Scalaron Gravity near Sagittarius A*: Investigation of Spin of the Black Hole and Observing Requirements

Abstract

In this paper the author applies the scalaron gravity field and corresponding Yukawa coupling (derived by Kalita from the consideration of quantum vacuum fluctuations with UV and IR scales) to examine the scales of stellar orbits near the Galactic Center black hole, which can be probed by upcoming astrometric facilities for constraining modified gravity. Through the assumption that the pericenter shift of stellar orbits becomes of the order of spin and quadrupole moment effects of the black hole, it is found that for semimajor axes bounded below by time scales of gravitational wave emission and stellar age and above by S-2 like orbits (a = 990 au) the black hole spin with 0.1 ≤ χ ≤ 0.980 is eligible to probe scalaron masses within (10−22–10−18) eV and also the scalaron coupling, α = 2.73 × 10−4 derived earlier from quantum vacuum fluctuations. The orbital eccentricities are considered as e = 0.1, 0.5, and 0.9. Astrometric categories with σ = 10, 50, and 100 μas are used to probe the time scales and number of observing campaigns required for simultaneously constraining scalaron mass and black hole spin. It is found that extraction of black hole spin is possible within a = (74–433) au through 10 μas facilities. The present analysis is realized to be an independent opportunity to simultaneously constrain scalaron coupling, black hole spin, and tidal charge and hence to reveal the true nature of the spacetime structure of our nearest supermassive black hole.

Constraining primordial black hole masses through f(R) gravity scalarons in Big Bang Nucleosynthesis

“…These are known as scalarons. Scalarons as natural outcome of curvature corrections to quantum vacuum fluctuations near the Galactic Centre black hole have been used to forecast testability of modified gravity through pericentre shift of compact stellar orbits near the black hole and to investigate the effect of modified gravity on constraining spin of the black hole [37,38]. In these works the scalaron degree of freedom was shown to present a Yukawa type correction to gravitational potential near the black hole which affects the orbital shift of stars encircling the black hole in compact orbits.…”

“…Mass of the scalaron has been related to ultraviolet (UV) and infrared (IR) cut off scales of vacuum fluctuations near the black hole [37]. Possibility of constraining f (R) gravity theories through measurements near the Galactic Centre black hole has been extensively studied in earlier investigations [37][38][39][40][41][42]. Cosmological tests of f (R) gravity theories have been discussed earlier through large scale structure probes such as halo mass function [43,44], mass-temperature relation of galaxy clusters [45], cluster gas mass fraction [46] and clustering of clusters [47].…”

“…The 'Psi-Phi' plot (as we call it in this paper) is shown in figure 1 (Right). We wish to name it as LPTK-Psi-Phi plot for the authors Lalremruati (see [102] for the use of 'Psi-Phi' plot in the investigation of effect of dark matter on screening of scalarons near the Galactic Centre black hole), Paul (see [103] who investigated testability of unscreened scalarons near the orbit of the S-2 star orbiting the Galactic Centre black hole), Talukdar (one of us in this paper who generated this plot for PBHs) and Kalita (see [37,38] for first reports of testability of scalarons near the Galactic Centre black hole through existing and upcoming astrometric facilities employed for measuring pericentre shift of compact stellar orbits near the black hole). It is seen that scalarons corresponding to the above considered PBH mass range are all unscreened in the BBN era which indicates that there JCAP02(2024)019 is possibility to constrain them and thereby the PBH masses through their influence on the BBN process.…”

Motion of spinning particles around electrically charged black hole in Eddington-inspired Born–Infeld gravity

“…Besides the orbital and spin angular momentum of the test particle, the spin angular momentum of the central supermassive black hole can also affect the orbits of the stars around itself. However, there are no solid measurements for the spin of the supermassive black hole in the center of Sagittarius A* and the spin can be in the range of (0.1,0.98) [100][101][102][103][104]. Under such larger error of spin, we only consider the spinless case for the central spuermassive black hole to naively estimate the magnitude of κ.…”

Effect of Dark Matter Distribution on Scalaron Gravity near the Galactic Center Black Hole and Its Prospects

“…Pericenter shift of compact stellar orbits near the black hole in f(R) gravity has been estimated by several authors (Borka et al 2012(Borka et al , 2021Kalita 2020). In Kalita (2020Kalita ( , 2021 testability of these theories by astrometric facilities of existing and upcoming large telescopes has been discussed in a model-independent way (irrespective of the form of f(R)). In Lalremruati & Kalita (2022) it has been examined whether the breaking point of GR due to the scalaron effect becomes visible within the orbit of the S-2 star.…”