Semi-empirical framework of supermassive black hole evolution: highlighting a possible tension between demographics and gravitational wave background
The evolution of the supermassive Black Hole (BH) population across cosmic times remains a central unresolved issue in modern astrophysics, due to the many noticeable uncertainties in the involved physical processes that span a huge range of spatial, temporal and energy scales. Here we tackle the pr...
Saved in:
| Main Authors: | , , , , , , |
|---|---|
| Format: | Article (Journal) |
| Language: | English |
| Published: |
February 2, 2026
|
| In: |
Journal of cosmology and astroparticle physics
Year: 2026, Volume: 2026, Issue: 02, Pages: 1-55 |
| ISSN: | 1475-7516 |
| DOI: | 10.1088/1475-7516/2026/02/001 |
| Online Access: | Verlag, kostenfrei, Volltext: https://doi.org/10.1088/1475-7516/2026/02/001 Verlag, kostenfrei, Volltext: https://iopscience.iop.org/article/10.1088/1475-7516/2026/02/001 
|
| Author Notes: | Andrea Lapi, Francesco Shankar, Michele Bosi, Daniel Roberts, Hao Fu, Karthik M. Varadarajan and Lumen Boco |
| Summary: | The evolution of the supermassive Black Hole (BH) population across cosmic times remains a central unresolved issue in modern astrophysics, due to the many noticeable uncertainties in the involved physical processes that span a huge range of spatial, temporal and energy scales. Here we tackle the problem via a semi-empirical approach with minimal assumptions and data-driven inputs. This is based on a continuity plus Smoluchowski equation framework that allows to unitarily describe the two primary modes of BH growth: gas accretion and binary mergers. Key quantities related to the latter processes are incorporated through educated parameterizations, and then constrained in a Bayesian setup from joint observational estimates of the local BH mass function, of the large-scale BH clustering, and of the nano-Hz stochastic gravitational wave (GW) background measured from Pulsar Timimg Array (PTA) experiments. We find that the BH accretion-related parameters are strongly dependent on the local BH mass function determination: higher normalizations and flatter high-mass slopes in the latter imply lower radiative efficiencies and mean Eddington ratios with a stronger redshift evolution. Additionally, the binary BH merger rate is estimated to be a fraction ≲ 10-1 of the galaxy merger rate derived from galaxy pairs counts by JWST, and constrained not to exceed the latter at ≳ 2σ. Relatedly, we highlight hints of a possible tension between current constraints on BH demographics and the interpretation of the nano-Hz GW background as predominantly caused by binary BH mergers. Specifically, we bound the latter's contribution to ≲ 30-50% at ∼ 3σ, suggesting that either systematics in the datasets considered here have been underestimated so far, or that additional astrophysical/cosmological sources are needed to explain the residual part of the signal measured by PTA experiments. |
|---|---|
| Item Description: | Gesehen am 09.06.2026 |
| Physical Description: | Online Resource |
| ISSN: | 1475-7516 |
| DOI: | 10.1088/1475-7516/2026/02/001 |