scholarly journals Sgr A* envelope explosion and the young stars in the centre of the Milky Way

2018 ◽  
Vol 478 (1) ◽  
pp. L127-L131 ◽  
Author(s):  
Sergei Nayakshin ◽  
Kastytis Zubovas
Keyword(s):  
Milky Way ◽  
Young Stars ◽  
Sgr A

scholarly journals Central Molecular Zone of the Milky Way: Star Formation in an extreme Environment

2015 ◽  
Vol 11 (S315) ◽  
pp. 163-166
Author(s):  
Jens Kauffmann
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Spatial Scales ◽  
Extreme Environment ◽  
Average Density ◽  
High Mass ◽  
Density Structure ◽  
Star Formation Activity ◽  
Order Of Magnitude ◽  
Sgr A

AbstractThe Central Molecular Zone (CMZ; inner ~100 pc) hosts some of the most dense and massive molecular clouds of the Milky Way. These clouds might serve as local templates for dense clouds seen in nearby starburst galaxies or in the early universe. The clouds have a striking feature: they form stars at a very slow pace, considering their mass and high average density. Here we use interferometer data from ALMA and the SMA to show that this slow star formation is a consequence of the cloud density structure: CMZ clouds have a very flat density structure. They might, for example, exceed the average density of the Orion A molecular cloud by an order of magnitude on spatial scales ~5 pc, but CMZ “cores” of ~0.1 pc radius have masses and densities lower than what is found in the Orion KL region. This absence of highest–density gas probably explains the suppression of star formation. The clouds are relatively turbulent, and ALMA observations of H2CO and SiO indicate that the turbulence is induced by high–velocity shocks. We speculate that these shocks might prevent the formation of high–mass cores. It has been argued that the state of CMZ clouds depends on their position along the orbit around Sgr A*. Our incomplete data indicate no evolution in the density structure, and only a modest evolution in star formation activity per unit mass.

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.

scholarly journals The Impact of Stellar Rotation on the Nitrogen Abundance Gradient from OB Stars in the Galactic Disk

2004 ◽  
Vol 215 ◽  
pp. 226-227
Author(s):  
Simone Daflon ◽  
Katia Cunha
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Young Stars ◽  
Evolutionary Models ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Ob Stars ◽  
Nitrogen Abundance ◽  
N Enrichment ◽  
The Impact

Massive young stars can be used to trace the current chemical composition of the Galactic disk and to define its metallicity gradient. However, evolutionary models of massive rotating stars predict changes of the surface abundances due to rotationally induced mixing. The abundance analysis of elements sensitive to mixing, such as CNO, can be used to test these rotating stellar models. In this study we identify those stars that show one particular signature of mixing, N-enrichment, in our sample of 70 OB stars for which we have conducted an abundance analysis. This sample is used to define radial metallicity gradients in the Milky Way and we investigate the variation of the calculated nitrogen gradient after the exclusion of these, probably mixing-induced, N-rich stars.

scholarly journals Testing the No-Hair Theorem with Sgr A*

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Tim Johannsen
Keyword(s):  
Black Hole ◽  
Free Parameter ◽  
Milky Way ◽  
Very Long Baseline Interferometry ◽  
Angular Size ◽  
High Brightness ◽  
Supermassive Black Hole ◽  
Long Baseline ◽  
Nearby Stars ◽  
Sgr A

The no-hair theorem characterizes the fundamental nature of black holes in general relativity. This theorem can be tested observationally by measuring the mass and spin of a black hole as well as its quadrupole moment, which may deviate from the expected Kerr value. Sgr A*, the supermassive black hole at the center of the Milky Way, is a prime candidate for such tests thanks to its large angular size, high brightness, and rich population of nearby stars. In this paper, I discuss a new theoretical framework for a test of the no-hair theorem that is ideal for imaging observations of Sgr A* with very long baseline interferometry (VLBI). The approach is formulated in terms of a Kerr-like spacetime that depends on a free parameter and is regular everywhere outside of the event horizon. Together with the results from astrometric and timing observations, VLBI imaging of Sgr A* may lead to a secure test of the no-hair theorem.

scholarly journals Interarm islands in the Milky Way – the one near the Cygnus spiral arm

2020 ◽  
Vol 494 (1) ◽  
pp. 1134-1142
Author(s):  
Jacques P Vallée
Keyword(s):  
Observational Data ◽  
Milky Way ◽  
Young Stars ◽  
H Ii Regions ◽  
Spiral Arms ◽  
The Galaxy ◽  
The One ◽  
Loop 2 ◽  
Perseus Arm ◽  
Spiral Arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

scholarly journals Young Stars at the Center of the Milky Way?

2004 ◽  
Vol 602 (2) ◽  
pp. 760-769 ◽  
Author(s):  
A. Eckart ◽  
J. Moultaka ◽  
T. Viehmann ◽  
C. Straubmeier ◽  
N. Mouawad
Keyword(s):  
Milky Way ◽  
Young Stars

10.3. Progress toward a trigonometric parallax of Sgr A∗

1998 ◽  
Vol 184 ◽  
pp. 435-436
Author(s):  
M. J. Reid ◽  
A. C. S. Readhead ◽  
R. Vermeulen ◽  
R. Treuhaft
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
The Sun ◽  
Secular Motion ◽  
Extragalactic Source ◽  
Trigonometric Parallax ◽  
Sgr A ◽  
Harlow Shapley ◽  
Astronomy And Astrophysics

In 1918, Harlow Shapley first noted that globular clusters were concentrated toward the constellation of Sagittarius, and hence the Sun was not near the center of the Milky Way. Since that time astronomers have expended considerable effort to determine the distance to the center of the Milky Way, because any change in the value of this distance, R0, has a widespread impact on astronomy and astrophysics. Beginning in 1991, we have conducted observations with the VLBA designed to make possible a program to measure the distance to the Galactic Center via a trigonometric parallax. This could be accomplished with the VLBA using Sgr A∗ as a phase reference for one or more (weaker) compact extragalactic sources. A time series of measurements of the position of Sgr A∗ relative to an extragalactic source should show the effects of the annual ≈ ±0.12 mas signature of the Earth's orbit around the Sun (trigonometric parallax), as well as the ≈ 6 mas yr−1 secular motion caused by the Sun's orbit around the Galactic Center.

Stellar Populations in the Galactic Bulge

1996 ◽  
Vol 169 ◽  
pp. 317-327
Author(s):  
H.J. Habing
Keyword(s):  
Milky Way ◽  
Stellar Populations ◽  
Galactic Bulge ◽  
Central Cluster ◽  
Intimate Connection ◽  
The Subject ◽  
Sgr A

In this review I discuss stars in the bulge of our Milky Way, but I exclude stars within a few parsec from Sgr A West; they are the subject of other reviews at this Symposium. We should, however, not forget that there may be an intimate connection between the central cluster and the bulge: bulge stars may eject matter that feeds the monster at the center and eruptions by this monster may have an important effect on the bulge.

scholarly journals Understanding our Galaxy: from the center to outskirts

2007 ◽  
Vol 3 (S248) ◽  
pp. 470-473
Author(s):  
Z. Q. Shen ◽  
Y. Xu ◽  
J. L. Han ◽  
X. W. Zheng
Keyword(s):  
Magnetic Fields ◽  
Radio Source ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Disk ◽  
Spiral Arms ◽  
Compact Radio Source ◽  
Sgr A ◽  
Spiral Arm

AbstractWe describe the efforts to understand our Milky Way Galaxy, from its center to outskirts, including (1) the measurements of the intrinsic size of the galactic center compact radio source Sgr A*; (2) the determination of the distance from the Sun to the Perseus spiral arm; and (3) the revealing of large scale global magnetic fields of the Galaxy.With high-resolution millimeter-VLBI observations, Shen et al. (2005) have measured the intrinsic size of the radio-emitting region of the galactic center compact radio source Sgr A* to be only 1 AU in diameter at 3.5 mm. When combined with the lower limit on the mass of Sgr A*, this provides strong evidence for Sgr A* being a super-massive black hole. Comparison with the intrinsic size detection at 7 mm indicates a frequency-dependent source size, posing a tight constraint on various theoretical models.With VLBI phase referencing observations, Xu et al. (2006) have measured the trigonometric parallax of W3OH in the Perseus spiral arm with an accuracy of 10 μas and also its absolute velocity with an accuracy of 1 km s−1. This demonstrates the capability of probing the structure and kinematics of the Milky Way by determining distances to 12 GHz methanol (CH3OH) masers in star forming regions of distant spiral arms and Milky Way's outskirts.With pulsar dispersion measures and rotation measures, Han et al. (2006) can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the most inner Norma arm to the outer Perseus arm.

scholarly journals IS THERE A SUPERMASSIVE BLACK HOLE AT THE CENTER OF THE MILKY WAY?

2009 ◽  
Vol 18 (06) ◽  
pp. 889-910 ◽  
Author(s):  
MARK J. REID
Keyword(s):  
Black Hole ◽  
Radio Source ◽  
Milky Way ◽  
Mass Density ◽  
Apparent Size ◽  
Central Mass ◽  
Infrared Wavelength ◽  
Supermassive Black Hole ◽  
Focal Position ◽  
Sgr A

This review outlines the observations that now provide an overwhelming scientific case that the center of the Milky Way harbors a supermassive black hole. Observations at infrared wavelength trace stars that orbit about a common focal position and require a central mass (M) of 4 × 106 M⊙ within a radius of 100 AU. Orbital speeds have been observed to exceed 5,000 km s-1. At the focal position there is an extremely compact radio source (Sgr A*), whose apparent size is near the Schwarzschild radius (2GM/c2). This radio source is motionless at the ~ 1 km s-1 level at the dynamical center of the Galaxy. The mass density required by these observations is now approaching the ultimate limit of a supermassive black hole within the last stable orbit for matter near the event horizon.

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