Cosmological coupling of nonsingular black holes

Abstract

We show that — in the framework of general relativity (GR) — if black holes (BHs) are singularity-free objects, they couple to the large-scale cosmological dynamics. We find that the leading contribution to the resulting growth of the BH mass (M BH) as a function of the scale factor a stems from the curvature term, yielding M BH ∝ ak , with k = 1. We demonstrate that such a linear scaling is universal for spherically-symmetric objects, and it is the only contribution in the case of regular BHs. For nonsingular horizonless compact objects we instead obtain an additional subleading model-dependent term. We conclude that GR nonsingular BHs/horizonless compact objects, although cosmologically coupled, are unlikely to be the source of dark energy. We test our prediction with astrophysical data by analysing the redshift dependence of the mass growth of supermassive BHs in a sample of elliptical galaxies at redshift z = 0.8–0.9. We also compare our theoretical prediction with higher redshift BH mass measurements obtained with the James Webb Space Telescope (JWST). We find that, while k = 1 is compatible within 1σ with JWST results, the data from elliptical galaxies at z = 0.8–0.9 favour values of k > 1. New samples of BHs covering larger mass and redshift ranges and more precise BH mass measurements are required to settle the issue.

Quasi-local masses and cosmological coupling of black holes and mimickers

“…Such objects are quiescent, i.e., they are concerned by negligible processes of accretion or mergers, so that the data-set is not sensibly affected by other growth channels other than the supposed coupling mechanism with the expanding background. This set of data showed a preference for k ∼ 3 [73,74]. The conclusion of the authors of ref.…”

“…We use here the same convention as in ref. [74], i.e., we define the surface of the object as the one containing 99% of the MS mass. Notice that there is no technical complication due to the presence of a time-dependent apparent horizon, which replaces the event horizon for the cosmologically embedded solutions.…”

“…However, in ref. [74], we and collaborators built a solid general relativistic framework that enabled us to describe the coupling of local inhomogeneities with the cosmological background in full generality, as well as to recover the expression of the mass-shift from refs. [70,73].…”

Constraints on Cosmological Coupling from the Accretion History of Supermassive Black Holes

“…cosmological constant (Croker & Weiner 2019;Farrah et al 2023a; see also Prescod-Weinstein et al 2009, for an alternative way BHs could be the origin of dark energy). In contrast, GR solutions for nonsingular BHs prefer k = 1 (Cadoni et al 2023b). In this case, the BH mass growth would not compensate for cosmological dilution of their density, so they would not contribute to dark energy.…”

“…Recently, however, it was realized that the masses of nonsingular BHs could be affected by the cosmic expansion (Croker & Weiner 2019). Indeed, in a recent paper, Cadoni et al (2023b) show that such a coupling is necessary in general relativity (GR) if BHs do not contain singularities. Thus the detection of a nonzero cosmological coupling would have important implications for our understanding of BHs.…”