Inspiraling massive black hole binaries (MBHBs) forming in the aftermath of galaxy mergers are expected to be the loudest gravitational-wave (GW) sources relevant for pulsar-timing arrays (PTAs) at nHz frequencies. The incoherent overlap of signals from a cosmic population of MBHBs gives rise to a stochastic GW background (GWB) with characteristic strain around h c ~ 10 -15 at a reference frequency of 1 yr -1 , although uncertainties around this value are large. Current PTAs are piercing into theGWamplitude range predicted by MBHB-population models, but no detection has been reported so far. To assess the future success prospects of PTA experiments, it is therefore important to estimate the minimum GWB level consistent with our current understanding of the formation and evolution of galaxies and massive black holes (MBHs). To this purpose, we couple a semi-analytic model of galaxy evolution and an extensive study of the statistical outcome of triple MBH interactions. We show that even in the most pessimistic scenario where all MBHBs stall before entering the GW-dominated regime, triple interactions resulting from subsequent galaxy mergers inevitably drive a considerable fraction of the MBHB population to coalescence. At frequencies relevant for PTA, the resulting GWB is only a factor of 2-3 suppressed compared to a fiducial model where binaries are allowed to merge over Gyr time-scales. Coupled with current estimates of the expected GWB amplitude range, our findings suggest that the minimum GWB from cosmic MBHBs is unlikely to be lower than h c ~ 10 -16 (at f = 1 yr -1 ), well within the expected sensitivity of projected PTAs based on future observations with FAST, MeerKAT, and SKA. © 2018 The Author(s).

Post-Newtonian evolution of massive black hole triplets in galactic nuclei - III. A robust lower limit to the nHz stochastic background of gravitational waves / Bonetti, M.; Sesana, A.; Barausse, E.; Haardt, F.. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - 477:2(2018), pp. 2599-2612. [10.1093/mnras/sty874]

Post-Newtonian evolution of massive black hole triplets in galactic nuclei - III. A robust lower limit to the nHz stochastic background of gravitational waves

Barausse, E.;
2018

Abstract

Inspiraling massive black hole binaries (MBHBs) forming in the aftermath of galaxy mergers are expected to be the loudest gravitational-wave (GW) sources relevant for pulsar-timing arrays (PTAs) at nHz frequencies. The incoherent overlap of signals from a cosmic population of MBHBs gives rise to a stochastic GW background (GWB) with characteristic strain around h c ~ 10 -15 at a reference frequency of 1 yr -1 , although uncertainties around this value are large. Current PTAs are piercing into theGWamplitude range predicted by MBHB-population models, but no detection has been reported so far. To assess the future success prospects of PTA experiments, it is therefore important to estimate the minimum GWB level consistent with our current understanding of the formation and evolution of galaxies and massive black holes (MBHs). To this purpose, we couple a semi-analytic model of galaxy evolution and an extensive study of the statistical outcome of triple MBH interactions. We show that even in the most pessimistic scenario where all MBHBs stall before entering the GW-dominated regime, triple interactions resulting from subsequent galaxy mergers inevitably drive a considerable fraction of the MBHB population to coalescence. At frequencies relevant for PTA, the resulting GWB is only a factor of 2-3 suppressed compared to a fiducial model where binaries are allowed to merge over Gyr time-scales. Coupled with current estimates of the expected GWB amplitude range, our findings suggest that the minimum GWB from cosmic MBHBs is unlikely to be lower than h c ~ 10 -16 (at f = 1 yr -1 ), well within the expected sensitivity of projected PTAs based on future observations with FAST, MeerKAT, and SKA. © 2018 The Author(s).
477
2
2599
2612
https://academic.oup.com/mnras/article/477/2/2599/4963759
Bonetti, M.; Sesana, A.; Barausse, E.; Haardt, F.
File in questo prodotto:
File Dimensione Formato  
Bonetti_Sesana_Barausse.pdf

accesso aperto

Tipologia: Documento in Post-print
Licenza: Non specificato
Dimensione 4.13 MB
Formato Adobe PDF
4.13 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/89654
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 31
  • ???jsp.display-item.citation.isi??? 31
social impact