Unexpected formation modes of the first hard binary in core collapse

Tanikawa, Ataru; Hut, Piet; Makino, Junichiro

doi:10.1016/j.newast.2011.09.001

Cited by 27 publications

(22 citation statements)

References 19 publications

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“…This choice gives us a uniform set of initial conditions and, in any case, has little practical effect on the subsequent evolution. As has been shown in previous studies (e.g., Tanikawa, Hut & Makino 2012), and as we verify, central binaries rapidly form after the more massive cluster members drift to the center via dynamical friction.…”

Section: N -Body Simulationssupporting

confidence: 89%

Two paths of cluster evolution: global expansion versus core collapse

O’Leary

Stahler

2014

Monthly Notices of the Royal Astronomical Society

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All gravitationally bound clusters expand, due to both gas loss from their most massive members and binary heating. All are eventually disrupted tidally, either by passing molecular clouds or the gravitational potential of their host galaxies. However, their interior evolution can follow two very different paths. Only clusters of sufficiently large initial population and size undergo the combined interior contraction and exterior expansion that leads eventually to core collapse. In all other systems, core collapse is frustrated by binary heating. These clusters globally expand for their entire lives, up to the point of tidal disruption.Using a suite of direct N -body calculations, we trace the "collapse line" in r v − N space that separates these two paths. Here, r v and N are the cluster's initial virial radius and population, respectively. For realistic starting radii, the dividing N -value is from 10 4 to over 10 5 . We also show that there exists a minimum population, N min , for core collapse. Clusters with N < N min tidally disrupt before core collapse occurs. At the Sun's Galactocentric radius, R G = 8.5 kpc, we find N min 300. The minimum population scales with Galactocentric radius as R −9/8 G .The position of an observed cluster relative to the collapse line can be used to predict its future evolution. Using a small sample of open clusters, we find that most lie below the collapse line, and thus will never undergo core collapse. Most globular clusters, on the other hand, lie well above the line. In such a case, the cluster may or may not go through core collapse, depending on its initial size. We show how an accurate age determination can help settle this issue.

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Section: N -Body Simulationssupporting

confidence: 89%

Two paths of cluster evolution: global expansion versus core collapse

O’Leary

Stahler

2014

Monthly Notices of the Royal Astronomical Society

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“…Since the Yebisu code does not originally deal with no softened gravitational potential, we modify the code so that it supports no softening force shape. We also accelerate a search for neighbour particles around a given particle by using SIMD instructions, here Advanced Vector eXtensions (AVX), with Phantom-GRAPE for a collisional version (Tanikawa et al 2012a). We parallelise the calculation of gravitational forces with Message Passing Interface (MPI), such that we divide particles exerting gravitational forces on a given particle into MPI processes, which is so-called j-parallel algorithm.…”

Section: Methodsmentioning

confidence: 99%

Dynamical evolution of stellar mass black holes in dense stellar clusters: estimate for merger rate of binary black holes originating from globular clusters

Tanikawa

2013

Monthly Notices of the Royal Astronomical Society

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We have performed N -body simulations of globular clusters (GCs) in order to estimate a detection rate of mergers of Binary stellar-mass Black Holes (BBHs) by means of gravitational wave (GW) observatories. For our estimate, we have only considered mergers of BBHs which escape from GCs (BBH escapers). BBH escapers merge more quickly than BBHs inside GCs because of their small semi-major axes. N -body simulation can not deal with a GC with the number of stars N ∼ 10 6 due to its high calculation cost. We have simulated dynamical evolution of small-N clusters (10 4 N 10 5 ), and have extrapolated our simulation results to large-N clusters. From our simulation results, we have found the following dependence of BBH properties on N . BBHs escape from a cluster at each two-body relaxation time at a rate proportional to N . Semi-major axes of BBH escapers are inversely proportional to N , if initial mass densities of clusters are fixed. Eccentricities, primary masses, and mass ratios of BBH escapers are independent of N . Using this dependence of BBH properties, we have artificially generated a population of BBH escapers from a GC with N ∼ 10 6 , and have estimated a detection rate of mergers of BBH escapers by next-generation GW observatories. We have assumed that all the GCs are formed 10 or 12 Gyrs ago with their initial numbers of stars N i = 5 × 10 5 -2 × 10 6 and their initial stellar mass densities inside their half-mass radii ρ h,i = 6 × 10 3 -10 6 M ⊙ pc −3 . Then, the detection rate of BBH escapers is 0.5 -20 yr −1 for a BH retention fraction R BH = 0.5. A few BBH escapers are components of hierarchical triple systems, although we do not consider secular perturbation on such BBH escapers for our estimate. Our simulations have shown that BHs are still inside some of GCs at the present day. These BHs may marginally contribute to BBH detection.

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“…This is a good approximation as the majority of the relevant BBHs are believed to form dynamically through close interactions of > 2 initially unbound single BHs in the GC core [e.g. [83][84][85][86]; a process which has the highest probability of forming BBHs near a HB . We assume equal masses as both mass segregation and dynamical three-body swappings naturally lead to this limit [e.g.…”

Section: Modeling Black Hole Dynamicsmentioning

confidence: 99%

How post-Newtonian dynamics shape the distribution of stationary binary black hole LISA sources in nearby globular clusters

Samsing

D’Orazio

2019

Phys. Rev. D

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We derive the observable gravitational wave (GW) peak frequency (f ) distribution of binary black holes (BBHs) that currently reside inside their globular clusters (GCs), with and without 2.5 Post-Newtonian (2.5PN) effects included in the dynamical evolution of the BBHs. Recent Newtonian studies have reported that a notable number of nearby non-merging BBHs, i.e. those BBHs that are expected to undergo further dynamical interactions before merger, in GCs are likely to be observable by LISA. However, our 2.5PN calculations show that the distribution of log f for the non-merging BBH population above ∼ 10 −3.5 Hz scales as f −34/9 instead of the f −2/3 scaling found in the Newtonian case. This leads to an approximately two-orders-of-magnitude reduction in the expected number of GW sources at ∼ 10 −3 Hz, which lead us to conclude that observing nearby BBHs with LISA is not as likely as has been claimed in the recent literature. In fact, our results suggest that it might be more likely that LISA detects the population of BBHs that will merge before undergoing further interactions. This interestingly suggests that the BBH merger rate derived from LIGO can be used to forecast the number of nearby LISA sources, as well as providing insight into the fraction of BBH mergers forming in GCs. *

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Unexpected formation modes of the first hard binary in core collapse

Cited by 27 publications

References 19 publications

Two paths of cluster evolution: global expansion versus core collapse

Two paths of cluster evolution: global expansion versus core collapse

Dynamical evolution of stellar mass black holes in dense stellar clusters: estimate for merger rate of binary black holes originating from globular clusters

How post-Newtonian dynamics shape the distribution of stationary binary black hole LISA sources in nearby globular clusters

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