scholarly journals Hot stars in the Galactic Center

1999 ◽  
Vol 193 ◽  
pp. 449-458
Author(s):  
Andreas Eckart ◽  
Thomas Ott ◽  
Reinhard Genzel ◽  
Dieter Lutz
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Galactic Center ◽  
Hot Stars ◽  
Massive Black Hole ◽  
Central Cluster ◽  
Short Period ◽  
Sgr A

The central parsec of our Galaxy is powered by a cluster of young massive hot stars which formed a few million years ago. Within that cluster the seven most luminous (L >105.75 L⊙) and moderately hot (T < 104.5 K) blue supergiants contribute half of the ionizing luminosity of that region. These stars probably formed when a dense cloud fell into the center < 107 years ago, was highly compressed there, and became gravitationally unstable. Over six years of high spatial resolution, near-infrared imaging and spectroscopy have made it possible to carry out a detailed investigation of the stars in the central cluster and its enclosed mass. As one result of a detailed variability study of the central cluster stars we found that the bright He I star IRS 16SW is a short-period variable with a period of ∼9.72 days. It is most likely an eclipsing binary with a lower mass limit of 100 solar masses. Line of sight velocities and proper motions have been measured for these hot stars (as well as ∼200 other stars) down to separations of less than five light days from the compact radio source Sgr A* at the dynamic center of the Milky Way. These confirmed measurements imply the presence of a central dark mass of 2.6 × 106 solar masses. The dark mass at the center of the Milky Way is currently the most compelling case for a massive black hole. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants, substellar condensations or a degenerate gas of elementary particles but that at least 103 to 105 solar masses must be in the form of a massive black hole associated with Sgr A* itself.

scholarly journals 10.1. The nuclear star cluster of the Milky Way: star formation and central dark mass

1998 ◽  
Vol 184 ◽  
pp. 421-431 ◽  
Author(s):  
R. Genzel ◽  
A. Eckart
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Active Phase ◽  
Star Cluster ◽  
Structure Evolution ◽  
Massive Black Hole ◽  
Imaging And Spectroscopy ◽  
Sgr A

High spatial resolution, near-infrared imaging and spectroscopy of the nuclear star cluster obtained in the last few years have given key new insights about the structure, evolution and mass distribution in the Milky Way Center. The central parsec is powered by a cluster of hot, massive stars. Their characteristics imply that there was an active phase of star formation a few million years ago, probably triggered by the infall and collapse of a very dense gas cloud. Other such starburst episodes may have taken place between 100 and 300 million years ago. Measurements of radial and proper motions for more than 200 stars show that stellar velocities increase with a Kepler law down to a scale of a light week from the compact radio source Sgr A∗. The data make a compelling case for the presence of a compact, central dark mass of about 2.6×106 M⊙. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants or substellar condensations. Energy equipartition requires that at least five percent of the dark mass (≥105 M⊙) must be associated with Sgr A∗ itself and likely is enclosed within less than 8 light minutes. If one accepts these arguments it is hard to escape the conclusion that Sgr A∗ is indeed a massive black hole at the core of the Milky Way.

scholarly journals A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty

2019 ◽  
Vol 625 ◽  
pp. L10 ◽  
Author(s):  
◽  
R. Abuter ◽  
A. Amorim ◽  
M. Bauböck ◽  
J. P. Berger ◽  
...  
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Galactic Center ◽  
Accurate Determination ◽  
Massive Black Hole ◽  
Geometric Distance ◽  
Significance Level ◽  
Beam Combiner ◽  
Infrared Interferometry ◽  
Sgr A

We present a 0.16% precise and 0.27% accurate determination of R0, the distance to the Galactic center. Our measurement uses the star S2 on its 16-year orbit around the massive black hole Sgr A* that we followed astrometrically and spectroscopically for 27 years. Since 2017, we added near-infrared interferometry with the VLTI beam combiner GRAVITY, yielding a direct measurement of the separation vector between S2 and Sgr A* with an accuracy as good as 20 μas in the best cases. S2 passed the pericenter of its highly eccentric orbit in May 2018, and we followed the passage with dense sampling throughout the year. Together with our spectroscopy, in the best cases with an error of 7 km s−1, this yields a geometric distance estimate of R0 = 8178 ± 13stat. ± 22sys. pc. This work updates our previous publication, in which we reported the first detection of the gravitational redshift in the S2 data. The redshift term is now detected with a significance level of 20σ with fredshift = 1.04 ± 0.05.

scholarly journals The (quite dark) stellar cluster around the supermassive black hole Sagittarius A* at the center of the Milky Way

2007 ◽  
Vol 3 (S245) ◽  
pp. 207-210
Author(s):  
Rainer Schödel ◽  
A. Eckart
Keyword(s):  
Black Hole ◽  
Adaptive Optics ◽  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Current Theory ◽  
Star Cluster ◽  
Massive Black Hole ◽  
Stellar Cluster ◽  
Sagittarius A

AbstractHigh-resolution seeing limited and adaptive optics near-infrared imaging observations of the stellar cluster within about one parsec of the massive black hole Sagittarius A* allow us to obtain a detailed picture of the structure of the nuclear star cluster of the Milky Way. We find that the stellar number counts and the diffuse light of the unresolved stellar population can be described very well by a stellar density function in the form of a broken-power law. This agrees well with theoretical predictions on the structure of a dynamically relaxed star cluster around a massive black hole. However, the cusp slope is found to be too shallow, which may be related to mixing of different stellar populations and continuous star formation, phenomena that are not taken into account by current theory. Mass densities larger than 107 solar masses per pc3 are reached within 0.1 pc of the central black hole. Intriguingly, up to several tens of percent of the total cluster mass in the central parsec may be in the form of dark stellar remnants.

scholarly journals 10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

1998 ◽  
Vol 184 ◽  
pp. 433-434
Author(s):  
A. M. Ghez ◽  
B. L. Klein ◽  
C. McCabe ◽  
M. Morris ◽  
E. E. Becklin
Keyword(s):  
Black Hole ◽  
Milky Way ◽  
Galactic Center ◽  
Robust Method ◽  
Proper Motions ◽  
Central Black Hole ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

Clarification of the formation process of the super massive black hole by Infrared astrometric satellite, Small-JASMINE

2017 ◽  
Vol 12 (S330) ◽  
pp. 360-361 ◽  
Author(s):  
Taihei Yano ◽  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Phase Space ◽  
Formation Process ◽  
Near Infrared ◽  
Galactic Center ◽  
Space Distribution ◽  
Massive Black Hole ◽  
Phase Space Distribution ◽  
Merging Process

AbstractSmall-JASMINE (hearafter SJ), infrared astrometric satellite, will measure the positions and the proper motions which are located around the Galactic center, by operating at near infrared wave-lengths. SJ will clarify the formation process of the super massive black hole (hearafter SMBH) at the Galactic center. In particular, SJ will determine whether the SMBH was formed by a sequential merging of multiple black holes. The clarification of this formation process of the SMBH will contribute to a better understanding of merging process of satellite galaxies into the Galaxy, which is suggested by the standard galaxy formation scenario. A numerical simulation (Tanikawa and Umemura, 2014) suggests that if the SMBH was formed by the merging process, then the dynamical friction caused by the black holes have influenced the phase space distribution of stars. The phase space distribution measured by SJ will make it possible to determine the occurrences of the merging process.

scholarly journals The Nuclear Star Cluster of the Milky Way: Star Formation, Stellar Collisions and Central Dark Mass

1996 ◽  
Vol 174 ◽  
pp. 81-90
Author(s):  
R. Genzel
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Star Cluster ◽  
Structure Evolution ◽  
Late Type ◽  
Massive Black Hole ◽  
Imaging And Spectroscopy ◽  
Central Parsec

High resolution near-infrared imaging and spectroscopy now gives detailed information about the structure, evolution and mass distribution in the nuclear star cluster of the Milky Way. The central parsec is powered by a cluster of luminous and helium rich, blue supergiants/Wolf-Rayet stars. The most likely scenario for the formation of the massive stars is a star formation burst a few million years ago at which time a dense gas cloud may have fallen into the center. The stellar density in the ∼ 0.3 pc radius central core is high enough that collisions with main sequence stars destroy the largest late type giant stars. Radial velocity measurements for about 300 early and late type stars between 0.1 and 5pc radius from the dynamic center now strongly favor the existence of a central dark mass of 2.5 − 3.3 × 106M⊙ (density (109M⊙pc−3, M/L2μm) ∼ 100M⊙/L⊙) within 0.1pc of the dynamic center. This central dark mass cannot be a cluster of neutron stars. It is either a compact cluster of stellar black holes or, most likely, a single massive black hole.

scholarly journals Observing a black hole event horizon: (sub)millimeter VLBI of Sgr A*

2009 ◽  
Vol 5 (S261) ◽  
pp. 271-276 ◽  
Author(s):  
Vincent L. Fish ◽  
Sheperd S. Doeleman
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Evidence ◽  
Galactic Center ◽  
Strong Field ◽  
Variable Component ◽  
Massive Black Hole ◽  
Black Hole Candidate ◽  
Long Baseline ◽  
Sgr A

AbstractVery strong evidence suggests that Sagittarius A*, a compact radio source at the center of the Milky Way, marks the position of a super massive black hole. The proximity of Sgr A* in combination with its mass makes its apparent event horizon the largest of any black hole candidate in the universe and presents us with a unique opportunity to observe strong-field GR effects. Recent millimeter very long baseline interferometric observations of Sgr A* have demonstrated the existence of structures on scales comparable to the Schwarzschild radius. These observations already provide strong evidence in support of the existence of an event horizon. (Sub)Millimeter VLBI observations in the near future will combine the angular resolution necessary to identify the overall morphology of quiescent emission, such as an accretion disk or outflow, with a fine enough time resolution to detect possible periodicity in the variable component of emission. In the next few years, it may be possible to identify the spin of the black hole in Sgr A*, either by detecting the periodic signature of hot spots at the innermost stable circular orbit or parameter estimation in models of the quiescent emission. Longer term, a (sub)millimeter VLBI “Event Horizon Telescope” will be able to produce images of the Galactic center emission to the see the silhouette predicted by general relativistic lensing. These techniques are also applicable to the black hole in M87, where black hole spin may be key to understanding the jet-launching region.

scholarly journals Observations of the gas cloud G2 in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 254-263
Author(s):  
S. Gillessen ◽  
R. Genzel ◽  
T. K. Fritz ◽  
F. Eisenhauer ◽  
O. Pfuhl ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Accretion Rate ◽  
Tidal Effects ◽  
Massive Black Hole ◽  
Radial Orbit ◽  
Sgr A ◽  
The Many ◽  
Gas Cloud ◽  
Luminosity Evolution

AbstractIn 2011, we discovered a compact gas cloud (“G2”) with roughly three Earth masses that is falling on a near-radial orbit toward the massive black hole in the Galactic center. The orbit is well constrained and pericenter passage is predicted for early 2014. Our data beautifully show that G2 gets tidally sheared apart due to the massive black hole's force. During the next months, we expect that in addition to the tidal effects, hydrodynamics get important, when G2 collides with the hot ambient gas around Sgr A*. Simulations show that ultimately, the cloud's material might fall into the massive black hole. Predictions for the accretion rate and luminosity evolution, however, are very difficult due to the many unknowns. Nevertheless, this might be a unique opportunity in the next years to observe how gas feeds a massive black hole in a galactic nucleus.

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