Hypervelocity stars from star clusters hosting intermediate-mass black holes

ABSTRACT Hypervelocity stars (HVSs) represent a unique population of stars in the Galaxy reflecting properties of the whole Galactic potential. Determining their origin is of fundamental importance to constrain the shape and mass of the dark halo. The leading scenario for the ejection of HVSs is an encounter with the supermassive black hole in the Galactic centre. However, new proper motions from the Gaia mission indicate that only the fastest HVSs can be traced back to the Galactic centre and the remaining stars originate in the disc or halo. In this paper, we study HVSs generated by encounters of stellar binaries with an intermediate-mass black hole (IMBH) in the core of a star cluster. For the first time, we model the effect of the cluster orbit in the Galactic potential on the observable properties of the ejected population. HVSs generated by this mechanism do not travel on radial orbits consistent with a Galactic centre origin, but rather point back to their parent cluster, thus providing observational evidence for the presence of an IMBH. We also model the ejection of high-velocity stars from the Galactic population of globular clusters, assuming that they all contain an IMBH, including the effects of the cluster’s orbit and propagation of the star in the Galactic potential up to detection. We find that high-velocity stars ejected by IMBHs have distinctive distributions in velocity, Galactocentric distance and Galactic latitude, which can be used to distinguish them from runaway stars and stars ejected from the Galactic Centre.

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A numerical study of Galactic Centre stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3797 ◽

2020 ◽

Vol 501 (2) ◽

pp. 2418-2423

Author(s):

Oscar Salcido ◽

Carlos Calcaneo-Roldan

Keyword(s):

Black Hole ◽

Numerical Study ◽

Semimajor Axis ◽

Galactic Centre ◽

Central Black Hole ◽

Central Object ◽

Galactic Potential ◽

The Galaxy ◽

Inner Parts ◽

Strong Agreement

ABSTRACT We present a simulation of the orbits of Galactic Centre stars, also known as ‘S-stars’, with the purpose of describing the motion of those bodies for which complete orbits are known with greater accuracy. The aim is to have a better understanding of the inner parts of the Galactic potential. The simulation assumes that the spacetime around the central black hole of the Galaxy may be modelled by the Schwarzschild metric, while stellar interactions are approximated classically. We model the central object as a black hole with mass 4.31 × 106 M⊙, fix the Galactic Centre distance at R = 8.33 kpc and include 37 orbiting stars, all of which have masses of 10 M⊙, except for S2, which has a mass of 20 M⊙. Our method allows us to predict the semimajor axis, a; eccentricity, ϵ; and period, T for these stars and predict their periastron shift, δΘ. In particular for S2, the most scrutinized star, we find δΘ = 11.9342 arcmin, in strong agreement with the observed value.

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Scattering of Pulsar Radiation and Electron Density Turbulence in the Interstellar Medium

Australian Journal of Physics ◽

10.1071/ph860433 ◽

1986 ◽

Vol 39 (3) ◽

pp. 433 ◽

Cited By ~ 19

Author(s):

SK Alurkar ◽

OB Slee ◽

AD Bobra

Keyword(s):

Electron Density ◽

Heliocentric Distance ◽

Galactic Centre ◽

Published Data ◽

Dispersion Measure ◽

Galactic Latitude ◽

Galactocentric Distance ◽

Pulsar Radiation ◽

The Galaxy ◽

Average Electron

We report measurements, using the Culgoora circular array at 80 and 160 MHz and the Parkes 64 m telescope at 410 MHz, of the pulse broadening due to interstellar scattering on 33 pulsars. These results are added to published data on 52 other pulsars in order to investigate the interstellar turbulence levels over 85 paths in the Galaxy. We find a significant relation between the turbulence level C~ and dispersion measure, heliocentric distance, galactocentric distance, galactic latitude and galactic longitude. Our results are consistent with a distribution of turbulence that peaks near the galactic centre and extends out to past the solar circle, with the scale height perpendicular to the plane at least equal to that of the pulsars. The magnitude of the fluctuations in electron density responsible for the scattering is not proportional to the average electron density, but increases much more rapidly than the latter as the galactic centre is approached. The apparent dependence of C~ on heliocentric distance is preferentially interpreted as due to the presence of a highly clumped distribution of turbulence along all lines of sight.

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Intermediate-Mass Black Holes

Annual Review of Astronomy and Astrophysics ◽

10.1146/annurev-astro-032620-021835 ◽

2020 ◽

Vol 58 (1) ◽

pp. 257-312 ◽

Cited By ~ 7

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.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315010601 ◽

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.

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Gravitational Waves and Intermediate-mass Black Hole Retention in Globular Clusters

The Astrophysical Journal ◽

10.3847/1538-4357/aab368 ◽

2018 ◽

Vol 856 (2) ◽

pp. 92 ◽

Cited By ~ 47

Author(s):

Giacomo Fragione ◽

Idan Ginsburg ◽

Bence Kocsis

Keyword(s):

Black Hole ◽

Gravitational Waves ◽

Globular Clusters ◽

Intermediate Mass

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2060 ◽

2019 ◽

Vol 488 (4) ◽

pp. 5340-5351 ◽

Cited By ~ 16

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.

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An Upper Limit to the Mass Loss from the Centre of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900235948 ◽

1974 ◽

Vol 64 ◽

pp. 36-36

Author(s):

Arcadio Poveda ◽

Christine Allen

Keyword(s):

Mass Loss ◽

Gravitational Waves ◽

Mass Distribution ◽

Globular Clusters ◽

Loss Rate ◽

Galactic Centre ◽

Isotropic Source ◽

The Past ◽

Upper Limit ◽

The Galaxy

A mass loss of 200 M⊙ per year, as conservatively suggested if Weber is detecting gravitational waves from an isotropic source at the galactic centre, is shown to be incompatible with the existence of (a) globular clusters, (b) old wide binaries, if this loss rate has been constant over the past 1010 yr.From the orbit of ω Centauri in the galactic field and its observed mass distribution and tidal radius an upper limit to the mass loss from the galactic centre is found to be 1 M⊙ yr-1 over the past 1010 yr.

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The Chemical Abundances of the Halo Clusters of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900145504 ◽

1978 ◽

Vol 80 ◽

pp. 177-182

Author(s):

R. Canterna ◽

R. A. Schommer

Keyword(s):

Globular Clusters ◽

Broad Band ◽

Mean Value ◽

Red Giants ◽

Galactocentric Distance ◽

Chemical Abundances ◽

Dwarf Spheroidal Galaxies ◽

The Galaxy ◽

Ursa Minor ◽

Metal Abundances

Photometric metal abundances of individual red giants in eight extremely distant halo globular clusters and the Draco and Ursa Minor dwarf spheroidal galaxies have been obtained using the Washington broad-band system, C, M, T1, T2(Canterna 1976). Observations were made at the KPNO 2.1-m and CTIO 1.5-m telescopes. In Table I we list for each system the mean value of [Fe/H], the number of stars observed in each system, n, the Galactocentric distance, RGC, the intrinsic color of the giant branch at the level of the horizontal branch (HB), (B-V)o,g, and the fraction of HB stars bluer than the RR Lyrae gap, fB. Sources for unpublished color-magnitude diagram (CMD) data are: Pal 11 (Canterna and Schommer), Pal 12 (Canterna and Harris), and Ursa Minor (Schommer, Olszewski and Kunkel).

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The Gas-to-Dust Ratio in the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900026401 ◽

1974 ◽

Vol 60 ◽

pp. 179-182

Author(s):

F. J. Kerr ◽

G. R. Knapp

Keyword(s):

Globular Clusters ◽

Galactic Latitude ◽

Interstellar Clouds ◽

The Galaxy ◽

Intercloud Medium

We have investigated the gas-to-dust ratio in the Galaxy by comparing 21-cm Hicolumn densities with the color excesses of globular clusters. We find a constant gas-to-reddening ratio in interstellar clouds and the intercloud medium. This ratio is also independent of galactic latitude.

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