Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits

By A. Ghez, S. Salim, N. Weinberg, Jessica R. Lu, T. Do, J. Dunn, K. Matthews, Mark R. Morris, S. Yelda, E. Becklin and 3 more. 2008

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We report new precision measurements of the properties of our Galaxy’s supermassive black hole. Based on astrometric (1995-2007) and radial velocity (RV; 2000-2007) measurements from the W. M. Keck 10 m telescopes, a fully unconstrained Keplerian orbit for the short-period star S0-2 provides values for the distance (R0) of 8.0 ± 0.6 kpc, the enclosed mass (Mbh) of 4.1 ± 0.6 × 106 M☉, and the black hole’s RV, which is consistent with zero with 30 km s−1 uncertainty. If the black hole is assumed to be at rest with respect to the Galaxy (e.g., has no massive companion to induce motion), we can further constrain the fit, obtaining R0 = 8.4 ± 0.4 kpc and Mbh = 4.5 ± 0.4 × 106 M☉. More complex models constrain the extended dark mass distribution to be less than 3-4 × 105 M☉ within 0.01 pc, ~100 times higher than predictions from stellar and stellar remnant models. For all models, we identify transient astrometric shifts from source confusion (up to 5 times the astrometric error) and the assumptions regarding the black hole’s radial motion as previously unrecognized limitations on orbital accuracy and the usefulness of fainter stars. Future astrometric and RV observations will remedy these effects. Our estimates of R0 and the Galaxy’s local rotation speed, which it is derived from combining R0 with the apparent proper motion of Sgr A*, (θ0 = 229 ± 18 km s−1), are compatible with measurements made using other methods. The increased black hole mass found in this study, compared to that determined using projected mass estimators, implies a longer period for the innermost stable orbit, longer resonant relaxation timescales for stars in the vicinity of the black hole and a better agreement with the Mbh-σ relation.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

An Update on Monitoring Stellar Orbits in the Galactic Center (2016, methodology): “For orbits fits using a combined data set of both VLTand Keck-based observations, we replace the data points of Ghez et al. (2008) by the newer publication of the same team from Boehle et al. (2016).”
Rotation Curve and Mass Distribution in the Galactic Center - From Black Hole to Entire Galaxy (2013, background): “The innermost mass structure within a few pc around the central black hole has been extensively studied by analyzing stellar kinematics (Crawford et al. 1985; Genzel and Townes 1987; Rieke and Rieke 1988; Lindqvist et al. 1992; Genzel et al. 1994, 2010; Ghez et al. 2005, 2008; Gillessen et al. 200).”
THE M31 VELOCITY VECTOR. II. RADIAL ORBIT TOWARD THE MILKY WAY AND IMPLIED LOCAL GROUP MASS (2012, neutral): “Gillessen et al. (2009) obtained R0 = 8.33 ± 0.35 kpc (consistent also with Ghez et al. 2008).”
PLANET HUNTERS: A TRANSITING CIRCUMBINARY PLANET IN A QUADRUPLE STAR SYSTEM (2012, methodology): “To better constrain the presence of additional stars not listed in the KIC that may be contaminating the Kepler aperture, we obtained near-infrared adaptive optics (AO) observations using the NIRC2 imager behind the natural guide-star (NGS) AO system on the Keck II telescope (Ghez et al. 2008).”
GALACTIC MASERS AND THE MILKY WAY CIRCULAR VELOCITY (2009, methodology): “The method described and used in this paper is flexible enough to handle these more general distribution functions and more general models for the potential of the Galaxy.”
LINE DERIVED INFRARED EXTINCTION TOWARD THE GALACTIC CENTER (2011, methodology): “…other hand, stars directly in the GC have been used to derive R0 from the dynamics of their stellar orbits around the SMBH (Eisenhauer et al. 2003b; Ghez et al. 2008; Gillessen et al. 2009), and by using the statistical parallax of the population of late-type stars in the GC (Genzel et al. 2000;…”
First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer (2017, background): “It orbits Sgr A* with a period of 16 years (Schödel et al. 2002; Ghez et al. 2008; Gillessen et al. 2017) and reaches a velocity of up to 7600 km s − 1 , that is, 2.5% the speed of light, which makes it a prime candidate to study general relativistic orbit e ﬀ ects close to a supermassive black…”
Mass models of the Milky Way (2011, methodology): “In this work we take R0 from the study of stellar orbits around the supermassive black hole at the Galactic Centre, Sgr A*, by Gillessen et al. (2009) R0 = 8.33 ± 0.35 kpc, (7) though we could equally have taken the value 8.4 ± 0.4 kpc from Ghez et al. (2008), found from similar data.”
PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES (2013, methodology): “Using the measurements of the mass and distance of Sgr A* from the monitoring of close stellar orbits (Ghez et al. 2008; Gillessen et al. 2009), Broderick et al. (2009a, 2011a) combined the VLBI observations of Sgr A* with measurements of its spectral energy distribution (Yuan et al. 2004 and…”
Adaptive Optics for Astronomy (2012, background): “This has a major impact on how well one can perform wavefront reconstruction, remove non-common 40 Davies & Kasper path errors, and compensate optical distortions.”
Galactic Searches for Dark Matter (2012, methodology): “From the astrometric and kinematic measurements of short period stars in the Galactic center, there is now conclusive evidence for a ∼ 4 × 106 M supermassive black hole in the center of the Galaxy (Ghez et al., 2008; Gillessen et al., 2009).”
A TRIGONOMETRIC PARALLAX OF Sgr B2 (2009, background): “For example, the estimate of the mass of the super-massive black hole at the Galactic Center (Sgr A*) obtained from stellar orbits is dominated by uncertainty in R0 (Ghez et al. 2008; Gillessen et al. 2009).”
IMPROVING GALACTIC CENTER ASTROMETRY BY REDUCING THE EFFECTS OF GEOMETRIC DISTORTION (2010, methodology): “Astrometry was extracted using StarFinder (Diolaiti et al. 2000) in a similar manner as in Ghez et al. (2008), with a few minor modifications.”
The Bar and Spiral Structure Legacy (BeSSeL) Survey: Mapping the Milky Way with VLBI Astrometry† (2011, methodology): “The accurate determination of stellar orbits in the Galactic center yields now consistent values from two groups of 8.4 ± 0.4 kpc (Ghez et al. 2008) and 8.33 ± 0.35 kpc (Gillessen et al. 2009).”
Masses and scaling relations for nuclear star clusters, and their co-existence with central black holes (2016, neutral): “…' 1010M (Filippenko & Ho 2003; Seth et al. 2008a, 2010; Graham & Spitler 2009; Neumayer & Walcher 2012), with the best-studied example being the center of the Milky Way (Schödel et al. 2007; Ghez et al. 2008; Gillessen et al. 2009; Genzel et al. 2010; Feldmeier et al. 2014; Schödel et al. 2014).”
THE NGC 404 NUCLEUS: STAR CLUSTER AND POSSIBLE INTERMEDIATE-MASS BLACK HOLE (2010, background): “It is an incredibly complicated environment with a black hole (MBH = 4 × 106 M⊙; Ghez et al. 2008) and a nuclear star cluster (MNSC ∼ 3 × 107 M⊙ Genzel et al. 1996; Schödel et al. 2007; Trippe et al. 2008) that contains stars of many ages and in different substructures including disks of young…”
THE ORBIT OF THE STAR S2 AROUND SGR A* FROM VERY LARGE TELESCOPE AND KECK DATA (2009, methodology): “The number of orbits has increased to more than 20 since then (Ghez et al. 2005; Eisenhauer et al. 2005; Gillessen et al. 2009) and in particular the full S2 orbit has recently been used for improved determinations of the mass and of R0 (Ghez et al. 2008; Gillessen et al. 2009).”