scholarly journals Stellar-mass black holes in star clusters: implications for gravitational-wave radiation

2009 ◽  
Vol 5 (S266) ◽  
pp. 213-218
Author(s):  
Sambaran Banerjee ◽  
Holger Baumgardt ◽  
Pavel Kroupa
Keyword(s):  
Black Holes ◽  
Star Clusters ◽  
Stellar Mass ◽  
Wave Radiation ◽  
Initial Population ◽  
Low Mass Stars ◽  
Low Mass ◽  
Three Body ◽  
Massive Clusters ◽  
Hubble Time

AbstractWe study the dynamics of stellar-mass black holes (BHs) in star clusters, with particular attention to the formation of BH–BH binaries, which are interesting as sources of gravitational waves (GWs). We examine the properties of these BH–BH binaries through direct N-body simulations of Plummer clusters of N ≤ 105 low-mass stars with an initial population of stellar-mass BHs, using the nbody6 code. We find that the stellar-mass BHs segregate rapidly into the cluster core and form a dense subcluster of BHs in which BH–BH binaries form through three-body encounters. While most BH binaries are ejected from the cluster by recoils due to superelastic encounters with the single BHs, we find that for clusters with N ≳ 5 × 104, typically a few of them harden sufficiently so that they can merge via GW emission within the cluster. Also, for each of such clusters there are a few escaping BH binaries that merge within a Hubble time, with most merger times being within a few Gyr. These results imply that the intermediate-age massive clusters constitute the most important class of star cluster candidates that can produce dynamical BH–BH mergers at the present epoch. The BH–BH merger rates obtained from our computations imply a significant detection rate (~30 yr−1) for the proposed Advanced LIGO GW detector.

scholarly journals Ages of Galactic and Extragalactic Star Clusters of Various Abundances

1983 ◽  
Vol 6 ◽  
pp. 109-117 ◽  
Author(s):  
R.D. Cannon
Keyword(s):  
Star Clusters ◽  
Magellanic Clouds ◽  
Open Clusters ◽  
Simultaneous Solution ◽  
Low Mass Stars ◽  
Cluster Systems ◽  
Distant Cluster ◽  
Low Mass

In this review I shall concentrate mainly on globular star clusters in our Galaxy since these are the objects for which most work has been done recently, both observationally and theoretically. However, I shall also discuss briefly the oldest open clusters and clusters in the Magellanic Clouds. Little can be said about more distant cluster systems, since the only observations available are of integrated colours or spectra and these seem to be rather unreliable indicators of age. It is perhaps worth pointing out that the title may be slightly misleading; the problem is not so much to determine the ages of clusters of known abundances, as to obtain the best simultaneous solution for both age and composition, since some of the most important abundances (notably helium and oxygen) are virtually unobservable in little-evolved low mass stars.

scholarly journals Observations of low mass stars in clusters: Some constraints and puzzles for stellar evolution theory

1984 ◽  
Vol 105 ◽  
pp. 123-138
Author(s):  
R.D. Cannon
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Clusters ◽  
Variable Stars ◽  
Open Clusters ◽  
Low Mass Stars ◽  
Theory Of Evolution ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Red Giant

This review will attempt to do two things: (i) discuss some of the data which are available for testing the theory of evolution of low mass stars, and (ii) point out some problem areas where observations and theory do not seem to agree very well. This is of course too vast a field of research to be covered in one brief review, so I shall concentrate on one particular aspect, namely the study of star clusters and especially their colour-magnitude (CM) diagrams. Star clusters provide large samples of stars at the same distance and with the same age, and the CM diagram gives the easiest way of comparing theoretical predictions with observations, although crucial evidence is also provided by spectroscopic abundance analyses and studies of variable stars. Since this is primarily a review of observational data it is natural to divide it into two parts: (i) galactic globular clusters, and (ii) old and intermediate-age open clusters. Some additional evidence comes from Local Group galaxies, especially now that CM diagrams which reach the old main sequence are becoming available. For each class of cluster I shall consider successive stages of evolution from the main sequence, up the hydrogen-burning red giant branch, and through the helium-burning giant phase.

scholarly journals Stellar-mass Black Holes in Globular Clusters: Dynamical consequences and observational signatures

2019 ◽  
Vol 14 (S351) ◽  
pp. 395-399 ◽  
Author(s):  
Abbas Askar ◽  
Mirek Giersz ◽  
Manuel Arca Sedda ◽  
Ammar Askar ◽  
Mario Pasquato ◽  
...  
Keyword(s):  
Black Holes ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Stellar Mass ◽  
Large Set ◽  
Term Survival ◽  
Central Surface ◽  
Sizeable Number ◽  
Hubble Time

AbstractSizeable number of stellar-mass black holes (BHs) in globular clusters (GCs) can strongly influence the dynamical evolution and observational properties of their host cluster. Using results from a large set of numerical simulations, we identify the key ingredients needed to sustain a sizeable population of BHs in GCs up to a Hubble time. We find that while BH natal kick prescriptions are essential in determining the initial retention fraction of BHs in GCs, the long-term survival of BHs is determined by the size, initial central density and half-mass relaxation time of the GC. Simulated GC models that contain many BHs are characterized by relatively low central surface brightness, large half-light and core radii values. We also discuss novel ways to compare simulated results with available observational data to identify GCs that are most likely to contain many BHs.

scholarly journals Young and intermediate-age massive star clusters

2010 ◽  
Vol 368 (1913) ◽  
pp. 867-887 ◽  
Author(s):  
Søren S. Larsen
Keyword(s):  
Star Formation ◽  
Star Clusters ◽  
Mass Function ◽  
Starburst Galaxies ◽  
Open Clusters ◽  
High Mass ◽  
Current Evidence ◽  
Power Law Distribution ◽  
Low Mass ◽  
Massive Clusters

An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>10 5  M ⊙ ) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, , but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M >2×10 5  M ⊙ . In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several ×10 6  M ⊙ . The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.

scholarly journals Young and old massive star clusters and their stellar populations - Theoretical challenges for the next decade

2015 ◽  
Vol 12 (S316) ◽  
pp. 1-8
Author(s):  
Corinne Charbonnel
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Local Group ◽  
Stellar Populations ◽  
Low Mass Stars ◽  
Open Questions ◽  
Low Mass ◽  
Near Future ◽  
Massive Clusters ◽  
Two Populations

AbstractSeveral models presented in the literature compete to explain the origin of multiple stellar populations in globular clusters (GC), but they all fail to reproduce the large variety of present-day characteristics of these systems. In parallel, independent clues on GC early evolution may be derived from observations of young massive clusters (YMC) in the Local Group. But are these two populations of clusters related? And can we reconcile the informations and data concerning GCs and YMCs? Here we summarize some open questions on the nucleosynthetic origin of multiple stellar populations in GCs, on the actual evolution and characteristics of GC low-mass stars, and on early gas expulsion from massive clusters. We propose theoretical paths to be explored in the near future.

scholarly journals Ejection of close-in super-Earths around low-mass stars in the giant impact stage

2020 ◽  
Vol 642 ◽  
pp. A23
Author(s):  
Yuji Matsumoto ◽  
Pin-Gao Gu ◽  
Eiichiro Kokubo ◽  
Shoichi Oshino ◽  
Masashi Omiya
Keyword(s):  
Surface Density ◽  
Dynamical Evolution ◽  
Central Star ◽  
Stellar Mass ◽  
Mass Relation ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Giant Impact ◽  
Low Mass ◽  
Strong Scattering

Context. Earth-sized planets were observed in close-in orbits around M dwarfs. While more and more planets are expected to be uncovered around M dwarfs, theories of their formation and dynamical evolution are still in their infancy. Aims. We investigate the giant impact stage for the growth of protoplanets, which includes strong scattering around low-mass stars. The aim is to clarify whether strong scattering around low-mass stars affects the orbital and mass distributions of the planets. Methods. We performed an N-body simulation of protoplanets by systematically surveying the parameter space of the stellar mass and surface density of protoplanets. Results. We find that protoplanets are often ejected after twice or three times the close-scattering around late M dwarfs. The ejection sets the upper limit of the largest planet mass. By adopting the surface density that linearly scales with the stellar mass, we find that as the stellar mass decreases, less massive planets are formed in orbits with higher eccentricities and inclinations. Under this scaling, we also find that a few close-in protoplanets are generally ejected. Conclusions. The ejection of protoplanets plays an important role in the mass distribution of super-Earths around late M dwarfs. The mass relation of observed close-in super-Earths and their central star mass is reproduced well by ejection.

scholarly journals Dynamics of Galactic Nuclei Containing Massive Remnant Stars

1996 ◽  
Vol 174 ◽  
pp. 293-302
Author(s):  
H. M. Lee
Keyword(s):  
Stellar System ◽  
Dynamical Evolution ◽  
Galactic Nuclei ◽  
Low Mass Stars ◽  
Stellar Component ◽  
Long Time ◽  
Low Mass ◽  
Relaxation Time Scale ◽  
Three Body ◽  
Compact Cluster

We have examined the dynamical evolution of stellar system containing massive remnant stellar component. If individual mass of remnant stars is much heavier than that of normal stars which comprise most of the mass in the cluster, remnant stars quickly form a subsystem within the core of cluster of ordinary stars. The subsystem evolves on its own relaxation time scale which is very short. However, the post collapse expansion driven by the three-body binary heating becomes very slow because the expansion energy of the compact subcluster can be easily absorbed by surrounding cluster. The gravitational radiation can lead to the merger of binaries when binaries become very hard. A central seed black hole might form if repeated merger becomes very efficient. Otherwise, relatively stable two-component phase of central compact cluster of remnant stars surrounded by larger cluster of low mass stars would last for a long time.

Unexpectedly high formation rate of merging binary black holes in open clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 204-207
Author(s):  
Jun Kumamoto ◽  
Michiko S. Fujii ◽  
Ataru Tanikawa
Keyword(s):  
Black Holes ◽  
Globular Clusters ◽  
Formation Rate ◽  
Mass Function ◽  
Open Clusters ◽  
Binary Black Holes ◽  
Initial Cluster ◽  
Three Body ◽  
The Universe ◽  
Hubble Time

AbstractGravitational wave direct detections suggest that 30 M⊙ binary black holes (BBHs) commonly exist in the universe. One possible formation scenario of such BBHs is dynamical three-body encounters in dense star clusters. We performed a series of direct N-body simulations with a mass of 2500 and 10000 M⊙ and found a new channel for the formation of BBHs which is dominant in open clusters. In open clusters, the core-collapse time is shorter than in globular clusters, and therefore massive main-sequence (MS) binaries can form before they evolve to BHs. These MS binaries experience common envelope evolution and evolve to hard BBHs, which can merge within the Hubble time. The number of BBH mergers per unit mass obtained from our simulations reached 20–50 % of that for globular clusters, assuming an initial cluster mass function. Thus, open clusters can be a dominant formation site of hard BBHs.

scholarly journals MERGERS OF STELLAR-MASS BLACK HOLES IN NUCLEAR STAR CLUSTERS

2009 ◽  
Vol 692 (1) ◽  
pp. 917-923 ◽  
Author(s):  
M. Coleman Miller ◽  
Vanessa M. Lauburg
Keyword(s):  
Black Holes ◽  
Star Clusters ◽  
Stellar Mass
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