Research Interests
I work broadly in the areas of classical gravity and theoretical astrophysics.
I have recently been interested in experimental tests of classical gravity in the strong-field regime, up close to “hotly” accreting supermassive ultracompact objects such as black holes.
Towards this end, I have been involved in studying the impact of deviations from general relativity (non-Kerr black holes, non-black holes, violations of the equivalence principle, alternate actions, etc.) on actual images of such astrophysical sources, using analytic models for the accretion flow as well as with state-of-the-art general relativistic magnetohydrodynamics simulations.
Indeed, we have recently shown how the recently obtained images of the galactic nuclei M87* and Sgr A* by the Event Horizon Telescope can be used succesfully to constrain deviations from general relativity.
Now for the old highlights reel.
We investigated the potential for obtaining the spin of Sgr A* through the detection of galactic pulsars due to gravitomagnetism or frame-dragging, and found it to be very promising.
That superspinning compact objects can also be quasinormally stable was an interesting finding.
We were also invited to discuss a new perspective on the nonlinear stability of the Schwarzschild black hole spacetime from the point of view of gravitational collapse.
I am also slowly venturing into semiclassical gravity. I am also stoking an old flame: The collapse of stars to black holes and naked singularities, and the cosmic censorship conjecture.
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I am a member of the Event Horizon Telescope (EHT) and of the next-generation Event Horizon Telescope (ngEHT) collaborations.
I also co-lead the ngEHT Foundations Focus Group with Helen Meskhidze.
Highlights from My Latest Project
Extreme Light Bending in Black Hole Spacetimes: Strong-Field Tests of Gravity
Ref.: Kocherlakota, Rezzolla, Roy, Wielgus [arXiv:2307.16841]
The image on the left shows many distinct photon orbits in a nonrotating Schwarzschild black hole spacetime. Extreme light bending is clearly visible here as one moves across columns from left to right: Photons loop around the black hole more number of times!
This extreme light bending is expected to cause ultrasharp features to appear in a picture of a black hole, when taken at higher resolution.
Detecting these photon rings will help reveal new aspects of the spacetime geometry. In particular, it may become possible to measure the rate at which diverge from each other near the “photon shell” of a black hole.
This rate is governed by the critical lensing Lyapunov exponent, which is determined in terms of the spacetime geometry. This lensing exponent is entirely independent of the accretion physics that is a big part of the puzzle behind the astrophysics of black hole images. Thus, measuring this exponent gives us fundamentally new information about the spacetime geometry, opening up space for novel new experimental tests of gravity.
Photons that loop many times around the black hole take longer to arrive on the observer’s screen, when emitted at the same time as a photon that does not loop around the black hole at all. This time delay is also determined, to a large extent, by the spacetime geometry. Stay tuned for future work exposing tests of gravity in this direction.
CV
The Black Hole Initiative at Harvard University
I have been a fellow at the BHI from 2022. My research has expanded to include general relativistic magnetohydrodynamics simulations, which model the flow of hot magnetized plasma, in non-Kerr spacetimes. I am continuing to think about future experimental tests of gravity with future black hole imaging measurements. I am also going back to gravitational collapse, as well as exploring aspects of semi-classical gravity.
Dept. of Astronomy & Astrophysics at Tata Institute of Fundamental Research
I was a graduate student at TIFR-Mumbai from 2013-2019. I obtained my M.Sc. and Ph.D. in 2020. My Ph.D. thesis, entitled “On the Stability and Detection of Compact Objects in General Relativity,” can be found at this link.
Chapter 2 of my thesis, on the stability of spacetimes in general relativity, emerged from a set of lecture series I delivered at the wonderful 2019 ST4 Conference. One can find a neat exposition of metric-perturbation theory in curved spacetimes there.
The Institute for Theoretical Physics at University of Frankfurt
I was a postdoctoral fellow at the ITP from 2019-2022, and spent my time studying non-Kerr black hole spacetimes that arise in alternate theories of classical gravity and fields, such as in the low-energy effective limit of string theory. My underlying goal was to estimate the potential of experimental tests of gravity with the first high-resolution images of the accreting supermassive black holes M87* and Sgr A* obtained by the Event Horizon Telescope (EHT) Collaboration.
I also expended considerable efforts investigating several black hole parametrized metrics to enable complementary theory-agnostic null tests of strong-field gravity.
My contributions towards experimental tests of gravity with the first ever image of Sgr A*, the supermassive ultracompact object holding the Milky Way together, were recognized in 2022 by an EHT Early Career Award.
Dept. of Physics at Indian Institute of Technology-Madras
I spent four years from 2009-2013 at IIT-M and earned my B.Tech. in Engineering Physics.
My full CV can be found at this link.
Prashant Kocherlakota 