to general relativity in strongly gravitating regions of spacetime by adding extra scalar, vector or tensorial degrees of freedom. To be viable, these theories have to be mathematically consistent in regions of strong curvature. One such mathematical requirement is that these extensions have to be hyperbolic partial differential equations. I have provided a precise criterion for testing when certain effective field theories of gravity breakdown in spherical symmetry .
Black holes in general relativity are completely described by the value of their mass and spin. Certain alternatives to general relativity also add additional scalar charges to black holes. These scalar charges are absent in neutron stars. Therefore, during a dynamical gravitational collapse, these scalar charges must develop spontaneously. I have investigated the mechanism behind the development of the scalar charge in spherical and axisymmetric gravitational collapse.