Probing the properties of the Milky Way's central supermassive black hole with stellar orbits

Abstract

We report new precision measurements of the properties of our Galaxy's supermassive black hole. Based on astrometric (1995Y2007) and radial velocity (RV; 2000Y2007) 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 (R 0) of 8:0 AE 0:6 kpc, the enclosed mass (M bh) of 4:1 AE 0:6 ; 10 6 M , and the black hole's RV, which is consistent with zero with 30 km s À1 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 R 0 ¼ 8:4 AE 0:4 kpc and M bh ¼ 4:5 AE 0:4 ; 10 6 M. More complex models constrain the extended dark mass distribution to be less than 3Y4 ; 10 5 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 R 0 and the Galaxy's local rotation speed, which it is derived from combining R 0 with the apparent proper motion of Sgr A Ã , (0 ¼ 229 AE 18 km s À1), 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 M bh-relation.

Gravitational redshift/blueshift of light emitted by geodesic test particles, frame-dragging and pericentre-shift effects, in the Kerr–Newman–de Sitter and Kerr–Newman black hole geometries

“…The physical relevance of the graphs in Figs. 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19, 20 and 21 lies in the following fact: the local extrema of the radial profiles of the specific energy and specific angular momentum of particles on equatorial circular orbits given by the relations (26) and (27) correspond to the marginally stable orbits that we shall discuss later. The apparent singularity that appears in some graphs for negative cosmological constant e.g.…”

“…The orbits of short period stars in the central arcsecond (S-stars) of the Milky Way Galaxy provide the best current evidence for the existence of supermassive black holes, in particular for the galactic centre SgrA* supermassive black hole [13][14][15][16][17].…”

“…Moreover, we derive novel exact expressions for the frame dragging effect for particles in spherical, non-equatorial orbits in KNdS and KN black hole geometries. These results could be of interest to the observational astronomers of the Galactic centre [13,14,16,17] whose aim is to measure experimentally, the relativistic effects predicted by the theory of General Relativity [28,[56][57][58][59][60][61][62][63][64][65][66][67][68] for the observed orbits of short-period stars-the so called S-stars in our Galactic centre. During 2018, the close proximity of the star S2 (S02) to the supermassive Galactic centre black hole allowed the first measurements of the relativistic redshift observable by the GRAVITY collaboration [69] and the UCLA Galactic centre group whose astrometric measurements were obtained at the W.M.…”

“…Typical behaviour of these functions is displayed in Figs. 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19, 20 and 21. Furthermore, we investigate the stability of such timelike circular equatorial geodesics in Kerr-Newman-de Sitter spacetime and derive a new condition that restricts their radii, namely the inequality (34).…”

γ-radiation from the Galactic Center: dark matter annihilation or more conservative astrophysical models?

“…Recently it was shown [30,31] that it is possible to constrain the parameters of the DM distribution possible present around the Galactic Center by considering the induced apoastron shift due to the presence of this DM sphere and either available data obtained with the present generation of telescopes (the so called conservative limit) and also expectations from future NGLT observations or with other advanced observational facilities.…”