scholarly journals The Central Dark Mass of the Milky Way

2001 ◽  
Vol 205 ◽  
pp. 20-27
Author(s):  
A. Eckart ◽  
R. Genzel ◽  
T. Ott
Keyword(s):  
Milky Way ◽  
Compact Object ◽  
Early Type ◽  
Proper Motions ◽  
Solar Mass ◽  
Stellar Orbits ◽  
Stellar Cluster ◽  
Sagittarius A ◽  
Compact Radio Source ◽  
Early Type Stars

Measurements of the proper motions and radial velocities of stars in the central cluster of the Milky Way have revealed the presence of a 2-3 million solar mass black hole at the position of the compact radio source Sagittarius A* (SgrA*). The overall stellar motions do not deviate strongly from isotropy and are consistent with a spherical isothermal stellar cluster. Speckle spectroscopy with SHARP at the NTT and slit spectroscopy with ISAAC at the VLT suggests that several of them are early type stars. This is consistent with the idea that these stars are members of an early type cluster with small angular momentum and therefore are now in the immediate vicinity of SgrA*. Most recent data now allows to measure the curvatures of the stellar orbits for a few of the stars that are closest to the center and have the largest proper motions of up to 1400 km/s. The curvatures indicate that the stars indeed orbit the central compact object and will allow to further determine its mass and compactness.

scholarly journals Blue extreme disk-runaway stars with Gaia EDR3

2021 ◽  
Vol 646 ◽  
pp. L4
Author(s):  
Andreas Irrgang ◽  
Markus Dimpel ◽  
Ulrich Heber ◽  
Roberto Raddi
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Galactic Disk ◽  
Space Mission ◽  
Early Type ◽  
Proper Motions ◽  
Supermassive Black Hole ◽  
Early Type Stars ◽  
Runaway Stars ◽  
Potential Origin

Since the discovery of hypervelocity stars in 2005, it has been widely believed that only the disruption of a binary system by a supermassive black hole at the Galactic center (GC), that is, the so-called Hills mechanism, is capable of accelerating stars to beyond the Galactic escape velocity. In the meantime, however, driven by the Gaia space mission, there is mounting evidence that many of the most extreme high-velocity early-type stars at high Galactic latitudes do originate in the Galactic disk and not in the GC. Moreover, the ejection velocities of these extreme disk-runaway stars exceed the predicted limits of the classical scenarios for the production of runaway stars. Based on proper motions from the Gaia early data release 3 and on recent and new spectrophotometric distances, we studied the kinematics of 30 such extreme disk-runaway stars, allowing us to deduce their spatial origins in and their ejection velocities from the Galactic disk with unprecedented precision. Only three stars in the sample have past trajectories that are consistent with an origin in the GC, most notably S5-HVS 1, which is the most extreme object in the sample by far. All other program stars are shown to be disk runaways with ejection velocities that sharply contrast at least with classical ejection scenarios. They include HVS 5 and HVS 6, which are both gravitationally unbound to the Milky Way. While most stars originate from within a galactocentric radius of 15 kpc, which corresponds to the observed extent of the spiral arms, a group of five stars stems from radii of about 21−29 kpc. This indicates a possible link to outer Galactic rings and a potential origin from infalling satellite galaxies.

Some Peculiar Early-Type Stars in the Southern Milky Way (1 = 237° - 332°)

1976 ◽  
Vol 32 ◽  
pp. 329-341
Author(s):  
Hans Rickman
Keyword(s):  
Milky Way ◽  
Early Type ◽  
European Southern Observatory ◽  
Early Type Stars ◽  
Spectral Survey

SummaryIn the course of the Stockholm Observatory Spectral Survey of the Southern Milky Way apparent peculiarities have been found in a number of stars of early spectral types. Some of these stars have been subject to further observations at the European Southern Observatory in Chile. A list of the stars at present considered as peculiar is presented together with finding charts in view of forthcoming observations. The list contains all pieces of information collected up to the present time for each one of the stars.

scholarly journals Kozai resonance model for Sagittarius A* stellar orbits

2006 ◽  
Vol 2 (S238) ◽  
pp. 201-206 ◽  
Author(s):  
Ladislav Šubr ◽  
Vladimír Karas ◽  
Jaroslav Haas
Keyword(s):  
Galactic Centre ◽  
Tidal Disruption ◽  
Resonance Mechanism ◽  
Resonance Model ◽  
Stellar Orbits ◽  
Stellar Cluster ◽  
Sagittarius A ◽  
Sgr A ◽  
Different Sources ◽  
Kozai Resonance

AbstractWe study a possibility of tidal disruptions of stars orbiting a supermassive black hole due to eccentricity oscillations driven by Kozai's mechanism. We apply the model to conditions relevant for the Galactic Centre where we consider two different sources of the perturbation to the central potential, which trigger the resonance mechanism. Firstly, it is a disc of young massive stars orbiting Sgr A* atr≳ 0.08 pc, and, secondly, a molecular circumnuclear disc. Each of the two possibilities appears to be capable of exciting eccentricities to values sufficient for the tidal disruption of ∼100 stars from the nuclear stellar cluster on a time-scale of 0.1–10 Myrs. Tidally disrupted stars may cause periods of increased accretion activity of Sgr A*.

scholarly journals Radial velocities of early-type stars

1970 ◽  
Vol 38 ◽  
pp. 290-290
Author(s):  
J. P. Kaufmann
Keyword(s):  
Velocity Gradient ◽  
Milky Way ◽  
Radial Velocities ◽  
Circular Motion ◽  
The Sun ◽  
Spectral Classification ◽  
Early Type ◽  
Objective Prism ◽  
Minimum Distances ◽  
Early Type Stars

With the Fehrenbach objective prism radial velocities of about 700 stars of type B0 to A0 were determined in two fields of the Southern Milky Way (lII = 295° bII = −0.6°; lII = 320° bII = −2.5°), with a mean error of ±20 km s−1. An additional photographic UBV-photometry with plates of the ADH-telescope at Boyden Observatory was accomplished. Minimum distances for the stars resulted from absorption-corrected magnitudes and a MK-spectral classification. About 200 stars lay at distances greater than 1.5 kpc from the sun. The largest distances determined were 5 kpc. From the radial velocities and distances circular velocities were derived and plotted against galactocentric distances R. Even within the possible error limits a positive velocity gradient showed up in the range 8 kpc < R < 9.5 kpc, which French authors had already found for the region 10.5 kpc < R < 12.5 kpc. If there do not exist significant deviations from circular motion for these stars, a conformity with Schmidt's 1965 model cannot be obtained.

scholarly journals Constraining the Variability and Binary Fraction of Galactic Center Young Stars

2016 ◽  
Vol 11 (S322) ◽  
pp. 237-238
Author(s):  
Abhimat K. Gautam ◽  
Tuan Do ◽  
Andrea M. Ghez ◽  
Jessica R. Lu ◽  
Mark R. Morris ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Adaptive Optics ◽  
Binary Systems ◽  
Main Sequence ◽  
Milky Way ◽  
Galactic Center ◽  
Young Stars ◽  
Early Type ◽  
Eclipsing Binary ◽  
Early Type Stars

AbstractWe present constraints on the variability and binarity of young stars in the central 10 arcseconds (~ 0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment’s photometric uncertainties, at least 36% of our sample’s known early-type stars are variable. We identified eclipsing binary systems by searching for periodic variability. In our sample of spectroscopically confirmed and likely early-type stars, we detected the two previously discovered GC eclipsing binary systems. We derived the likely binary fraction of main sequence, early-type stars at the GC via Monte Carlo simulations of eclipsing binary systems, and find that it is at least 32% with 90% confidence.

scholarly journals The Assembly History of the Milky Way Nuclear Star Cluster

2015 ◽  
Vol 12 (S316) ◽  
pp. 50-54
Author(s):  
A. Feldmeier-Krause ◽  
N. Neumayer ◽  
R. Schödel ◽  
A. Seth ◽  
P. T. de Zeeuw ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Star Clusters ◽  
Star Cluster ◽  
Reference Object ◽  
Early Type ◽  
Distinct Component ◽  
History Of ◽  
Early Type Stars ◽  
Integral Field Spectrograph

AbstractWithin the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.

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