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Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.


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TL;DR: In this paper, the authors studied the long term dynamical evolution of stellar mass black holes (BHs) at the Galactic center (GC) and put constraints on their number and central mass distribution.
Abstract: We study the long term dynamical evolution of stellar mass black holes (BHs) at the Galactic center (GC) and put constraints on their number and central mass distribution. Models of the GC are considered that have not yet achieved a steady state under the influence of random gravitational encounters. Contrary to some recent claims that mass-segregation can rapidly rebuild a density cusp in the stars, we find that time scales associated with cusp regrowth are longer than the Hubble time. These results cast doubts on standard models that postulate high densities of BHs near the GC and motivate studies that start from initial conditions which correspond to well-defined physical models. For the first time, we consider the distribution of BHs in a dissipationless formation model for the Milky Way nuclear cluster (NC), in which massive stellar clusters merge in the GC to form a nucleus. We simulate the successive inspiral of massive clusters containing an inner dense cluster of BHs. The pre-existing mass segregation is not completely erased as the clusters are disrupted by the massive black hole tidal field. As a result, after 12 inspiral events a NC forms in which the BHs have higher central densities than the stars. After evolving the model for 5-10 Gyr, the BHs do form a steep central cusp, while the stellar distribution maintains properties that resemble those of the Milky Way NC. Finally, we investigate the effect of BH perturbations on the motion of the GC S-stars, as a means of constraining the number of the perturbers. We find that reproducing the S-star orbital distribution requires >~1000 BHs within 0.1 pc of Sgr A*. A dissipationless formation scenario for the Milky Way NC is consistent with this lower limit and therefore could reconcile the need for high central densities of BHs (to explain the orbits of the S-stars), with the missing-cusp problem of the GC giant star population.

3 citations

Journal ArticleDOI
TL;DR: In this paper, the dynamical evolution of an isolated self-gravitating system with two stellar mass groups was studied, where the individual ratio of the heavy to light bodies was varied from 1.25 to 50 and the fraction of total heavy mass from 5% to 40% of the whole cluster mass.
Abstract: We address the dynamical evolution of an isolated self--gravitating system with two stellar mass groups. We vary the individual ratio of the heavy to light bodies, $\mu$ from 1.25 to 50 and alter also the fraction of the total heavy mass $\MH$ from 5% to 40% of the whole cluster mass. Clean-cut properties of the cluster dynamics are examined, like core collapse, the evolution of the central potential, as well as escapers. We present in this work collisional $N$-body simulations, using the high--order integrator NBODY6++ with up to ${\cal N}_{\star}=2\cdot 10^4$ particles improving the statistical significancy of the lower--${\cal N}_{\star}$ simulations by ensemble averages. Equipartition slows down the gravothermal contraction of the core slightly. Beyond a critical value of $\mu \approx 2$, no equipartition can be achieved between the different masses; the heavy component decouples and collapses. For the first time the critical boundary between Spitzer--stable and --unstable systems is demonstrated in direct $N$-body models.

3 citations

Journal ArticleDOI
TL;DR: In this article, a two-component family of truncated models is proposed to model the mass segregation and the presence of multiple populations of globular clusters, which can provide a more realistic description of the observed photometric and spectroscopic profiles.
Abstract: Recently, a class of non-truncated radially-anisotropic models (the so-called $f^{( u)}$-models), originally constructed in the context of violent relaxation and modeling of elliptical galaxies, has been found to possess interesting qualities in relation to observed and simulated globular clusters. In view of new applications to globular clusters, we improve this class of models along two directions. To make them more suitable for the description of small stellar systems hosted by galaxies, we introduce a 'tidal' truncation (by means of a procedure that guarantees full continuity of the distribution function). The new $f_T^{( u)}$-models are shown to provide a better fit to the observed photometric and spectroscopic profiles for a sample of 13 globular clusters studied earlier by means of non-truncated models; interestingly, the best-fit models also perform better with respect to the radial-orbit instability. Then we design a flexible but simple two-component family of truncated models, to study the separate issues of mass segregation and of multiple populations. We do not aim at a fully realistic description of globular clusters, to compete with the description currently obtained by means of dedicated simulations. The goal here is to try to identify the simplest models, that is, those with the smallest number of free parameters, but still able to provide a reasonable description for clusters that are evidently beyond the reach of one-component models: with this tool we aim at identifying the key factors that characterize mass segregation or the presence of multiple populations. To reduce the relevant parameter space, we formulate a few physical arguments (based on recent observations and simulations). A first application to two well-studied globular clusters is briefly described and discussed.

3 citations

M. Pasquato1
01 Jan 2009
TL;DR: In this paper, a method for fingerprinting the presence of intermediate mass black holes (IMBHs) in the cores of Globular Clusters (GCs) is presented.
Abstract: Intermediate Mass Black Holes (IMBHs; with mass in the 10 − 10 M range) may be present in the cores of Globular Clusters (GCs) While the existence of IMBHs would have implications for galactic formation and evolution and GC dynamics, there has been no definitive detection of such an object to date I present a new method for fingerprinting the presence of an IMBH which does not require information on the kinematics of GC stars and is applicable to collisionally relaxed GCs Via two-body interactions, heavy stars sink to the center of a GC over several relaxation times, while lighter stars move to the periphery and preferentially evaporate from the system N-body simulations show that the presence of an IMBH quenches such a mass segregation The new method is based on comparing the observed GC mass segregation profile with predictions from N-body simulations with and without an IMBH I compare a comprehensive set of such simulations to the mass segregation profile of NGC 2298 based on HST/ACS photometry and find that the presence of an IMBH greater than 300 solar masses can be rejected to the 3-σ level Simulations without an IMBH also correctly predict the present day mass function of NGC 2298

3 citations

Journal ArticleDOI
TL;DR: In this article, the dissolution process of young embedded star clusters with different primordial mass segregation levels using fractal distributions was investigated by means of N-body simulations, and it was shown that the fraction of bound stellar mass can be well predicted just right after the gas expulsion but tends to be lower at later stages, as these systems evolve due to the stronger two-body interactions resulting from the inclusion of a realistic initial mass function.
Abstract: We investigate the dissolution process of young embedded star clusters with different primordial mass segregation levels using fractal distributions by means of N-body simulations. We combine several star clusters in virial and subvirial global states with Plummer and uniform density profiles to mimic the gas. The star clusters have masses of M-stars = 500 M-circle dot that follow an initial mass function where the stars have maximum distance from the centre of r = 1.5 pc. The clusters are placed in clouds that at the same radius have masses of M-cloud = 2000 M-circle dot, resulting in star formation efficiency of 0.2. We remove the background potential instantaneously at a very early phase, mimicking the most destructive scenario of gas expulsion. The evolution of the fraction of bound stellar mass is followed for a total of 16 Myr for simulations with stellar evolution and without. We compare our results with previous works using equal-mass particles where an analytical physical model was used to estimate the bound mass fraction after gas expulsion. We find that independent of the initial condition, the fraction of bound stellar mass can be well predicted just right after the gas expulsion but tends to be lower at later stages, as these systems evolve due to the stronger two-body interactions resulting from the inclusion of a realistic initial mass function. This discrepancy is independent of the primordial mass segregation level.

3 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202336
202225
202133
202047
201943
201822