Prospects for future binary black hole gravitational wave studies in light of PTA 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
e-mail: juan.urrutia@kbfi.ee
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

Received: 28 February 2023
Accepted: 3 June 2023

Abstract

NANOGrav and other Pulsar Timing Arrays (PTAs) have discovered a common-spectrum process in the nHz range that may be due to gravitational waves (GWs): if so, they are likely to have been generated by black hole (BH) binaries with total masses > 10⁹ M_⊙. Using the Extended Press-Schechter formalism to model the galactic halo mass function and a simple relation between the halo and BH masses suggests that these binaries have redshifts z = 𝒪(1) and mass ratios ≳10, and that the GW signal at frequencies above 𝒪(10) nHz may be dominated by relatively few binaries that could be distinguished experimentally and would yield observable circular polarization. Extrapolating the model to higher frequencies indicates that future GW detectors such as LISA and AEDGE could extend the PTA observations to lower BH masses ≳10³ M_⊙.