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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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Journal ArticleDOI
TL;DR: In this paper, the authors proposed a simple test for the existence of a cluster of black hole remnants around Sgr A* that is based on a small sample of any type of Galactic center objects, provided they are substantially less massive than the black holes and constitute part of an old population.
Abstract: We propose a simple test for the existence of a cluster of black hole remnants around Sgr A* that is based on a small sample of any type of Galactic center objects, provided they are substantially less massive than the black holes and constitute part of an old (1 Gyr) population. The test relies on the fact that, in the presence of such a cluster of heavy remnants and because of energy equipartition, lower mass objects would be expelled from the central regions and settle into a distribution very different from the cusp expected to be induced by the supermassive black hole alone. We show that with a sample of just 50 objects and using only their angular positions on the sky relative to Sgr A*, it is possible to clearly differentiate between a distribution consistent with the presence of the cluster of black holes and a power-law cusp distribution. We argue that millisecond pulsars might currently be the best candidate to perform this test, because of the large uncertainties involved in the age determination of less exotic objects. In addition, by measuring their first and second period derivatives, millisecond pulsars offer the rare opportunity to determine the complete phase-space information of the objects. We show that this extra information improves the detection of mass segregation by about 30%.

13 citations

Journal ArticleDOI
TL;DR: In this article, high-resolution spectra of 16 stars in the field of the young open cluster NGC 6913 were obtained to constrain its main properties and study its internal kinematics.
Abstract: Between 1996 and 2003 we have obtained 226 high resolution spectra of 16 stars in the field of the young open cluster NGC 6913, to the aim of constraining its main properties and study its internal kinematics. Twelve of the program stars turned out to be members, one of them probably unbound. Nine are binaries (one eclipsing and another double lined) and for seven of them the observations allowed to derive the orbital elements. All but two of the nine discovered binaries are cluster members. In spite of the young age (a few Myr), the cluster already shows signs that could be interpreted as evidence of dynamical relaxation and mass segregation. However, they may be also the result of an unconventional formation scenario. The dynamical (virial) mass as estimated from the radial velocity dispersion is larger than the cluster luminous mass, which may be explained by a combination of the optically thick interstellar cloud that occults part of the cluster, the unbound state or undetected very wide binary orbit of some of the members that inflate the velocity dispersion and a high inclination for the axis of a possible cluster angular momentum. All discovered binaries are hard enough to survive average close encounters within the cluster and do not yet show sign of relaxation of the orbital elements to values typical of field binaries.

12 citations

Journal ArticleDOI
TL;DR: In this paper, a detailed study of mass segregation in the globular cluster NGC6397 is presented, where the luminosity function shows a higher density of bright stars near the central region of the data with respect to the outer region.
Abstract: In this study, we present a detailed study of mass segregation in the globular cluster NGC6397. First, we carry out a photometric analysis of projected ESO-VLT data (between 1 and 10arcmin from the cluster centre), presenting the luminosity function corrected by completeness. The luminosity function shows a higher density of bright stars near the central region of the data, with respect to the outer region. We calculate a deprojected model (covering the whole cluster) estimating a total number of stars of 193000±19000. The shapes of the surface brightness and density-number profiles versus the radial coordinate r (instead of the projected coordinate R) lead to a decreasing luminosity for an average star, and thus of mass, up to 1arcmin, quantifying the mass segregation. The deprojected model does not show evidence of mass segregation outside this region.

12 citations

Journal ArticleDOI
TL;DR: In this article, the mass segregation in the core of globular clusters has been measured using direct N-body simulations with up to 200k particles, including stellar evolution, primordial binaries, and varying BH/neutron stars.
Abstract: The level of mass segregation in the core of globular clusters has been previously proposed as a potential indicator of the dynamical constituents of the system, such as presence of a significant population of stellar-mass black holes (BHs), or even a central intermediate-mass black hole (IMBH). However, its measurement is limited to clusters with high-quality Hubble Space Telescope data. Thanks to a set of state-of-the-art direct N-body simulations with up to 200k particles inclusive of stellar evolution, primordial binaries, and varying BH/neutron stars, we highlight for the first time the existence of a clear and tight linear relation between the degree of mass segregation and the cluster structural concentration index. The latter is defined as the ratio of the radii containing 5% and 50% of the integrated light ($R_5/R_\mathrm{50}$), making it robustly measurable without the need to individually resolve low-mass stars. Our simulations indicate that given $R_5/R_\mathrm{50}$, the mass segregation $\Delta m$ (defined as the difference in main sequence median mass between center and half-light radius) is expressed as $\Delta m/M_\odot = -1.166 R_5/R_\mathrm{h} + 0.3246$, with a root-mean-square error of $0.0148$. In addition, we can explain its physical origin and the values of the fitted parameters through basic analytical modeling. Such correlation is remarkably robust against a variety of initial conditions (including presence of primordial binaries and IMBHs) and cluster ages, with a slight dependence in best-fit parameters on the prescriptions used to measure the quantities involved. Therefore, this study highlights the potential to develop a new observational tool to gain insight on the dynamical status of globular clusters and on its dark remnants.

12 citations

Journal Article
TL;DR: In this article, N-body simulations of globular clusters, in orbits around the Galaxy, in order to study quantitatively and geometrically the tidal effects they encounter are presented.
Abstract: We present N-body simulations of globular clusters, in orbits around the Galaxy, in order to study quantitatively and geometrically the tidal effects they encounter. The clusters are modelised with multi-mass King-Michie models (Michie 1963), including mass segregation at initial conditions. The Galaxy is modelled as realistic as possible, with three components: bulge, disk and dark halo. The main finding is that there exist two giant tidal tails around the globuler cluster in permanence along its orbit, whatever this orbit. The length of these tails is of the order of 5 tidal radii, or greater. The escaped stars are dis- tributed radially as a power law in density, with a slope of -4. The tails present substructures, or clumps, that are the relics of the strongest shocks. Due to the compressive disk-shocking, the clusters display a prolate shape whose major axis is precessing around the z axis. The tails are preferentially formed by the low- est mass stars, as expected, so that the tidal truncation increases mass segregation. Internal rotation of the cluster increases the mass loss. The flattening of dark matter cannot influence sig- nificantly the dynamics of the clusters. The orientation and the strength of the tidal tails are signatures of the last disk cross- ing, so that observed tidal tails can constrain strongly the cluster orbit and the galactic model (vertical scale of the disc).

12 citations


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