Selection bias in dynamically measured supermassive black hole samples: consequences for pulsar timing arrays

Sesana, Alberto; Shankar, Francesco; Bernardi, Mariangela; Sheth, Ravi K.

doi:10.1093/mnrasl/slw139

Cited by 78 publications

(91 citation statements)

References 50 publications

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“…This includes varying the GW spectrum amplitude A gw , which we have taken to be A gw = 10 −15 in the simulations in Sec. V. This is near the current limit placed by PTAs and coincides with models by Sesana [26] and Ravi et al [27]; however, recent work suggests the actual background may be a factor of 2 or 3 smaller [18,19,28]. A decrease in A gw will have a significant effect on the detection of GWs, as it will decrease the SNR and increase the amount of observation time needed to enter the intermediate-signal regime.…”

Section: Discussionsupporting

confidence: 84%

Supermassive black hole binary environments: Effects on the scaling laws and time to detection for the stochastic background

Vigeland

Siemens

2016

Phys. Rev. D

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One of the primary gravitational wave (GW) sources for pulsar timing arrays (PTAs) is the stochastic background formed by supermassive black holes binaries (SMBHBs). In this paper, we investigate how the environments of SMBHBs will effect the sensitivity of PTAs by deriving scaling laws for the signal-to-noise ratio (SNR) of the optimal cross-correlation statistic. The presence of gas and stars around SMBHBs will accelerate the merger at large distances, depleting the GW stochastic background at low frequencies. We show that environmental interactions may delay detection by a few years or more, depending on the PTA configuration and the frequency at which the dynamical evolution transitions from being dominated by environmental effects to GW-dominated.

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Section: Discussionsupporting

confidence: 84%

Supermassive black hole binary environments: Effects on the scaling laws and time to detection for the stochastic background

Vigeland

Siemens

2016

Phys. Rev. D

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“…If detection prospects increase as expected, in ~5 years one could detect a GW background with an amplitude of = 5 × 10 −16 , enabling us to probe a GW background generated from stalled SMBHBs, merging through subsequent manybody BH interactions [11,12]. In 6 years, one may be able to determine if in fact supermassive black hole masses have really been overestimated [15]. Importantly, both [11] and [12] show that there is a floor to the GWB at around = 10 −16 .…”

Section: The Next 10 Yearsmentioning

confidence: 86%

Probing supermassive black hole binaries with pulsar timing

Mingarelli

2019

Nat Astron

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The observation of gravitational-waves from merging supermassive black holes will be transformative: the detection of a low-frequency gravitational-wave background can tell us if and how supermassive black holes merge, inform our knowledge of galaxy merger rates and supermassive black hole masses, and enable the possibility of detecting new physics at nanohertz frequencies. All we have to do is time pulsars.Supermassive black hole (SMBH) mergers are the strongest sources of gravitational-waves (GWs) in the Universe. SMBH mergers are expected to follow galaxy mergers, since likely all massive galaxies host central SMBH, e.g. [1]. Briefly, the black holes fall to the center of the newly-formed galaxy through dynamical friction and form a binary. This binary should harden by ejecting stars crossing their orbit -a process called stellar hardening. When the binary is separated by a centiparsec to a milliparsec, gravitational waves (GWs) drive the binary to merge. These steps are described in more detail in [2].However, there is currently sparse observational evidence for sub-parsec separated SMBHB systems. In fact, under the assumption of a static spherical galaxy model, SMBHBs may stall at their final parsec of separation, and never merge -this is known as the final parsec problem [3]. This stalling happens when, for example, the black holes run out of stars to eject -called loss cone depletion. Even though the system is emitting GWs, it would take longer than a Hubble time for the binary to merge via GW emission only. However, if one assumes a triaxial galactic model, loss cone depletion is no longer an issue [4].There are other ways to overcome the final parsec problem: a circumbinary accretion disk can torque the binary, carrying away energy and angular momentum, helping it to overcome its final parsec of separation and merge. Environmental interactions with gas and stars also induce eccentricity in the binary [5]. An eccentric binary will emit GWs at higher harmonics, rapidly decreasing the time to coalescence of the binary, and enabling it to merge within a Hubble time. Pulsar Timing ArraysA pulsar timing array (PTA) is a galactic-scale GW detector. With an array of millisecond pulsars, one can search for nanohertz frequency GW signals originating from the most massive SMBHB systems in their slow inspiral phase, Refs [6,7]. GWs transiting the galaxy change the proper distance between the pulsars and the Earth by tens of meters per light year, inducing delays or advances in the pulsar's pulse arrival times. These time delays are tens to hundreds of nanoseconds over a decade, highlighting the importance of millisecond pulsars as the basis of our experiment: no other natural object has this kind of timing precision.The nanohertz GWs in the PTA band likely originate from SMBHBs in the 10 8 − 10 9 ⊙ range, with periods of years to decades, hence, they are millions of years from merging. A nanohertz GW background should be generated from the cosmic merger history of SMBHs and will likely be

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“…The impact of this bias on detection of GWs by PTAs was analyzed in [35]. Both of these studies accept at face value claims that SBH influence radii have been resolved.…”

Section: Discussionmentioning

confidence: 98%

“…(35) to express the relations (34) in terms of η, so that the η part of the merger rate distribution function The nonrotating model from which the rotating models were generated by orbit-flipping was described by Dehnen's [4] density law with γ = 1 and with an assumed SBH mass of 0.002M gal . Right: two distributions of η used in this paper (see Eq.36 and 34).…”

Section: Nuclear Rotationmentioning

confidence: 99%

Evolution of massive black hole binaries in rotating stellar nuclei: Implications for gravitational wave detection

Rasskazov

Merritt

2017

Phys. Rev. D

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We compute the isotropic gravitational wave (GW) background produced by binary supermassive black holes (SBHs) in galactic nuclei. In our model, massive binaries evolve at early times via gravitational-slingshot interaction with nearby stars, and at later times by the emission of GWs. Our expressions for the rate of binary hardening in the "stellar" regime are taken from the recent work of Vasiliev et al., who show that in the non-axisymmetric galaxies expected to form via mergers, stars are supplied to the center at high enough rates to ensure binary coalescence on Gyr timescales. We also include, for the first time, the extra degrees of freedom associated with evolution of the binary's orbital plane; in rotating nuclei, interaction with stars causes the orientation and the eccentricity of a massive binary to change in tandem, leading in some cases to very high eccentricities (e > 0.9) before the binary enters the GW-dominated regime. We argue that previous studies have overestimated the mean ratio of SBH mass to galaxy bulge mass by factors of 2 -3. In the frequency regime currently accessible to pulsar timing arrays (PTAs), our assumptions imply a factor 2 -3 reduction in the characteristic strain compared with the values computed in most recent studies, removing the tension that currently exists between model predictions and the non-detection of GWs.

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Selection bias in dynamically measured supermassive black hole samples: consequences for pulsar timing arrays

Cited by 78 publications

References 50 publications

Supermassive black hole binary environments: Effects on the scaling laws and time to detection for the stochastic background

Supermassive black hole binary environments: Effects on the scaling laws and time to detection for the stochastic background

Probing supermassive black hole binaries with pulsar timing

Evolution of massive black hole binaries in rotating stellar nuclei: Implications for gravitational wave detection

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