On the presence of intermediate black holes in three globular clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 400-403
Author(s):  
Holger Baumgardt ◽  
Antonio Sollima ◽  
Michael Hilker
Keyword(s):  
Black Holes ◽  
Surface Density ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Initial Density ◽  
Mass Function ◽  
Initial Mass Function ◽  
Intermediate Mass ◽  
Initial Cluster ◽  
Large Grid

AbstractWe investigate whether the globular clusters 47 Tuc, ω Cen and NGC 6624 contain intermediate-mass black holes (IMBHs) by fitting a large grid of N-body simulations against their surface density and velocity dispersion profiles. In our simulations we vary the initial cluster size, the initial mass function and the initial density profile of the clusters as well as the mass fraction of a central intermediate-mass black hole. We find that the surface density and velocity dispersion profiles of all three clusters can be better reproduced by models that do not contain a central IMBH than by any of our IMBH models. If ω Cen and NGC 6624 contain any IMBHs at all, they have to be significantly less massive than suggested in the past.

scholarly journals No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624

2019 ◽  
Vol 488 (4) ◽  
pp. 5340-5351 ◽  
Author(s):  
H Baumgardt ◽  
C He ◽  
S M Sweet ◽  
M Drinkwater ◽  
A Sollima ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Velocity Dispersion ◽  
Stellar Mass ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Measured Velocity ◽  
Large Grid

ABSTRACT We compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters ω Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an $\sim 45\, 000$ M⊙ IMBH, whose presence has been suggested based on the measured velocity dispersion profile of ω Cen, predicts the existence of about 20 fast-moving, m > 0.5 M⊙, main-sequence stars with a (1D) velocity v > 60 km s−1 in the central 20 arcsec of ω Cen. However, no such star is present in the HST/ACS proper motion catalogue of Bellini et al. (2017), strongly ruling out the presence of a massive IMBH in the core of ω Cen. Instead, we find that all available data can be fitted by a model that contains 4.6 per cent of the mass of ω Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of N-body simulations with NGC 6624, a cluster recently claimed to harbour a 20 000 M⊙ black hole based on timing observations of millisecond pulsars. However, we find that models with MIMBH > 1000 M⊙ IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624, ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624.

scholarly journals Multiple Stellar Populations in Globular Clusters: Collection of Information from the Horizontal Branch

2007 ◽  
Vol 3 (S246) ◽  
pp. 156-160 ◽  
Author(s):  
Francesca D'Antona ◽  
Vittoria Caloi
Keyword(s):  
Globular Clusters ◽  
Second Generation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Rotating Stars ◽  
Initial Cluster ◽  
Stellar Component ◽  
Central Regions ◽  
Chemical Anomalies ◽  
The Many

AbstractThe majority of the inhomogeneities in the chemical composition of Globular Cluster (GC) stars appear due to primordial enrichment by hot-CNO cycled material processed in stars belonging to a first stellar generation. Either massive AGB envelopes subject to hot bottom burning, or the envelopes of massive fastly rotating stars could be the progenitors. In both cases, the stars showing chemical anomalies must have also enhanced helium abundance, and we have proposed that this higher helium could be at the basis of the many different morphologies of GC horizontal branches (HB) for similar ages and metallicities. The helium variations have been beautifully confirmed by the splitting of the main sequence in the clusters ω Cen and NGC 2808, but this effect can show up only for somewhat extreme helium abundances. Therefore it is important to go on using the HB morphology to infer the number ratio of the first to the second generation in as many clusters as possible. We exemplify how it is possible to infer the presence of a He – rich stellar component in different clusters thanks to different HB features (gaps, RR Lyr periods and period distribution, ratio of blue to red stars, blue tails). In many clusters at least 50% of the stars belong to the second stellar generation, and in some cases we suspect that the stars might all belong to the second generation. We shortly examine the problem of the initial mass function required to achieve the observed number ratios and conclude that: 1) the initial cluster must have been much more massive than today's cluster, and 2) formation of the second stellar generation mainly in the central regions of the cluster may help in obtaining the desired values.

scholarly journals Comparing IMF-sensitive indices of intermediate-mass quiescent galaxies in various environments

2019 ◽  
Vol 486 (3) ◽  
pp. 3788-3804 ◽  
Author(s):  
Elham Eftekhari ◽  
Moein Mosleh ◽  
Alexandre Vazdekis ◽  
Saeed Tavasoli
Keyword(s):  
Large Scale ◽  
Velocity Dispersion ◽  
Mass Function ◽  
Initial Mass Function ◽  
Sloan Digital Sky Survey ◽  
Intermediate Mass ◽  
Composite Spectra ◽  
Stellar Initial Mass Function ◽  
Varying Environments ◽  
The Imf

ABSTRACT Using samples drawn from the Sloan Digital Sky Survey, we study for the first time the relation between large-scale environments (clusters, groups, and voids) and the stellar initial mass function (IMF). We perform an observational approach based on the comparison of IMF-sensitive indices of quiescent galaxies with similar mass in varying environments. These galaxies are selected within a narrow redshift interval (0.020 < z < 0.055) and spanning a range in velocity dispersion from 100 to 200 km s−1. The results of this paper are based upon analysis of composite spectra created by stacking the spectra of galaxies, binned by their velocity dispersion and redshift. The trends of spectral indices as measured from the stacked spectra, with respect to velocity dispersion, are compared in different environments. We find a lack of dependence of the IMF on the environment for intermediate-mass galaxy regime. We verify this finding by providing a more quantitative measurement of the IMF variations among galactic environments using MILES stellar population models with a precision of ΔΓb ∼ 0.2.

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 Searching for intermediate mass black holes: understanding the data first

2014 ◽  
Vol 10 (S312) ◽  
pp. 223-226
Author(s):  
Paolo Bianchini ◽  
Mark Norris ◽  
Glenn van de Ven ◽  
Eva Schinnerer
Keyword(s):  
Black Holes ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Data Cube ◽  
Intermediate Mass ◽  
Integral Field Spectroscopy ◽  
Kinematic Measurement ◽  
Intrinsic Scatter ◽  
Integral Field ◽  
Intermediate Mass Black Holes

AbstractThe detection of intermediate mass black holes (IMBHs) in globular clusters has been hotly debated, with different observational methods delivering different outcomes for the same object. In order to understand these discrepancies, we construct detailed mock integral field spectroscopy (IFU) observations of globular clusters, starting from realistic Monte Carlo cluster simulations. The output is a data cube of spectra in a given field-of-view that can be analyzed in the same manner as real observations and compared to other (resolved) kinematic measurement methods. We show that the main discrepancies arise because the luminosity-weighted IFU observations can be strongly biased by the presence of a few bright stars that introduce a scatter in velocity dispersion measurements of several km s−1. We show that this intrinsic scatter can prevent a sound assessment of the central kinematics, and therefore should be fully taken into account to correctly interpret the signature of an IMBH.

scholarly journals Intermediate-Mass Black Holes

2020 ◽  
Vol 58 (1) ◽  
pp. 257-312 ◽  
Author(s):  
Jenny E. Greene ◽  
Jay Strader ◽  
Luis C. Ho
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Globular Clusters ◽  
High Redshift ◽  
Mass Function ◽  
Intermediate Mass ◽  
The Galaxy ◽  
Robust Measurements ◽  
Black Hole Masses ◽  
Intermediate Mass Black Holes

We describe ongoing searches for intermediate-mass black holes with MBH ≈ 10–105 M⊙. We review a range of search mechanisms, both dynamical and those that rely on accretion signatures. We find the following conclusions: ▪  Dynamical and accretion signatures alike point to a high fraction of 109–1010 M⊙ galaxies hosting black holes with MBH∼ 105 M⊙. In contrast, there are no solid detections of black holes in globular clusters. ▪  There are few observational constraints on black holes in any environment with MBH ≈ 100–104 M⊙. ▪  Considering low-mass galaxies with dynamical black hole masses and constraining limits, we find that the MBH–σ* relation continues unbroken to MBH ∼105 M⊙, albeit with large scatter. We believe the scatter is at least partially driven by a broad range in black hole masses, because the occupation fraction appears to be relatively high in these galaxies. ▪  We fold the observed scaling relations with our empirical limits on occupation fraction and the galaxy mass function to put observational bounds on the black hole mass function in galaxy nuclei. ▪  We are pessimistic that local demographic observations of galaxy nuclei alone could constrain seeding mechanisms, although either high-redshift luminosity functions or robust measurements of off-nuclear black holes could begin to discriminate models.

scholarly journals Hunting for intermediate-mass black holes in globular clusters: an astrometric study of NGC 6441

2021 ◽  
Vol 503 (1) ◽  
pp. 1490-1506
Author(s):  
Maximilian Häberle ◽  
Mattia Libralato ◽  
Andrea Bellini ◽  
Laura L Watkins ◽  
Jörg-Uwe Pott ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Velocity Dispersion ◽  
Angular Resolution ◽  
Hubble Space Telescope ◽  
High Mass ◽  
High Angular Resolution ◽  
Stellar Kinematics ◽  
Intermediate Mass ◽  
The Core ◽  
Large Telescopes

ABSTRACT We present an astrometric study of the proper motions (PMs) in the core of the globular cluster NGC 6441. The core of this cluster has a high density and observations with current instrumentation are very challenging. We combine ground-based, high-angular-resolution NACO@VLT images with Hubble Space Telescope ACS/HRC data and measure PMs with a temporal baseline of 15 yr for about 1400 stars in the centremost 15 arcsec of the cluster. We reach a PM precision of ∼30 µas yr−1 for bright, well-measured stars. Our results for the velocity dispersion are in good agreement with other studies and extend already existing analyses of the stellar kinematics of NGC 6441 to its centremost region never probed before. In the innermost arcsecond of the cluster, we measure a velocity dispersion of (19.1 ± 2.0) km s−1 for evolved stars. Because of its high mass, NGC 6441 is a promising candidate for harbouring an intermediate-mass black hole (IMBH). We combine our measurements with additional data from the literature and compute dynamical models of the cluster. We find an upper limit of $M_{\rm IMBH} \lt 1.32 \times 10^4\, \textrm{M}_\odot$ but we can neither confirm nor rule out its presence. We also refine the dynamical distance of the cluster to $12.74^{+0.16}_{-0.15}$ kpc. Although the hunt for an IMBH in NGC 6441 is not yet concluded, our results show how future observations with extremely large telescopes will benefit from the long temporal baseline offered by existing high-angular-resolution data.

scholarly journals Intermediate-mass black holes in globular clusters: observations and simulations - Update

2015 ◽  
Vol 12 (S316) ◽  
pp. 240-245
Author(s):  
Nora Lützgendorf ◽  
Markus Kissler-Patig ◽  
Karl Gebhardt ◽  
Holger Baumgardt ◽  
Diederik Kruijssen ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Globular Clusters ◽  
Galactic Center ◽  
Early Stage ◽  
Life Time ◽  
Intermediate Mass ◽  
Software Environment ◽  
Integral Field ◽  
Intermediate Mass Black Holes

AbstractThe study of intermediate-mass black holes (IMBHs) is a young and promising field of research. If IMBH exist, they could explain the rapid growth of supermassive black holes by acting as seeds in the early stage of galaxy formation. Formed by runaway collisions of massive stars in young and dense stellar clusters, intermediate-mass black holes could still be present in the centers of globular clusters, today. We measured the inner kinematic profiles with integral-field spectroscopy for 10 Galactic globular cluster and determined masses or upper limits of central black holes. In combination with literature data we further studied the positions of our results on known black-hole scaling relations (such as M• − σ) and found a similar but flatter correlation for IMBHs. Applying cluster evolution codes, the change in the slope could be explained with the stellar mass loss occurring in clusters in a tidal field over its life time. Furthermore, we present results from several numerical simulations on the topic of IMBHs and integral field units (IFUs). N-body simulations were used to simulate IFU data cubes. For the specific case of NGC 6388 we simulated two different IFU techniques and found that velocity dispersion measurements from individual velocities are strongly biased towards lower values due to blends of neighbouring stars and background light. In addition, we use the Astrophysical Multipurpose Software Environment (AMUSE) to combine gravitational physics, stellar evolution and hydrodynamics to simulate the accretion of stellar winds onto a black hole. We find that the S-stars need to provide very strong winds in order to explain the accretion rate in the galactic center.

scholarly journals Statistical Properties of Kerr BH Flywheel Model of QSOs/AGNs

2000 ◽  
Vol 195 ◽  
pp. 417-418
Author(s):  
S. Nitta
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Kerr Black Hole ◽  
Mass Function ◽  
Initial Mass Function ◽  
Number Density ◽  
Disk System ◽  
The Press ◽  
The Individual ◽  
Density Population

The aim of this work is to demonstrate the properties of the magnetospheric model around Kerr black holes, so-called the “flywheel” (rotation powered) model. The fly-wheel engine of the BH accretion disk system is applied to the statistics of QSOs/AGNs. Nitta, Takahashi, & Tomimatsu clarified the individual evolution of the Kerr black-hole fly-wheel engine, which is parameterized by black-hole mass, initial Kerr parameter, magnetic field near the horizon, and a dimensionless small parameter. We impose a statistical model for the initial mass function of an ensemble of black holes using the Press-Schechter formalism. With the help of additional assumptions, we can discuss the evolution of the luminosity function and the spatial number density (population) of QSOs/AGNs. The result explains well the decrease of very bright QSOs and decrease of population after z ~ 2.

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