Constraints on Barrow Entropy from M87* and S2 Star Observations

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 Δ. 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 Δ≃0.0036−0.0145+0.0792. Hence, our results place the upper bound Δ≲0.0828 at 1σ, a constraint that is less strong than the Big Bang Nucleosynthesis one, but significantly stronger than the late-time cosmological constraints.

Baryon asymmetry from Barrow entropy: theoretical predictions and observational constraints

“…As we can observe, if we desire the baryon asymmetry to originate from the effects of the Barrow entropy in the Friedmann equations, we must require 0.005 ∆ 0.008. This interval is tighter than the one arising from cosmological datasets from Supernovae (SNIa) Pantheon sample and cosmic chronometers, namely ∆ = 0.0094 +0.094 −0.101 [40,41], as well as from the one obtained from M87* and S2 star observations, namely ∆ = 0.0036 +0.0792 −0.0145 [43], and it is slightly wider than the one from Big Bang Nucleosynthesis (BBN), i.e. ∆ 10 −4 [42].…”

“…Additionally, one can apply Barrow entropy to the holographic principle, obtaining Barrow holographic dark energy [35][36][37][38][39]. Hence, one can confront the above constructions with observational data end amongst others extract constraints on the Barrow exponent ∆ [40][41][42][43]. As expected, in all these studies deviations from the BH entropy are found to be relatively small.…”

“…Finally, since the Barrow exponent has been found by various studies to satisfy ∆ 1 [40][41][42][43], which is expected since Barrow entropy should not deviate significantly from Bekenstein-Hawking one, we can expand the above expression resulting to…”

Barrow holographic dark energy with Granda-Oliveros cut-off

“…Furthermore, in [14] the authors used observational data from Supernovae (SNIa) Pantheon sample, as well as from direct measurements of the Hubble parameter from the cosmic chronometers (CC) sample, in order to extract constraints on the scenario of Barrow holographic dark energy. It is important to notice that the BHDE has been widely studied in the literature, e.g., [15][16][17][18][19][20][21][22][23][24][25][26].…”

Power-law holographic dark energy and cosmology

“…The first is to apply different horizons for the Universe, such as the event horizon, the apparent horizon, the age of the universe, the conformal time, the inverse square root of the Ricci curvature and the Gauss Bonnet term, etc [34][35][36][37][38][39][40][41][42][43][44][45]. On the other hand, the second possibility of modification is the consideration of a modified entropy expression for the Universe horizon instead of the standard Bekenstein-Hawking one, such as Tsallis entropy, Barrow entropy, Kaniadakis entropy, logarithmic corrected entropy etc [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64].…”