# Tests of Loop Quantum Gravity from the EHT Results of Sgr A$^*$

**Authors:** Misba Afrin, Sushant G. Ghosh  
**arXiv:** [2209.12584](https://arxiv.org/abs/2209.12584)  
**Date:** 2022-09-26  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2209.12584v1/

## Key points

- The paper explores implications of the image of the supermassive black hole Sgr A$^*$ captured by the EHT collaboration.
- The shadow of Sgr A$^*$ has an angular diameter $d_{sh}= 48.7 \pm 7\,\mu$as and a fractional deviation $\delta= -0.08^{+0.09}_{-0.09}\,,-0.04^{+0.09}_{-0.10}$ from the Schwarzschild black hole shadow diameter.
- Two models, LIRBH-1 and LIRBH-2, introduce an additional deviation parameter $L_q$ related to quantum effects in black holes beyond the traditional Kerr metric.
- Non-Kerr black hole metrics offer singularity resolution and exhibit distinct shadow shapes compared to Kerr black holes.
- Analysis in Section 2 focuses on how varying $L_q$ impacts photon geodesics and shadow silhouettes of LIRBHs.
- Section 3 discusses estimating parameters like $L_q$, area ($A$), and oblateness ($D$) using shadow observables.
- Section 4 is dedicated to constraining $L_q$ based on bounds derived from EHT observations of shadow observables such as $d_{sh}$ and $\delta.
- Results provide upper bounds for $L_q$, indicating constraints on quantum effects in black holes.
- The study offers a detailed examination of how loop quantum gravity can be tested using observational data from Sgr A$^*$'s shadow, providing insights into gravitational physics near supermassive black holes.

## Summary

The paper "Tests of Loop Quantum Gravity from the EHT Results of Sgr A$^*$" explores the implications of the groundbreaking image of the supermassive black hole Sgr A$^*$ at the galactic center captured by the Event Horizon Telescope (EHT) collaboration. The shadow of Sgr A$^*$ has an angular diameter $d_{sh}= 48.7 \pm 7\,\mu$as and a fractional deviation $\delta= -0.08^{+0.09}_{-0.09}\,,-0.04^{+0.09}_{-0.10}$ from the Schwarzschild black hole shadow diameter, providing valuable insights into gravity in strong-field regimes. The study focuses on two well-established models, LIRBH-1 and LIRBH-2, which introduce an additional deviation parameter $L_q$ related to quantum effects in black holes beyond the traditional Kerr metric. These non-Kerr black hole metrics offer singularity resolution and exhibit distinct shadow shapes compared to Kerr black holes. Section 2 analyzes photon geodesics and shadow silhouettes of LIRBHs to explore how varying $L_q$ impacts these observables. In Section 3, the paper discusses estimating black hole parameters such as $L_q$, area ($A$), and oblateness ($D$) using shadow observables. Section 4 is dedicated to constraining $L_q$ based on bounds derived from EHT observations of shadow observables such as $d_{sh}$ and $\delta$. The results provide upper bounds for $L_q$, indicating constraints on quantum effects in black holes. Throughout the analysis, geometrized units are used unless specified otherwise for consistency purposes. This comprehensive study offers a detailed examination of how loop quantum gravity can be tested using observational data from Sgr A$^*$'s shadow, providing valuable insights into fundamental aspects of gravitational physics in extreme environments near supermassive black holes.