Physics Seminar
Date: Friday, 24 January 2025
Time: 1:45 PM
Venue: Lecture Hall 3
New Insights into Strong Gravity from Accreting Supermassive Black Holes
Prashant Kocherlakota
Harvard University.
24-01-25

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Abstract

Recent Event Horizon Telescope (EHT) images of Messier 87* and Sagittarius A* have been used to demonstrate that their spacetimes are well-described by the Kerr metric. The latter is a solution to the vacuum Einstein equations of general relativity and is used to describe spinning black holes. While of fundamental importance, the Kerr solution has undesirable features such as a spacetime singularity or a Cauchy horizon. Several phenomenological models that eliminate some of these features have been proposed, and confronting them with EHT measurements provides useful feedback to direct theoretical efforts. We will begin by briefly reviewing the current status of EHT observational constraints on such alternatives. We will then demonstrate how future Black Hole Explorer (BHEX) observations of the "photon ring" can grant access to new observables that will further refine our physical understanding of black holes. Lastly, the next generation EHT (ngEHT) experiment will produce resolved movies of the base of the jet in M87. Time permitting, we will also touch on how such jets are powered by black holes, as described universally by the Blandford-Znajek mechanism, an electromagnetic Penrose process.