Stellar Remnants in Galactic Nuclei: Mass Segregation

Freitag, Marc; Amaro-Seoane, Pau; Kalogera, V.

doi:10.1086/506193

Cited by 250 publications

(389 citation statements)

References 168 publications

(262 reference statements)

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“…Hopman & Alexander (2006b) used Fokker-planck calculations to show that γ should be 1.4 for solar mass MS stars and up to 2 for stellar black holes (SBH). Similar results from MonteCarlo calculations were found by Freitag et al (2006) However, observations of red-giants in the Galactic center suggest a core-like structure in the inner regions of the GC (γ in the range 0 − 0.5; Do et al 2009;Bartko et al 2010;Genzel et al 2010. Nevertheless, it is not yet clear whether the distribution of red-giants reflect the overall distribution of stars in the GC, and various models had been suggested to explain both a "real" core distribution (Merritt 2010) or an apparent one (i.e., only reflecting the distribution of red-giants; Dale et al 2009;Amaro-Seoane & Chen 2014;Aharon & Perets 2015).…”

Section: Cusp and Core Models For The Nuclear Clustersupporting

confidence: 76%

Short- and long-term evolution of a stellar disc around a massive black hole: the role of the cusp, stellar evolution and binaries

Mikhaloff¹,

Perets²

2016

Mon. Not. R. Astron. Soc.

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We study the dynamical evolution of a stellar disk orbiting a massive black hole. We explore the role of two-body relaxation, mass segregation, stellar evolution and binary heating in affecting the disk evolution, and consider the impact of the nuclear cluster structure and the stellar-disk mass-function. We use analytic arguments and numerical calculations, and apply them to study the evolution of a stellar disk (similar to that observed in the Galactic center; GC), both on the short (few Myr) and longer (100 Myr) evolutionary timescales. We find the dominant processes affecting the disk evolution are two-body relaxation and mass segregation where as binary heating have only a little contribution. Massive stars play a dominant role in kinematically heating low mass stars, and driving them to high eccentricities/inclinations. Multi-mass models with realistic mass-functions for the disk stars show the disk structure to be mass stratified, with the most massive stars residing in thinner structures. Stellar evolution plays an important role in decreasing the number of massive stars with time, thereby leading to slower relaxation, where the remnant compact objects of these stars are excited to higher eccentricities/inclinations. At these later evolutionary stages dynamical heating by the nuclear cluster plays a progressively more important role. We conclude that the high eccentricities and high inclination observed for the majority on the young O-stars in the Galactic Center suggest that the disk stars had been formed with initially high eccentricities, or that collective or secular processes (not explored here) dominate the disk evolution. The latter processes are less likely to produce mass stratification in the disk; detailed study of the mass-dependent kinematic properties of the disk stars could therefore provide a handle on the processes that dominate its evolution. Finally, we find that the disk structure is expected to keep its coherency, and be observed as a relatively thin disk even after 100 Myrs; two-body relaxation is too inefficient for the disk to assimilate into the nuclear cluster on such timescales. It therefore suggests earlier disks now containing only older, lower mass stars might still be observed in the Galactic center, unless destroyed/smeared by other non-two-body relaxation processes.

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Section: Cusp and Core Models For The Nuclear Clustersupporting

confidence: 76%

Short- and long-term evolution of a stellar disc around a massive black hole: the role of the cusp, stellar evolution and binaries

Mikhaloff¹,

Perets²

2016

Mon. Not. R. Astron. Soc.

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“…S0-38 does improve the limit compared to S0-2 alone, but the main reason for the lower limit compared to earlier work is due to increased time coverage of the orbit of S0-2. Our new limit is still over an order of magnitude more than the ∼500-1000 M e of stellar remnants predicted to be within 0.01 pc (e.g., Freitag et al 2006), and other models predict even less mass within 0.01 pc (Merritt 2010). As observations of the orbits of S0-2 and S0-38 continue, the limits on the extended dark mass within 0.01 pc will continue to decrease.…”

Section: Scientific Implications Of New Constraints On M Bh and R Omentioning

confidence: 54%

“…In addition to the central SMBH, a central cluster of stellar-mass BHs and/or other compact objects has been predicted and theoretically explored (e.g., Morris 1993;Miralda-Escudé & Gould 2000;Freitag et al 2006;Merritt 2010). The amount of extended dark mass within the orbits of S0-2 and S0-38 influences their orbital motion.…”

Section: Values Derived From the Simultaneous Orbital Fit Of S0-38 Anmentioning

confidence: 99%

An Improved Distance and Mass Estimate for SGR A* From a Multistar Orbit Analysis

Boehle

Ghez

Schödel

et al. 2016

ApJ

349

413

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We present new, more precise measurements of the mass and distance of our Galaxy's central supermassive black hole, Sgr A * . These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A * , combining 2decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star's orbit from the deep adaptive optics data (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) to inform the search for the star in the speckle years (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005). When this new analysis technique is combined with the first complete re-reduction of Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 (K-band magnitude=17, orbital period=19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass (M bh ) and distance (R o ) of Sgr A * : M bh = (4.02±0.16±0.04) ×10 6 M e and 7.86±0.14±0.04 kpc. The uncertainties in M bh and R o as determined by the combined orbital fit of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of S0-2 alone and a factor of ∼2.5 compared to previous results from stellar orbits. This analysis also limits the extended dark mass within 0.01 pc to less than 0.13×10 6 M e at 99.7% confidence, a factor of 3 lower compared to prior work.

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“…This leads to the shallow density distribution of 1.5 (Bahcall & Wolf 1977). Later numerical simulations and analytical models confirmed these results (Freitag et al 2006;Preto & AmaroSeoane 2010;Hopman & Alexander 2006b). These steep density distributions were expected for the central cluster considering its age, which is comparable to the estimates of the two-body relaxation-time of 1−20 Gyr for the central parsec (Alexander 2005;Merritt 2010;Kocsis & Tremaine 2011).…”

Section: Introductionmentioning

confidence: 62%

“…Their volume density will be significantly reduced and they may even be expelled from the very center. Freitag et al (2006) show that the main-sequence stars begin to be expelled outward by the cusp of stellar-mass black holes (SBH) after a few Gyrs, just shorter than the presumed age of the stellar cluster at about 10 Gyr. While the reservoir of lower mass stars may be replenished by the most recent -possibly still ongoing -star formation episode about 6 million years ago (Paumard et al 2006), we assume that stars well below our low mass limit of ∼0.34 M with K s -band brightnesses around K s = 25 are affected by depletion.…”

Section: Extrapolating the Klf Of The S-star Clustermentioning

confidence: 99%

The S-star cluster at the center of the Milky Way

Sabha¹,

Eckart²,

Merritt³

et al. 2012

A&A

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Sagittarius A*, the super-massive black hole at the center of the Milky Way, is surrounded by a small cluster of high velocity stars, known as the S-stars. We aim to constrain the amount and nature of stellar and dark mass associated with the cluster in the immediate vicinity of Sagittarius A*. We use near-infrared imaging to determine the K s -band luminosity function of the S-star cluster members, and the distribution of the diffuse background emission and the stellar number density counts around the central black hole. This allows us to determine the stellar light and mass contribution expected from the faint members of the cluster. We then use post-Newtonian N-body techniques to investigate the effect of stellar perturbations on the motion of S2, as a means of detecting the number and masses of the perturbers. We find that the stellar mass derived from the K s -band luminosity extrapolation is much smaller than the amount of mass that might be present considering the uncertainties in the orbital motion of the star S2. Also the amount of light from the fainter S-cluster members is below the amount of residual light at the position of the S-star cluster after removing the bright cluster members. If the distribution of stars and stellar remnants is strongly enough peaked near Sagittarius A*, observed changes in the orbital elements of S2 can be used to constrain both their masses and numbers. Based on simulations of the cluster of high velocity stars we find that at a wavelength of 2.2 μm close to the confusion level for 8 m class telescopes blend stars will occur (preferentially near the position of Sagittarius A*) that last for typically 3 years before they dissolve due to proper motions.

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Stellar Remnants in Galactic Nuclei: Mass Segregation

Cited by 250 publications

References 168 publications

Short- and long-term evolution of a stellar disc around a massive black hole: the role of the cusp, stellar evolution and binaries

Short- and long-term evolution of a stellar disc around a massive black hole: the role of the cusp, stellar evolution and binaries

An Improved Distance and Mass Estimate for SGR A* From a Multistar Orbit Analysis

The S-star cluster at the center of the Milky Way

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