Stellar Orbits around the Galactic Center Black Hole

By A. Ghez, S. Salim, S. Hornstein, A. Tanner, Jessica R. Lu, Mark R. Morris, E. Becklin, G. Duchêne. 2003

666 citations recorded by the source corpus.

We present new diffraction-limited images of the Galactic center, obtained with the W. M. Keck I 10 m telescope. Within 0.″4 of the Galaxy's central dark mass, 17 proper-motion stars, with K magnitudes ranging from 14.0 to 16.8, are identified, and 10 of these are new detections (six were also independently discovered by others). In this sample, three newly identified (S0-16, S0-19, and S0-20) and four previously known (S0-1, S0-2, S0-4, and S0-5) sources have measured proper motions that reveal orbital solutions. Orbits are derived simultaneously so that they jointly constrain the central dark object's properties: its mass, its position, and, for the first time using orbits, its motion on the plane of the sky. This analysis pinpoints the Galaxy's central dark mass to within 1.3 mas (10 AU) and limits its proper motion to 1.5 ± 0.5 mas yr-1 (or equivalently 60 ± 20 km s-1) with respect to the central stellar cluster. This localization of the central dark mass is consistent with our derivation of the position of the radio source Sgr A* in the infrared reference frame (±10 mas) but with an uncertainty that is a factor of 8 times smaller, which greatly facilitates searches for near-infrared counterparts to the central black hole. Consequently, one previous claim for such a counterpart can now be ascribed to a close stellar passage in 1996. Furthermore, we can place a conservative upper limit of 15.5 mag on any steady state counterpart emission. The estimated central dark mass from orbital motions is 3.7(±0.2) × 106 3 M☉; this is a more direct measure of mass than those obtained from velocity dispersion measurements, which are as much as a factor of 2 smaller. The Galactic center's distance, which adds an additional 19% uncertainty in the estimated mass, is now the limiting source of uncertainty in the absolute mass. For stars in this sample, the closest approach is achieved by S0-16, which came within a mere 45 AU (=0.0002 pc = 600Rs) at a velocity of 12,000 km s-1. This increases the inferred dark mass density by 4 orders of magnitude compared to earlier analyses based on velocity and acceleration vectors, making the Milky Way the strongest existing case for a supermassive black hole at the center of a normal-type galaxy. Well-determined orbital parameters for these seven Sgr A* cluster stars also provide new constraints on how these apparently massive, young (<10 Myr) stars formed in a region that seems to be hostile to star formation. Unlike the more distant He I emission line stars—another population of young stars in the Galactic center—that appear to have coplanar orbits, the Sgr A* cluster stars have orbital properties (eccentricities, angular momentum vectors, and apoapse directions) that are consistent with an isotropic distribution. Therefore, many of the mechanisms proposed for the formation of the He I stars, such as formation from a preexisting disk, are unlikely solutions for the Sgr A* cluster stars. Unfortunately, alternative theories for producing young stars, or old stars that look young, in close proximity to a central supermassive black hole are all also somewhat problematic. Understanding the apparent youth of stars in the Sgr A* cluster, as well as the more distant He I emission line stars, has now become one of the major outstanding issues in the study of the Galactic center.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/dd1fbec00658a0ade517943c820861a088bdbf3f

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In Astronomy and Astrophysics

1. T. Alexander
2. Luis C. Ho
3. P. Hopkins
4. L. Hernquist
5. M. Volonteri
6. F. Antonini
7. D. Merritt
8. R. Genzel

Citations in the corpus

• Merging Binaries in the Galactic Center: The eccentric Kozai-Lidov mechanism with stellar evolution (2016, background): “The mass of the MBH, mMBH, remains fixed at 4×106 M (following Ghez et al. 2005; Gillessen et al. 2009) for all systems since we are mostly interested in the results for Sagittarius A?.”
• STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE (2008, background): “…1978; Rees 1988) The renewed interest in this problem is driven by observations of stars closely orbiting the Galactic MBH (Eisenhauer et al. 2005; Ghez et al. 2005) and the accumulating data on their distribution and dynamics (Alexander 1999; Genzel et al. 2000, 2003; Schödel et al. 2003, 2007),…”
• A New Sample of Low-Mass Black Holes in Active Galaxies (2007, background): “Within the inactive sample of galaxies with dynamical BH masses, the BH in M32, MBH=(2.5+3.0−2.0) × 10 6 M⊙, has the lowest mass (Tremaine et al. 2002; excluding the Milky Way, whose modern mass is 3.5×106 M⊙; e.g., Ghez et al. 2005; Eisenhauer et al. 2005).”
• Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits (2008, methodology): “A total of 27 epochs of speckle observations are included in the analysis conducted in this paper, of which 22 have been reported in earlier papers by our group (Ghez et al. 1998, 2000, 2005a).”
• Starbursts near supermassive black holes: young stars in the Galactic Centre, and gravitational waves in LISA band (2006, background): “…period of the S-star is that of S1, ¶ We acknowledge Scott Tremaine for attracting our attention to the RR as a potentially important relaxation mechanism for the S-star relaxation, in 2004. c© 0000 RAS, MNRAS 000, 000–000 which has Porb = 94yr (Eisenhauer et al., 2005, see also Ghez et al., 2005).”
• The black hole mass–stellar velocity dispersion correlation: bulges versus pseudo-bulges (2008, neutral): “…& Malkan 2007; (3) Drory & Fisher 2007; (4) Erwin et al. 2002; (5) Gadotti 2008; (6) Garcia-Rissmann et al. 2005; (7) Gebhardt et al. 2003; (8) Ghez et al. 2005; (9) Graham & Driver 2007; (10) Greenhill et al. 2003; (11) Kondratko et al. 2008; (12) Lodato & Bertin 2003; Huré 2002; (13)…”
• Polarimetry of near-infrared flares from Sagittarius A* (2006, background): “…a (3.6 ± 0.3)× 106 M Massive Black Hole (MBH) at the center of the Milky Way at the position of the compact radio source SgrA* (Eisenhauer et al. 2005; Ghez et al. 2005; Eisenhauer et al. 2003; Schödel et al. 2003; Eckart et al. 2002; Schödel et al. 2002, for a recent review see Eckart et al.…”
• MONITORING STELLAR ORBITS AROUND THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER (2008, background): “So the basic result of this study, improving measurement uncertainties by a factor of six over Schödel et al. (2002); Ghez et al. (2005); Eisenhauer et al. (2005), is that a single point mass potential is (still) the best description of the data.”
• Rotation Curve and Mass Distribution in the Galactic Center - From Black Hole to Entire Galaxy (2013, background): “The inner straight dashed line represents the central massive black hole of mass 3.6×106M⊙ (Genzel et al. 2000; Ghez et al. 2005; Gillesen et al. 2009).”