The Population I Core of the Galaxy

1994 ◽  
Vol 11 (2) ◽  
pp. 191-193 ◽  
Author(s):  
David Allen ◽  
Michael Burton
Keyword(s):  
Mass Loss ◽  
Radio Source ◽  
Galactic Centre ◽  
Overtone Band ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
Sgr A

Abstract We demonstrate the presence of a cluster of hot, population I stars at the very centre of the Galaxy, using the depth of the first overtone band of CO and the presence of emission in He I 2 ·058 μm and [Fell] 1·644μm to identify stars. The cluster is very compact and comprises at least several hundred stars. They lie close to the nonthermal radio source Sgr A* and dominate the luminosity and mass loss of the Galactic core. Their presence suggests that a starburst occurred at the Galactic centre.

scholarly journals The Compact Nonthermal Radio Source at the Galactic Center: an Update

1989 ◽  
Vol 136 ◽  
pp. 527-534
Author(s):  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Central Star ◽  
Radio Sources ◽  
Stellar Objects ◽  
Nonthermal Radio ◽  
Compact Radio Source ◽  
The Galaxy ◽  
Observational Status ◽  
Sgr A

We review the current observational status of Sgr A∗, the compact nonthermal radio source at the galactic center. Sgr A∗ is a unique radio source at a unique location of the Galaxy. It is unlike any compact radio source associated with known stellar objects, but it is similar to extragalactic nuclear compact radio sources. The positional offset between Sgr A∗ and IRS16 places little constraint on the nature of the underlying energy source, since IRS16 need not be the core of the central star cluster. Sgr A∗ is still the best candidate for marking the location of a massive collapsed object.

scholarly journals 10.4. Multi-wavelength VLBA mapping of Sgr A∗

1998 ◽  
Vol 184 ◽  
pp. 437-438
Author(s):  
Zhi-Qiang Shen ◽  
K. Y. Lo ◽  
Jun-Hui Zhao ◽  
Paul Ho
Keyword(s):  
Energy Source ◽  
Black Hole ◽  
Radio Source ◽  
Radio Sources ◽  
Massive Black Hole ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
Multi Wavelength ◽  
Sgr A ◽  
Source Structure

Sgr A∗, the enigmatic compact nonthermal radio source located at the center of the Galaxy for many years has been considered as the signpost of a massive black hole (Rees 1982; Lo 1986; Falcke et al. 1997). Its properties are unique in the Galaxy, but it resembles other nuclear radio sources (Lo 1993). Efforts to delineate the source structure of Sgr A∗, in order to constraint the nature of the underlying energy source, have been ongoing since 1975 (Lo et al. 1975).

The Velocities of 6cm Recombination Line Emission originating near the Galactic Nucleus

1977 ◽  
Vol 3 (2) ◽  
pp. 150-152 ◽  
Author(s):  
F. F. Gardner ◽  
J. B. Whiteoak
Keyword(s):  
Radio Source ◽  
Strong Evidence ◽  
Line Emission ◽  
Hii Regions ◽  
Galactic Centre ◽  
Recombination Line ◽  
The Galaxy ◽  
Centre Region ◽  
Sgr A

Although it is well known that HII regions are present in the innermost regions of the Galaxy their kinematics are still not fully understood. In one study Pauls et al. (1976) surveyed with a beamwidth of 3′ arc the 10 GHz recombination line emission in directions within 15′ arc of the nuclear radio source Sgr A. They found that the emission velocities varied from position to position within the range -50 to + 50 km s-1but appeared to lack any overall pattern. In contrast, we have recently observed the recombination line emission from the galactic centre region with a beamwidth of 4′.5 arc, and find strong evidence of ordered motions near the galactic nucleus.

scholarly journals An Upper Limit to the Mass Loss from the Centre of the Galaxy

1974 ◽  
Vol 64 ◽  
pp. 36-36
Author(s):  
Arcadio Poveda ◽  
Christine Allen
Keyword(s):  
Mass Loss ◽  
Gravitational Waves ◽  
Mass Distribution ◽  
Globular Clusters ◽  
Loss Rate ◽  
Galactic Centre ◽  
Isotropic Source ◽  
The Past ◽  
Upper Limit ◽  
The Galaxy

A mass loss of 200 M⊙ per year, as conservatively suggested if Weber is detecting gravitational waves from an isotropic source at the galactic centre, is shown to be incompatible with the existence of (a) globular clusters, (b) old wide binaries, if this loss rate has been constant over the past 1010 yr.From the orbit of ω Centauri in the galactic field and its observed mass distribution and tidal radius an upper limit to the mass loss from the galactic centre is found to be 1 M⊙ yr-1 over the past 1010 yr.

scholarly journals The Radio Spectrum of SGR A∗

1996 ◽  
Vol 171 ◽  
pp. 342-342 ◽  
Author(s):  
T. Beckert ◽  
W.J. Duschl ◽  
P.G. Mezger ◽  
R. Zylka
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Radio Spectrum ◽  
Frequency Range ◽  
Upper Limits ◽  
The Galaxy ◽  
Sgr A

Sgr A∗, the enigmatic radio source located at the dynamical center of the Galaxy, is firmly detected in the frequency range of ∼ 1 – few 102 GHz. For ∼ 0.5 – 1 GHz and in the MIR range only significant upper limits of the flux density are known. Between ∼ 1.5 and 600 GHz the time averaged flux density Sv is proportional to v1/3 (v: frequency). For frequencies higher than ∼ 600 GHz as well as for those lower than ∼ 1.5 GHz, Sv drops sharply.

Sagittarius A

1967 ◽  
Vol 31 ◽  
pp. 393-404 ◽  
Author(s):  
J. Lequeux
Keyword(s):  
Short Wave ◽  
Galactic Centre ◽  
High Angular Resolution ◽  
Thermal Source ◽  
Thermal Index ◽  
Sagittarius A ◽  
The Galaxy ◽  
External Galaxies ◽  
Sgr A ◽  
Thermal Sources

The available high-resolution observations of the complex of radio sources in the region of the galactic centre are reviewed and analysed. As noted by Downes and Maxwell, the spectrum of the strong central source, Sagittarius A, is markedly non-thermal (index 0·7) at high frequencies; below 3000 MHz the spectrum may be flat, but flux values obtained at high angular resolution are badly needed.Various arguments indicate that the whole source complex is located near the nucleus of the Galaxy. From the short-wave observations collected by Downes and Maxwell dimensions, densities and masses are estimated for the thermal sources. The total mass of ionized hydrogen in these sources is about 106M⊙; the mechanism of ionization is uncertain.The non-thermal source Sgr A may be similar to the optical nuclei of external galaxies. Its synchrotron emission, as well as the outward motions and tilted features observed in the 21-cm line and continuum, are signs of activity in the galactic nucleus; but the time-scales of the various phenomena appear to disagree.

scholarly journals The Galactic Center

1984 ◽  
Vol 110 ◽  
pp. 265-273
Author(s):  
K. Y. Lo
Keyword(s):  
High Resolution ◽  
Radio Source ◽  
Galactic Center ◽  
Minor Axis ◽  
Ionized Gas ◽  
Nonthermal Radio ◽  
The Galaxy ◽  
First Time ◽  
Source Structure

The center of our Galaxy contains an extremely compact nonthermal radio source. For the first time, elongation in the source structure has been detected. The long axis is nearly aligned with the minor axis of the Galaxy. Recent high resolution observations of the ionized gas within the central 3 parsecs suggest that matter may be falling in towards the center. This has interesting implications on the processes within our Galactic nucleus.

scholarly journals Discovery of a nearby 1700 km s−1 star ejected from the Milky Way by Sgr A*

2019 ◽  
Vol 491 (2) ◽  
pp. 2465-2480 ◽  
Author(s):  
Sergey E Koposov ◽  
Douglas Boubert ◽  
Ting S Li ◽  
Denis Erkal ◽  
Gary S Da Costa ◽  
...  
Keyword(s):  
Main Sequence ◽  
Orbital Plane ◽  
Galactic Centre ◽  
Ejection Velocity ◽  
Solar Motion ◽  
Current Location ◽  
Annular Disc ◽  
The Galaxy ◽  
Sgr A ◽  
Geometry And Kinematics

ABSTRACT We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a ∼2.35 M⊙ A-type star located at a distance of ∼9 kpc from the Sun and has a heliocentric radial velocity of 1017 ± 2.7 $\mathrm{\, km\, s^{-1}}$ without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 $\mathrm{\, km\, s^{-1}}$. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of ∼1800 $\mathrm{\, km\, s^{-1}}$ and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy,⊙ = 246.1 ± 5.3 $\mathrm{\, km\, s^{-1}}$ or position R0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.

scholarly journals IRTF/TEXES observations of the H ii regions H1 and H2 in the Galactic Centre

2017 ◽  
Vol 470 (1) ◽  
pp. 561-575 ◽  
Author(s):  
Hui Dong ◽  
John H. Lacy ◽  
Rainer Schödel ◽  
Francisco Nogueras-Lara ◽  
Teresa Gallego-Calvente ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Galactic Center ◽  
Galactic Centre ◽  
H Ii Regions ◽  
Stellar Cluster ◽  
The Galaxy ◽  
H Ii Region ◽  
Sgr A ◽  
Projected Distance

Abstract We present new [Ne ii] (12.8 μm) IRTF/TEXES observations of the Galactic Center H ii regions H1 and H2, which are at a projected distance of ∼11 pc from the centre of the Galaxy. The new observations allow us to map the radial velocity distributions of ionized gas. The high spectroscopic resolution (∼4 km s−1) helps us to disentangle different velocity components and enables us to resolve previous ambiguity regarding the nature of these sources. The spatial distributions of the intensity and radial velocity of the [Ne ii] line are mapped. In H1, the intensity distributions of the Paschen-α (1.87 μm) and [Ne ii] lines are significantly different, which suggests a strong variation of extinction across the H ii region of AK ∼ 0.56. The radial velocity distributions across these H ii regions are consistent with the predictions of a bow-shock model for H1 and the pressure-driven model for H2. Furthermore, we find a concentration of bright stars in H2. These stars have similar H − Ks colours and can be explained as part of a 2-Myr-old stellar cluster. H2 also falls on the orbit of the molecular clouds, suggested to be around Sgr A*. Our new results confirm what we had previously suggested: The O supergiant P114 in H1 is a runaway star, moving towards us through the −30 to 0 km s−1 molecular cloud, whereas the O If star P35 in H2 formed in situ, and may mark the position of a so-far unknown small star cluster formed within the central 30 pc of the Galaxy.

High-resolution VLBA imaging of the radio source Sgr A* at the Galactic Centre

Nature ◽  
1993 ◽  
Vol 362 (6415) ◽  
pp. 38-40 ◽  
Author(s):  
K. Y. Lo ◽  
D. C. Backer ◽  
K. I. Kellermann ◽  
M. Reid ◽  
J. H. Zhao ◽  
...  
Keyword(s):  
High Resolution ◽  
Radio Source ◽  
Galactic Centre ◽  
Sgr A
Sign in / Sign up

Export Citation Format

Share Document