Observational implications of cosmologically coupled black holes

Ghodla, Sohan; Easther, Richard; Briel, M. M.; Eldridge, J. J.

doi:10.21105/astro.2306.08199

Cited by 8 publications

(5 citation statements)

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“…Conventional assumptions about SMBH accretion, combined with estimates of the local SMBH mass density based on the M • -M bulge relation, imply an allowed range of  <k 0 2 (Figure 2). This range is in slight tension (∼90% confidence interval) with the results in Farrah et al (2023a), though it is consistent with some of the recent constraints discussed in Section 1.2 (e.g., Rodriguez 2023;Andrae & El-Badry 2023;Ghodla et al 2023;Lei et al 2024).…”

Section: Discussionsupporting

confidence: 90%

“…However, Rodriguez (2023) disfavor coupling based on observations of a BH binary in the globular cluster NGC 3201 and Andrae & El-Badry (2023) argue that two BH binaries found by Gaia are likely to have formed with BH masses that were too small if k = 3. 4 Also, Ghodla et al (2023) argue that k = 3 would result in too many BH mergers compared to observations from gravitational-wave detectors.…”

Section: Cosmologically Coupled Black Holesmentioning

confidence: 99%

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

Lacy,

Engholm,

Farrah

et al. 2024

ApJL

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Coupling of black hole mass to the cosmic expansion has been suggested as a possible path to understanding the dark energy content of the Universe. We test this hypothesis by comparing the supermassive black hole (SMBH) mass density at z = 0 to the total mass accreted in active galactic nuclei (AGN) since z = 6, to constrain how much of the SMBH mass density can arise from cosmologically coupled growth, as opposed to growth by accretion. Using an estimate of the local SMBH mass density of ≈1.0 × 106 M ⊙ Mpc−1, a radiative accretion efficiency, η, in the range 0.05 < η < 0.3, and the observed AGN luminosity density at z ≈ 4, we constrain the value of the coupling constant between the scale size of the Universe and the black hole mass, k, to lie in the range 0 < k ≲ 2, below the value of k = 3 needed for black holes to be the source term for dark energy. Initial estimates of the gravitational-wave background (GWB) using pulsar timing arrays, however, favor a higher SMBH mass density at z = 0. We show that if we adopt such a mass density at z = 0 of ≈7.4 × 106 M ⊙ Mpc−1, this makes k = 3 viable even for low radiative efficiencies, and may exclude nonzero cosmological coupling. We conclude that, although current estimates of the SMBH mass density based on the black hole mass–bulge mass relation probably exclude k = 3, the possibility remains open that, if the GWB is due to SMBH mergers, k > 2 is preferred.

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Section: Discussionsupporting

confidence: 90%

Section: Cosmologically Coupled Black Holesmentioning

confidence: 99%

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

Lacy,

Engholm,

Farrah

et al. 2024

ApJL

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“…The forthcoming low-frequency gravitational wave detectors (e.g., LISA, Amaro-Seoane et al 2023) could detect these binaries and test whether the BH evolution is influenced by the expansion of the Universe. Considering the cosmologically coupled mass growth of BHs (assuming k = 3), Ghodla et al (2023) showed that the estimated rates of gravitational wave merger events would be 3 orders of magnitude higher than the observed rates. The LIGO-Virgo-KAGRA collaboration is currently conducting the O4 observing run.…”

Section: Discussionmentioning

confidence: 98%

“…Their results exclude k = 0 at 99.98% confidence and give k 3.11 1.33 1.19 = -+ at 90% confidence, consistent with vacuum energy (w = −1) interior BH models. These results have captured broad attention, with substantial discussions and comments available in the literature (e.g., Amendola et al 2023;Andrae & El-Badry 2023;Avelino 2023;Cadoni et al 2023;Ghodla et al 2023;Lei et al 2023;Mistele 2023;Parnovsky 2023, Wang & Wang 2023.…”

Section: Introductionmentioning

confidence: 96%

Can Cosmologically Coupled Mass Growth of Black Holes Solve the Mass Gap Problem?

Gao,

2023

ApJ

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Observations of elliptical galaxies suggest that black holes (BHs) might serve as dark energy candidates, coupled to the expansion of the Universe. According to this hypothesis, the mass of a BH could increase as the Universe expands. BH low-mass X-ray binaries (LMXBs) in the Galactic disk were born several gigayears ago, making the coupling effect potentially significant. In this work, we calculate the evolution of BH binaries with a binary population synthesis method to examine the possible influence of cosmologically coupled growth of BHs, if it really exists. The measured masses of the compact objects in LMXBs show a gap around ∼2.5–5 M ⊙, separating the most-massive neutron stars from the least-massive BHs. Our calculated results indicate that considering the mass growth seems to (partially) account for the mass gap and the formation of compact BH LMXBs, alleviating the challenges in modeling the formation and evolution of BH LMXBs with traditional theory. However, critical observational evidence like the detection of intermediate-mass BH binaries is required to test this hypothesis.

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“…Strikingly, these tests favour much smaller values of k, with a best-fit value of k ≃ −1. Moreover, a k = 3 cosmological coupling seems to be in tension with the predictions of the LIGO-Virgo-KAGRA network on the rate and typical masses of black hole mergers [18]. In view of this intricate situation, an exhaustive theoretical understanding of the cosmological coupling of BHs and other compact astrophysical objects is clearly crucial.…”

Section: Introductionmentioning

confidence: 98%

Cosmological coupling of nonsingular black holes

Cadoni,

Sanna,

Pitzalis

et al. 2023

J. Cosmol. Astropart. Phys.

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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.

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Observational implications of cosmologically coupled black holes

Cited by 8 publications

References 0 publications

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

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

Can Cosmologically Coupled Mass Growth of Black Holes Solve the Mass Gap Problem?

Cosmological coupling of nonsingular black holes

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