Consistency of JWST black hole observations with NANOGrav gravitational wave measurements

¹ Theoretical Physics Department, CERN, Geneva, Switzerland
² King’s College London, Strand, London, WC2R 2LS, UK
³ Keemilise ja Bioloogilise Füüsika Instituut, Rävala pst. 10, 10143 Tallinn, Estonia
⁴ Departament of Cybernetics, Tallinn University of Technology, Akadeemia tee 21, 12618 Tallinn, Estonia
⁵ Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Via Marzolo 8, 35131 Padova, Italy
⁶ Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy

^★ Corresponding author; juan.urrutia@kbfi.ee

Received: 23 May 2024
Accepted: 30 September 2024

Abstract

JWST observations have opened a new chapter in supermassive black hole (SMBH) studies, stimulating discussion of two puzzles: the abundance of high-z SMBHs and the fraction of dual active galactic nuclei (AGNs). We argue that the answers to these puzzles may be linked to an interpretation of the data on the nanohertz gravitational waves (GWs) discovered by NANOGrav and other pulsar timing arrays as SMBH binaries whose evolution is driven by interactions with their environments down to O(0.1 pc) separations. We show that the stellar mass-black hole mass correlations found in JWST data and in low-ɀ inactive galaxies are similar, and present a global fit to these data, excluding low-ɀ AGNs. Matching the NANOGrav and dual-AGN data requires that binary evolution due to environmental effects at separations below O(1 kpc) be rapid on cosmological timescales. According to this interpretation, the SMBHs in low-ɀ AGNs are the tip of the iceberg of a local SMBH population in mainly inactive galaxies. This interpretation is consistent with the ‘little red dots’ observed with JWST being AGNs, and would favour the observability of GW signals from black hole binaries in LISA and decihertz GW detectors.