Constraints on Barrow entropy from M87* and S2 star observations

TL;DR

This study uses observational data from M87* and the S2 star to constrain Barrow entropy, a quantum-gravity-inspired modification of black hole entropy, deriving bounds on the parameter  with implications for black hole physics.

Contribution

First constraints on Barrow entropy parameter  derived from astrophysical observations of black hole shadow and stellar orbits.

Findings

Estimated  .6^{+0.0792}_{-0.0145}

Upper bound  \u2264 0.0828 at 17

Constraints are weaker than Big Bang Nucleosynthesis but stronger than late-time cosmology

Abstract

We use data from M87* central black hole shadow, as well as from the S2 star observations, in order to extract constraints on Barrow entropy. The latter is a modified entropy arising from quantum-gravitational effects on the black hole horizon, quantified by the new parameter $\Delta$. Such a change in entropy leads to a change in temperature, as well as to the properties of the black hole and its shadow. We investigate the photon sphere and the shadow of a black hole with Barrow entropy, and assuming a simple model for infalling and radiating gas we estimate the corresponding intensity. Furthermore, we use the radius in order to extract the real part of the quasinormal modes, and for completeness we investigate the spherical accretion of matter onto the black hole, focusing on isothermal and polytropic test fluids. We extract the allowed parameter region, and by applying a Monte-Carlo-Markov Chains analysis we find that $ \Delta \simeq 0.0036^{+0.0792}_{-0.0145}$. Hence, our results place the upper bound $\Delta\lesssim0.0828$ at 1$\sigma$, a constraint that is less strong than the Big Bang Nucleosynthesis one, but significantly stronger than the late-time cosmological constraints.