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Testing Gravity Where It Is Strong

Lecturer: Prajwal Hassan Puttasiddappa, MSc (UFES and U. Oslo)

Schedule: July 14 to July 18 (5 classes), all at 10h00 (BRT)/13h00 (UTC).

Workload: 10h

Topics: What is strong-gravity regime? What are the observables in this regime? What are the tools to analyze the data? Are these tools independent of assumptions? What can we tell about the nature of gravity very close to black holes?

Overview: We explore modern techniques available for tests of gravity using stellar orbits and photon dynamics near the Galactic Center. We will analyze stellar motion and infer orbital parameters using both traditional Bayesian statistics and neural networks. We will also look at the possibility of using black hole shadow measurements to constrain deviations from Schwarzschild geometry. We will learn through hands-on exercises.

Pre-requisites: Introductory astronomy, basic Python and Mathematica.

Bibliography:

Detailed notes and codes, along with other references will be provided during the lectures.

Stellar Orbits around galactic center: We will use data from the paper “An Update on Monitoring Stellar Orbits in the Galactic Center” (S. Gillessen et al., The Astrophysical Journal 837, 30 (2017), arXiv: 1611.09144 [astro-ph.GA]) or through the catalog at this URL.

BH Shadows:

  1. Volker Perlick and Oleg Yu. Tsupko, “Calculating black hole shadows: Review of analytical studies,” Physics Reports 947, 1–39 (2022). arXiv: 2105.07101 [gr-qc].
  2. Gonzalo J. Olmo, João Luís Rosa, Diego Rubiera-Garcia, and Diego Sáez-Chillón Gómez, “Shadows and photon rings of regular black holes and geonic horizonless compact objects,” Classical and Quantum Gravity 40, 174002 (2023). arXiv: 2302.12064 [gr-qc].