scholarly journals Formation of counter-rotating and highly eccentric massive black hole binaries in galaxy mergers

2021 ◽  
Vol 503 (1) ◽  
pp. 498-510
Author(s):  
Imran Tariq Nasim ◽  
Cristobal Petrovich ◽  
Adam Nasim ◽  
Fani Dosopoulou ◽  
Fabio Antonini
Keyword(s):  
Black Hole ◽  
Gravitational Wave ◽  
Dynamical Evolution ◽  
Orbital Plane ◽  
Equal Mass ◽  
Galaxy Mergers ◽  
High Eccentricity ◽  
Massive Black Hole ◽  
Black Hole Binaries ◽  
Binary Evolution

ABSTRACT Supermassive black hole (SMBH) binaries represent the main target for missions such as the Laser Interferometer Space Antenna and Pulsar Timing Arrays. The understanding of their dynamical evolution prior to coalescence is therefore crucial to improving detection strategies and for the astrophysical interpretation of the gravitational wave data. In this paper, we use high-resolution N-body simulations to model the merger of two equal-mass galaxies hosting a central SMBH. In our models, all binaries are initially prograde with respect to the galaxy sense of rotation. But, binaries that form with a high eccentricity, e ≳ 0.7, quickly reverse their sense of rotation and become almost perfectly retrograde at the moment of binary formation. The evolution of these binaries proceeds towards larger eccentricities, as expected for a binary hardening in a counter-rotating stellar distribution. Binaries that form with lower eccentricities remain prograde and at comparatively low eccentricities. We study the origin of the orbital flip by using an analytical model that describes the early stages of binary evolution. This model indicates that the orbital plane flip is due to the torque from the triaxial background mass distribution that naturally arises from the galactic merger process. Our results imply the existence of a population of SMBH binaries with a high eccentricity and could have significant implications for the detection of the gravitational wave signal emitted by these systems.

scholarly journals Massive Black Hole Binaries: Dynamical Evolution and Observational Signatures

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
M. Dotti ◽  
A. Sesana ◽  
R. Decarli
Keyword(s):  
Black Hole ◽  
Galaxy Formation ◽  
Dynamical Evolution ◽  
Wave Spectra ◽  
Galaxy Mergers ◽  
Massive Black Hole ◽  
Theoretical Understanding ◽  
Black Hole Binaries ◽  
Recent Developments ◽  
Open Issues

The study of the dynamical evolution of massive black hole pairs in mergers is crucial in the context of a hierarchical galaxy formation scenario. The timescales for the formation and the coalescence of black hole binaries are still poorly constrained, resulting in large uncertainties in the expected rate of massive black hole binaries detectable in the electromagnetic and gravitational wave spectra. Here, we review the current theoretical understanding of the black hole pairing in galaxy mergers, with a particular attention to recent developments and open issues. We conclude with a review of the expected observational signatures of massive binaries and of the candidates discussed in literature to date.

scholarly journals Dynamical Evolution and Merger Timescales of LISA Massive Black Hole Binaries in Disk Galaxy Mergers

2018 ◽  
Vol 868 (2) ◽  
pp. 97 ◽  
Author(s):  
Fazeel M. Khan ◽  
Pedro R. Capelo ◽  
Lucio Mayer ◽  
Peter Berczik
Keyword(s):  
Black Hole ◽  
Dynamical Evolution ◽  
Disk Galaxy ◽  
Galaxy Mergers ◽  
Massive Black Hole ◽  
Black Hole Binaries

scholarly journals The Eccentric and Accelerating Stellar Binary Black Hole Mergers in Galactic Nuclei: Observing in Ground and Space Gravitational-wave Observatories

2021 ◽  
Vol 923 (2) ◽  
pp. 139
Author(s):  
Fupeng Zhang ◽  
Xian Chen ◽  
Lijing Shao ◽  
Kohei Inayoshi
Keyword(s):  
Black Hole ◽  
Gravitational Wave ◽  
Signal To Noise Ratio ◽  
Galactic Nuclei ◽  
Signal To Noise ◽  
High Eccentricity ◽  
Massive Black Hole ◽  
Binary Black Holes ◽  
Binary Black Hole ◽  
Space Observatories

Abstract We study the stellar binary black holes (BBHs) inspiraling/merging in galactic nuclei based on our numerical method GNC. We find that 3%–40% of all newborn BBHs will finally merge due to various dynamical effects. In a five-year mission, up to 104, 105, and ∼100 of BBHs inspiraling/merging in galactic nuclei can be detected with signal-to-noise ration >8 in Advanced LIGO (aLIGO), Einstein/DECIGO, and TianQin/LISA/TaiJi, respectively. Roughly tens are detectable in both LISA/TaiJi/TianQin and aLIGO. These BBHs have two unique characteristics. (1) Significant eccentricities: 1%–3%, 2%–7%, or 30%–90% of them have e i > 0.1 when they enter into aLIGO, Einstein, or space observatories, respectively. Such high eccentricities provide a possible explanation for that of GW190521. Most highly eccentric BBHs are not detectable in LISA/Tianqin/TaiJi before entering into aLIGO/Einstein, as their strain becomes significant only at f GW ≳ 0.1 Hz. DECIGO becomes an ideal observatory to detect those events, as it can fully cover the rising phase. (2) Up to 2% of BBHs can inspiral/merge at distances ≲103 r SW from the massive black hole, with significant accelerations, such that the Doppler phase drift of ∼10–105 of them can be detected with signal-to-noise ratio >8 in space observatories. The energy density of the gravitational-wave backgrounds (GWBs) contributed by these BBHs deviates from the power-law slope of 2/3 at f GW ≲ 1 mHz. The high eccentricity, significant accelerations, and the different profile of the GWB of these sources make them distinguishable, and thus interesting for future gravitational-wave detections and tests of relativities.

scholarly journals Stellar hardening of massive black hole binaries: the impact of the host rotation

2021 ◽  
Vol 508 (1) ◽  
pp. 1533-1542
Author(s):  
Ludovica Varisco ◽  
Elisa Bortolas ◽  
Massimo Dotti ◽  
Alberto Sesana
Keyword(s):  
Black Hole ◽  
Angular Momentum ◽  
Equal Mass ◽  
Stellar Systems ◽  
Massive Black Hole ◽  
Loss Cone ◽  
Black Hole Binaries ◽  
Influence Radius ◽  
Three Body ◽  
The Impact

ABSTRACT Massive black hole binaries (MBHBs) with masses of ∼104 to $\sim 10^{10} \, \mathrm{M}_{\odot {}}$ are one of the main targets for currently operating and forthcoming space-borne gravitational wave observatories. In this paper, we explore the effect of the stellar host rotation on the bound binary hardening efficiency, driven by three-body stellar interactions. As seen in previous studies, we find that the centre of mass (CoM) of a prograde MBHB embedded in a rotating environment starts moving on a nearly circular orbit about the centre of the system shortly after the MBHB binding. In our runs, the oscillation radius is ≈ 0.25 (≈ 0.1) times the binary influence radius for equal mass MBHBs (MBHBs with mass ratio 1:4). Conversely, retrograde binaries remain anchored about the centre of the host. The binary shrinking rate is twice as fast when the binary CoM exhibits a net orbital motion, owing to a more efficient loss cone repopulation even in our spherical stellar systems. We develop a model that captures the CoM oscillations of prograde binaries; we argue that the CoM angular momentum gain per time unit scales with the internal binary angular momentum, so that most of the displacement is induced by stellar interactions occurring around the time of MBHB binding, while the subsequent angular momentum enhancement gets eventually quashed by the effect of dynamical friction. The effect of the background rotation on the MBHB evolution may be relevant for LISA sources, that are expected to form in significantly rotating stellar systems.

scholarly journals The effect of differential accretion on the gravitational wave background and the present-day MBH binary population

2020 ◽  
Vol 498 (1) ◽  
pp. 537-547 ◽  
Author(s):  
Magdalena S Siwek ◽  
Luke Zoltan Kelley ◽  
Lars Hernquist
Keyword(s):  
Gravitational Wave ◽  
Analytical Models ◽  
Galaxy Mergers ◽  
Mass Ratio ◽  
Massive Black Hole ◽  
Black Hole Binaries ◽  
Pulsar Timing ◽  
Coalescence Rate ◽  
Gravitational Wave Background ◽  
First Time

ABSTRACT Massive black hole binaries (MBHBs) form as a consequence of galaxy mergers. However, it is still unclear whether they typically merge within a Hubble time, and how accretion may affect their evolution. These questions will be addressed by pulsar timing arrays (PTAs), which aim to detect the gravitational wave (GW) background (GWB) emitted by MBHBs during the last Myr of inspiral. Here, we investigate the influence of differential accretion on MBHB merger rates, chirp masses, and the resulting GWB spectrum. We evolve an MBHB sample from the Illustris hydrodynamic cosmological simulation using semi-analytical models and for the first time self-consistently evolve their masses with binary accretion models. In all models, MBHBs coalesce with median total masses up to 1.5 × 108 M⊙, up to 3−4 times larger than in models neglecting accretion. In our model with the largest plausible impact, the median mass ratio of coalescing MBHBs increases by a factor 3.6, the coalescence rate by $52.3{{\ \rm per\ cent}}$, and the GWB amplitude by a factor 4.0, yielding a dimensionless GWB strain $A_{yr^{-1}} = 1 \times 10^{-15}$. Our model that favours accretion on to the primary MBH reduces the median mass ratio of coalescing MBHBs by a factor of 2.9, and yields a GWB amplitude $A_{yr^{-1}} = 3.1 \times 10^{-16}$. This is nearly indistinguishable from our model neglecting accretion, despite higher MBHB masses at coalescence. We further predict binary separation and mass ratio distributions of stalled MBHBs in the low-redshift Universe, and find that these depend sensitively on binary accretion models. This presents the potential for combined electromagnetic and GW observational constraints on merger rates and accretion models of MBHB populations.

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