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ABSTRACT We investigate the effect of the cutting-edge circumbinary disc (CBD) evolution models on massive black hole binary (MBHB) populations and the gravitational wave background (GWB). We show that CBD-driven evolution leaves a tell-tale signature in MBHB populations, by driving binaries towards an equilibrium eccentricity that depends on the binary mass ratio. We find high orbital eccentricities ($$e_{\rm b} \sim 0.5$$) as MBHBs enter multimessenger observable frequency bands. The CBD-induced eccentricity distribution of MBHB populations in observable bands is independent of the initial eccentricity distribution at binary formation, erasing any memory of eccentricities induced in the large-scale dynamics of merging galaxies. Our results suggest that eccentric MBHBs are the rule rather than the exception in upcoming transient surveys, provided that CBDs regularly form in MBHB systems. We show that the GWB amplitude is sensitive to CBD-driven preferential accretion onto the secondary, resulting in an increase in GWB amplitude $$A_{\rm yr^{-1}}$$ by over 100 per cent with just 10 per cent Eddington accretion. As we self-consistently allow for binary hardening and softening, we show that CBD-driven orbital expansion does not diminish the GWB amplitude, and instead increases the amplitude by a small amount. We further present detection rates and population statistics of MBHBs with $$M_{\rm b} \gtrsim 10^6 \, {\rm M}_{\odot }$$ in Laser Interferometer Space Antenna, showing that most binaries have equal mass ratios and can retain residual eccentricities up to $$e_{\rm b} \sim 10^{-3}$$ due to CBD-driven evolution.
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Disk-induced Binary Precession: Implications for Dynamics and Multimessenger Observations of Black Hole Binaries
Abstract Many studies have recently documented the orbital response of eccentric binaries accreting from thin circumbinary disks, characterizing the change in the binary semimajor axis and eccentricity. We extend these calculations to include the precession of the binary’s longitude of periapse induced by the circumbinary disk, and we characterize this precession continuously with binary eccentricityebfor equal mass components. This disk-induced apsidal precession is prograde with a weak dependence on the binary eccentricity wheneb≲ 0.4 and decreases approximately linearly foreb≳ 0.4; yet at allebbinary precession is faster than the rates of change to the semimajor axis and eccentricity by an order of magnitude. We estimate that such precession effects are likely most important for subparsec separated binaries with masses ≲107M⊙, like LISA precursors. We find that accreting, equal-mass LISA binaries withM< 106M⊙(and the most massiveM∼ 107M⊙binaries out toz∼ 3) may acquire a detectable phase offset due to the disk-induced precession. Moreover, disk-induced precession can compete with general relativistic precession in a vacuum, making it important for observer-dependent electromagnetic searches for accreting massive binaries—like Doppler boost and binary self-lensing models—after potentially only a few orbital periods.
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- Award ID(s):
- 2206299
- PAR ID:
- 10537736
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 964
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 46
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ad2613
