Two paths of cluster evolution: global expansion versus core collapse

O’Leary, Ryan M.; Stahler, Steven W.; Ma, Chung‐Pei

doi:10.1093/mnras/stu1455

Cited by 7 publications

(4 citation statements)

References 59 publications

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“…Unlike continuum models, in Nbody models (and real star clusters) this sequence is prevented by the presence of existing or newly formed binary stars in the core, whose ability to efficiently expel other stars via three-body interactions cools the core (e.g. Aarseth 1972;Hut 1983;Fujii & Portegies Zwart 2014;O'Leary et al 2014). The cluster core gradually shrinks towards the collapse and then expands rapidly (so called core bounce).…”

Section: Introductionmentioning

confidence: 99%

The hunt for self-similar core collapse

Pavlík

Šubr

2018

A&A

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Context. Core collapse is a prominent evolutionary stage of self-gravitating systems. In an idealised collisionless approximation, the region around the cluster core evolves in a self-similar way prior to the core collapse. Thus, its radial density profile outside the core can be described by a power law, ρ ∝ r −α . Aims. We aim to find the characteristics of core collapse in N-body models. In such systems, a complete collapse is prevented by transferring the binding energy of the cluster to binary stars. The contraction is, therefore, more difficult to identify. Methods. We developed a method that identifies the core collapse in N-body models of star clusters based on the assumption of their homologous evolution. Results. We analysed different models (equal-and multi-mass), most of which exhibit patterns of homologous evolution, yet with significantly different values of α : the equal-mass models have α ≈ 2.3, which agrees with theoretical expectations, the multi-mass models have α ≈ 1.5 (yet with larger uncertainty). Furthermore, most models usually show sequences of separated homologous collapses with similar properties. Finally, we investigated a correlation between the time of core collapse and the time of formation of the first hard binary star. The binding energy of such a binary usually depends on the depth of the collapse in which it forms, for example from 100 kT to 10 4 kT in the smallest equal-mass to the largest multi-mass model, respectively. However, not all major hardenings of binaries happened during the core collapse. In the multi-mass models, we see large transfers of binding energy of ∼ 10 4 kT to binaries that occur on the crossing timescale and outside of the periods of the homologous collapses.

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Section: Introductionmentioning

confidence: 99%

The hunt for self-similar core collapse

Pavlík

Šubr

2018

A&A

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“…Several studies in the literature deal with the evolution of open clusters within a Galactic model. Depending on the mechanisms being studied, which usually are internal to the cluster, the external potential can be simplified as much as needed (Gieles et al 2014;O'Leary et al 2014;Cai et al 2016); keeping the external potential simple allows focusing on an specific internal mechanism. Another reason to simplify the galactic potential is the fact that the implementation of a realistic galactic model into an N -body code becomes too complicated as well as computationally expensive.…”

Section: High-altitude Open Clusters: Crossing the Galacticmentioning

confidence: 99%

“…Finally, important advances have been done in this field thanks to observational and theoretical dynamical studies (most of them applied to globular clusters). From the theoretical point of view, two important complementary approaches have been employed to simulate a disk galaxy: steady potentials (e.g., Gieles et al 2014;O'Leary et al 2014;Cai et al 2016) and N -body simulations (e.g., Gieles et al 2006;Rieder et al 2013;Rossi et al 2016). While N -body simulations provide the only way to study galaxy and clusters evolution selfconsistently, steady potentials are fully adjustable, fast, able to represent a given galaxy (to the best of our observational knowledge of it), and provide orbital details that N -body simulations cannot do.…”

Section: Introductionmentioning

confidence: 99%

On the Survival of High-Altitude Open Clusters Within the Milky Way Galaxy Tides

Martinez-Medina

Pichardo

Peimbert

et al. 2017

ApJ

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It is a common assumption that high-altitude open clusters live longer compared with clusters moving close to the Galactic plane. This is because at high altitudes, open clusters are far from the disruptive effects of in-plane substructures, such as spiral arms, molecular clouds and the bar. However, an important aspect to consider in this scenario is that orbits of high-altitude open clusters will eventually cross the Galactic plane, where the vertical tidal field of the disk is strong. In this work we simulate the interaction of open clusters with the tidal field of a detailed Milky Way Galactic model at different average altitudes and galactocentric radii. We find that the life expectancy of clusters decreases as the maximum orbital altitude increases and reaches a minimum at altitudes of approximately 600 pc. Clusters near the Galactic plane live longer because they do not experience strong vertical tidal shocks from the Galactic disk; then, for orbital altitudes higher than 600 pc, clusters start again to live longer due to the decrease in the number of encounters with the disk. With our study, we find that the compressive nature of the tides in the arms region and the bar have an important role on the survival of small clusters by protecting them from disruption: clusters inside the arms can live up to twice as long as those outside the arms at similar galactocentric distance.

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“…Vesperini & Heggie 1997;Baumgardt & Makino 2003;Gill et al 2008), and the evolution of the cluster's stellar content, including the formation of binary stars while its central region undergoes core collapse (e.g. Aarseth 1972;Hut 1983;Fujii & Portegies Zwart 2014;O'Leary et al 2014;Pavlík & Šubr 2018). Primordial binaries play a key role in the structural development of a SC since they act as heating sources halting core collapse earlier and at lower densities (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Mass segregation and dynamics of primordial binaries in star clusters with a radially anisotropic velocity distribution

Pavlík,

Vesperini

2022

Preprint

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This paper is the third in a series investigating, by means of 𝑁-body simulations, the implications of an initial radially anisotropic velocity distribution on the dynamics of star clusters. Such a velocity distribution may be imprinted during a cluster's early evolutionary stages and several observational studies have found examples of old globular clusters in which radial anisotropy is still present in the current velocity distribution. Here we focus on its influence on mass segregation and the dynamics of primordial binary stars (disruptions, ejections, and component exchanges). The larger fraction of stars on radial/highly eccentric orbits in the outer regions of anisotropic clusters lead to an enhancement in the dynamical interactions between inner and outer stars that affects both the process of mass segregation and the evolution of primordial binaries. The results of our simulations show that the time scale of mass segregation of the initially anisotropic cluster is longer in the core and shorter in the outer regions, when compared to the initially isotropic system. The evolution of primordial binaries is also significantly affected by the initial velocity distribution and we find that the rate of disruptions, ejections and exchange events affecting the primordial binaries in the anisotropic clusters is higher than in the isotropic ones.

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Two paths of cluster evolution: global expansion versus core collapse

Cited by 7 publications

References 59 publications

The hunt for self-similar core collapse

The hunt for self-similar core collapse

On the Survival of High-Altitude Open Clusters Within the Milky Way Galaxy Tides

Mass segregation and dynamics of primordial binaries in star clusters with a radially anisotropic velocity distribution

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