Binary--Single Star Interactions in Globular Clusters

Sigurd̵sson, Steinn; Phinney, E. S.

doi:10.1086/173190

Cited by 217 publications

(282 citation statements)

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“…The distribution of the eccentricity of the remaining binary is bell shaped around e = 0.3 for compact systems [44,45]. Classical studies [46] show that the probability of exchange of the binary companion in a triple system is surprisingly high for all comparable masses, reaching near one for more massive m 3 [47]. The motion of the system can be chaotic, due to small denominators.…”

Section: Figmentioning

confidence: 97%

Close encounters of three black holes

2008

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We present the first fully relativistic longterm numerical evolutions of three equal-mass black holes in a system consisting of a third black hole in a close orbit about a black-hole binary. We find that these close-three-black-hole systems have very different merger dynamics from black-hole binaries. In particular, we see complex trajectories, a redistribution of energy that can impart substantial kicks to one of the holes, distinctive waveforms, and suppression of the emitted gravitational radiation. We evolve two such configurations and find very different behaviors. In one configuration the binary is quickly disrupted and the individual holes follow complicated trajectories and merge with the third hole in rapid succession, while in the other, the binary completes a half-orbit before the initial merger of one of the members with the third black hole, and the resulting two-black-hole system forms a highly elliptical, well separated binary that shows no significant inspiral for (at least) the first t ∼ 1000M of evolution. Introduction: The recent dramatic breakthroughs in the numerical techniques to evolve black-hole-binary spacetimes [1, 2, 3] has led to rapid advancements in our understanding of black-hole physics. Notable among these advancements are developments in mathematical relativity, including systems of PDEs and gauge choices [4,5,6], the exploration of the cosmic censorship [7,8,9,10,11], and the application of isolated horizon formulae [8,9,12,13,14,15]. These breakthroughs have also influenced the development of data analysis techniques through the matching of post-Newtonian to fully-numerical waveforms [16,17,18]. Similarly, the recent discovery of very large merger recoil kicks [19,20,21,22,23,24,25,26] has had a great impact in the astrophysical community, with several groups now seeking for observational traces of such high speed holes as the byproduct of galaxy collisions [27,28]. In this letter, we continue our quest to discover new astrophysical consequences of black-hole interactions by simulating close encounters of three black holes to see the different behaviors introduced by the finite size of the holes, their nonlinear interactions, and the radiation of gravitational waves, as described by General Relativity. We find that the three-body relativistic problem shows far richer dynamics than the two-body problem, akin to the rich three-body dynamics in Newtonian gravity, but with added complexity due to mergers.

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Section: Figmentioning

confidence: 97%

Close encounters of three black holes

2008

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“…The trend toward energy equipartition in two-body interactions causes stars more massive than the mean mass to sink toward orbits deep in the cluster core, where they are very likely to come into direct interaction (and potentially partnership) with the IMBH (e.g., Gürkan et al 2004;Goswami et al 2012;Leigh et al 2014). Further, more massive secondary objects are likely to replace an existing companion if they do undergo a three-body interaction (Fullerton & Hills 1982;Sigurdsson & Phinney 1993;Mapelli & Zampieri 2014;Samsing et al 2014). In the lower right panel of Figure 4, we show the unnormalized distribution of companion masses in order to demonstrate that there is strong evolution in the companion mass distribution with stellar population age.…”

Section: Companion Stellar Propertiesmentioning

confidence: 99%

The Close Stellar Companions to Intermediate-Mass Black Holes

MacLeod

Trenti

Ramírez-Ruiz

2016

ApJ

109

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When embedded in dense cluster cores, intermediate-mass black holes (IMBHs) acquire close stellar or stellarremnant companions. These companions are not only gravitationally bound, but also tend to hierarchically isolate from other cluster stars through series of multibody encounters. In this paper we study the demographics of IMBH companions in compact star clusters through direct N-body simulations. We study clusters initially composed of 10 5 or 2×10 5 stars with IMBHs of 75 and 150 solar masses, and we follow their evolution for 6-10 Gyr. A tight, innermost binary pair of IMBH and stellar object rapidly forms. The IMBH has a companion with an orbital semimajor axis at least three times tighter than the second-most-bound object over 90% of the time. These companionships have typical periods on the order of years and are subject to cycles of exchange and destruction. The most frequently observed, long-lived pairings persist for ∼10 7 years. The demographics of IMBH companions in clusters are diverse: they include both main-sequence, giant stars and stellar remnants. Companion objects may reveal the presence of an IMBH in a cluster in one of several ways. The most-bound companion stars routinely suffer grazing tidal interactions with the IMBH, offering a dynamical mechanism to produce repeated flaring episodes like those seen in the IMBH candidate HLX-1. The stellar winds of companion stars provide a minimum quiescent accretion rate for IMBHs, with implications for radio searches for IMBH accretion in globular clusters. Finally, gravitational wave inspirals of compact objects occur with promising frequency.

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“…To test this possibility we perform numerical three-body scattering experiments (e.g. Hills & Fullerton 1980;Hut & Bahcall 1983;Sigurdsson & Phinney 1993;Heggie et al 1996;Gvaramadze et al 2008Gvaramadze et al , 2009Gvaramadze & Gualandris 2011) involving main-sequence stellar binaries and single stars/compact objects of different kinds. The simulations are carried out with the sigma3 package included in the STARLAB software environment .…”

Section: Acceleration In the Main-sequence Stagementioning

confidence: 99%

High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

Lützgendorf

Gualandris

Kissler-Patig

et al. 2012

A&A

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Context. We report the detection of five high-velocity stars in the core of the globular cluster NGC 2808. The stars lie on the red giant branch and show total velocities between 40 and 45 km s −1 . For a core velocity dispersion σ c = 13.4 km s −1 , this corresponds to up to 3.4σ c . These velocities are close to the estimated escape velocity (∼50 km s −1 ) and suggest an ejection from the core. Two of these stars have been confirmed in our recent integral field spectroscopy data and we will discuss them in more detail here. These two red giants are located at a projected distance of ∼0.3 pc from the center. According to their positions on the color magnitude diagram, both stars are cluster members. Aims. We investigate several possible origins for the high velocities of the stars and conceivable ejection mechanisms. Since the velocities are close to the escape velocity, it is not obvious whether the stars are bound or unbound to the cluster. We therefore consider both cases in our analysis. Methods. We perform numerical simulations of three-body dynamical encounters between binaries and single stars and compare the resulting velocity distributions of escapers with the velocities of our stars. If the stars are bound, the encounters must have taken place when the stars were still on the main sequence. We compare the predictions for a single dynamical encounter with a compact object with those of a sequence of two-body encounters due to relaxation. If the stars are unbound, the encounter must have taken place recently, when the stars were already in the giant phase. Results. After including binary fractions and black-hole retention fractions, projection effects, and detection probabilities from Monte-Carlo simulations, we estimate the expected numbers of detections for all the different scenarios. Based on these numbers, we conclude that the most likely scenario is that the stars are bound and were accelerated by a single encounter between a binary of main-sequence stars and a ∼10 M black hole. Finally, we discuss the origin of previously discovered fast stars in globular clusters, and conclude that the case of NGC 2808 is most likely a representative case for most other detections of fast stars in globular clusters. We show that with the present analysis we are able to explain high-velocity stars in the clusters M3 and 47 Tucanae with simple dynamical encounters.

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Binary--Single Star Interactions in Globular Clusters

Cited by 217 publications

References 0 publications

Close encounters of three black holes

Close encounters of three black holes

The Close Stellar Companions to Intermediate-Mass Black Holes

High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

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