Shadows of black holes at cosmological distances in the co-varying physical couplings framework

• Published in: Monthly notices of the Royal Astronomical Society Vol. 526; no. 3; pp. 3987 - 3993
• Main Authors: Cuzinatto, R R, de Melo, C A M, Neves, Juliano C S
• Format: Journal Article
• Language: English
• Published: Oxford University Press 10.10.2023
• Subjects: black hole physics; dark energy; distance scale; cosmology: theory
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad2954

ABSTRACT The co-varying physical couplings (CPC) framework states that physical parameters like the speed of light in vacuum c, the Newtonian constant G, and the cosmological constant Λ could indeed vary with the space–time coordinates xμ. Here, we assume a temporal variation, that is, c(t), G(t), and Λ(t). We show that the McVittie space–time, a black hole in an expanding universe, is a solution of the CPC framework providing naturally an important parameter of the model. Then, we calculate the shadow angular radius of this black hole at cosmological distances. A black hole shadow in the CPC context could be either larger or smaller than the same shadow in the standard cosmology. It depends on how the set {c, G, Λ} varies with time or with the cosmic expansion.