The Stellar Cusp around the Supermassive Black Hole in the Galactic Center

By R. Genzel, R. Schoedel, T. Ott, F. Eisenhauer, R. Hofmann, M. Lehnert, A. Eckart, T. Alexander, A. Sternberg, R. Lenzen and 5 more. 2003

483 citations recorded by the source corpus.

We analyze deep near-IR adaptive optics imaging (taken with NAOS/CONICA on the Very Large Telescope at the European Southern Observatory, Chile), as well as new proper-motion data of the nuclear star cluster of the Milky Way. The surface density distribution of faint (H ≤ 20, Ks ≤ 19) stars peaks within 0.″2 of the black hole candidate Sgr A*. The radial density distribution of this stellar "cusp" follows a power law of exponent α ~ 1.3-1.4. The K-band luminosity function of the overall nuclear stellar cluster (within 9′′ of Sgr A*) resembles that of the large-scale Galactic bulge but shows an excess of stars at Ks≤ 14. It fits population synthesis models of an old, metal-rich stellar population with a contribution from young, early, and late-type stars at the bright end. In contrast, the cusp within ≤1.″5 of Sgr A* appears to have a featureless luminosity function, suggesting that old, low-mass, horizontal-branch/red-clump stars are lacking. Likewise, there appear to be fewer late-type giants. The innermost cusp also contains a group of moderately bright, early-type stars that are tightly bound to the black hole. We interpret these results as evidence that the stellar properties change significantly from the outer cluster (≥a few arcseconds) to the dense innermost region around the black hole. We find that most of the massive early-type stars at distances of 1''-10'' from Sgr A* are located in two rotating and geometrically thin disks. These disks are inclined at large angles and counterrotate with respect to each other. Their stellar content is essentially the same, indicating that they formed at the same time. We conclude that of the possible formation scenarios for these massive stars the most probable one is that 5-8 million years ago two clouds fell into the center, collided, were shock compressed, and then formed two rotating (accretion) disks orbiting the central black hole. For the OB stars in the central arcsecond, on the other hand, a stellar merger model is the most appealing explanation. These stars may thus be "super-blue stragglers," formed and "rejuvenated" through mergers of lower mass stars in the very dense (≥108 M☉ pc-3) environment of the cusp. The "collider model" also accounts for the lack of giants within the central few arcseconds. The star closest to Sgr A* in 2002, S2, exhibits a 3.8 μm excess. We propose that the mid-IR emission comes either from the accretion flow around the black hole itself or from dust in the accretion flow that is heated by the ultraviolet emission of S2.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/0dcfe8cd82160684de18d290e732f47dc691a398

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. T. Alexander
4. Luis C. Ho
5. R. Genzel
6. M. Cappellari
7. Volker Springel
8. D. Merritt

In Atomic and Molecular Physics, and Optics

1. T. Alexander
2. R. Genzel
3. T. Ott
4. A. Eckart
5. O. Gerhard
6. S. Gillessen
7. F. Eisenhauer
8. F. Antonini

In Mechanical Engineering

1. W. N. Brandt

Citations in the corpus

• The Hubble Space TelescopeUV Legacy Survey of Galactic Globular Clusters – V. Constraints on formation scenarios (2015, background): “…of the Galactic center, where stellar densities may be even higher, and where massive stars appear to have formed, either by coalescence of less massive ones or in counter-rotating disks (Genzel et al. 2003), though conditions in the Galactic center may not be representative of those in proto-GCs.”
• Polarimetry of near-infrared flares from Sagittarius A* (2006, background): “The time difference between the observed bright polarized sub-flares is about 20 min – similar to the quasi-periodicity oscillations (QPO) reported previously (Genzel et al. 2003a).”
• The Effect of Mass Segregation on Gravitational Wave Sources near Massive Black Holes (2006, unknown): “We also adopt for our model the Galactic center valuesσ⋆ = 75 kms−1 (rh = 2pc) and n⋆ = 4 × 104 pc−3 (Genzel et al. 2003)3.”
• Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits (2008, methodology): “…of the dynamical center from S0-2’s orbit is statistically consistent with Sgr A Yradio/ IR, which is the emissive source associated with the central black hole (e.g., Melia & Falcke 2001; Genzel et al. 2003a; Ghez et al. 2004; 2005b; Hornstein et al. 2007), the solution from S0-16 is not (see Fig.”
• The Low End of the Supermassive Black Hole Mass Function: Constraining the Mass of a Nuclear Black Hole in NGC 205 via Stellar Kinematics (2005, result): “We begin by contrasting the structure of NGC 205 with that of the other wellresolved Local Group spheroids in M31, M32, M33, and the Milky Way (Lauer et al. 1992, 1998; Genzel et al. 2003).”
• An Extended Star Formation History for the Galactic Center from Hubble Space Telescope NICMOS Observations (2003, methodology): “Genzel et al. (2003) published a K-band luminosity function for stars in the central parsec, obtained with VLT/AO.”
• Composition of the galactic center star cluster - Population analysis from adaptive optics narrow band spectral energy distributions (2009, background): “The steep decline of the projected early type density towards the outer parts of the cluster (e.g. Genzel et al. 2003; Paumard et al. 2006) could be confirmed here as well (for both see Fig.1).”
• Stellar Remnants in Galactic Nuclei: Mass Segregation (2006, methodology): “This model has a central density cusp with ¼ 1:5, a value consistent with the stellar counts at the Galactic center (Alexander 1999; Genzel et al. 2003).”
• IMPROVING GALACTIC CENTER ASTROMETRY BY REDUCING THE EFFECTS OF GEOMETRIC DISTORTION (2010, background): “…hole (Eckart & Genzel 1997; Ghez et al. 1998), a disk of young stars surrounding the central supermassive black hole (Levin & Beloborodov 2003; Genzel et al. 2003; Paumard et al. 2006; Lu et al. 2009), and allowed for measurements of the orbit about the GC of the Arches, a massive young star…”
• Stellar Orbits around the Galactic Center Black Hole (2003, background): “The Sgr A* cluster stars, however, are much more concentrated toward the center where the stellar density is maximized (Genzel et al. 2003b) and the collision time is correspondingly shorter, so in this respect, merger events may be relatively favored there.”
• Stellar Dynamics in the Central Arcsecond of Our Galaxy (2003, methodology): “NoDetection of an NIR Counterpart of Sgr A* We measured a conservative limit of 5 mJy on the dereddened emission of Sgr A* at 2.2 lm, in agreement with similar measurements (Hornstein et al. 2002; Genzel et al. 2003).”
• EVIDENCE FOR LOW BLACK HOLE SPIN AND PHYSICALLY MOTIVATED ACCRETION MODELS FROM MILLIMETER-VLBI OBSERVATIONS OF SAGITTARIUS A* (2010, background): “Unlike the estimates in Broderick et al. (2009), there is no longer any allowed solution for the spin vector that aligns with either of the reported stellar disks in the inner 0.2pc of the Galactic center (Genzel et al. 2003).”
• New Physical Insights about Tidal Disruption Events from a Comprehensive Observational Inventory at X-Ray Wavelengths (2016, unknown): “Evidence for the presence of these dormant BHs in non-active Galaxies such as the one found in our Milky Way arises from mostly indirect methods (e.g., Genzel et al. 2003; Ghez et al. 2003), making it difficult to probe the properties of these interesting objects.”
• A New Distortion Solution for NIRC2 on the Keck II Telescope (2016, background): “…the discovery of the supermassive black hole and studies of its surrounding stellar population (e.g., Eckart & Genzel 1997; Ghez et al. 1998, 2005; Genzel et al. 2003; Paumard et al. 2006; Stolte et al. 2008; Bartko et al. 2009; Lu et al. 2009; Clarkson et al. 2012; Meyer et al. 2012; Yelda et…”
• An Overabundance of Transient X-Ray Binaries within 1 Parsec of the Galactic Center (2004, background): “…in the central parsec were formed either in situ either after the collision of dense molecular clouds or in a massive disk around Sgr A∗ (see, e.g., Genzel et al. 2003; Levin & Beloborodov 2003; Milosavljević & Loeb 2004), or as a cluster at larger radii that settled dynamically into the central…”
• The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics Observations (2007, background): “For example the stellar density in the central arcsecond of the GC is estimated to be > 3× 107 M⊙ pc−3 (Genzel et al. 2003).”
• Ejection of Hypervelocity Stars by the (Binary) Black Hole in the Galactic Center (2003, background): “The Milky Way, as well as most nearby elliptical galaxies and disk galaxies with spheroids, is believed to house a massive black hole (BH) at its center (e.g. Schödel et al. 2002; Genzel et al. 2003; Schödel et al. 2003; Eisenhauer et al. 2003; Ghez et al. 2003a,b,c; Gebhardt et al. 2003).”