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2018ApJ...855...70K - Astrophys. J., 855, 70-70 (2018/March-1)

Gravitational theories near the Galactic Center.


Abstract (from CDS):

Upcoming Extremely Large Telescopes (ELTs) are promising probes of gravity in or near the galactic center (GC). Effects of alternative theories of gravity, namely the Brans-Dicke theory (BDT) and f(R) gravity, are studied near the GC black hole by calculating departure from general relativity (GR) in periastron advance of the S stars and light deflection. For these estimations, black hole spin and quadrupole moments are taken in the ranges χ = 0.1-2.0 and J2=10–6–2.0, respectively. Periastron advance ({dot}θprec) has been calculated for hypothetical S stars with orbital period one-fifth of S0-2 and eccentricity e = 0.8. The difference between BDT and GR (Δth{dot}θprec) lies in the range 10–3-2.3 µas yr–1, even for a large departure from GR. The difference between quadrupoles J2=10–6 and J2 = 2.0 lies in the range ΔJ2_{dot}θprec=0.268–0.281µasyr–1. These ranges are not only outside the astrometric capability of the ELTs, but are also contaminated by stellar perturbations. Parameter degeneracy among χ, J2, and ωBD is discussed. For black hole-S-star distances, DLS = 100 and 50 au, the difference in light deflection between BDT and GR lies in the range d(δφ)defl=10–5–10–1µas, making it difficult to distinguish them. From the relation between scalaron mass, Mψ in f(R) gravity, and calculated d(δφ)defl, it is found that Mψ=10–18–10–17eV can form a stable "dark cloud" near the black hole. Scalarons with 10–21eV are found to bring d(δφ)defl close to the astrometric range of the ELTs. Prospects for these scalarons in the tests of gravity are discussed.

Abstract Copyright: © 2018. The American Astronomical Society. All rights reserved.

Journal keyword(s): astrometry - black hole physics - Galaxy: center

Simbad objects: 6

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