scholarly journals Structure of the nuclear stellar cluster of the Milky Way galaxy

2013 ◽  
Vol 9 (S303) ◽  
pp. 228-229
Author(s):  
Devaky Kunneriath ◽  
Rainer Schödel ◽  
Susan Stolovy ◽  
Anja Feldmeier
Keyword(s):  
Globular Clusters ◽  
Surface Brightness ◽  
Milky Way ◽  
Galactic Center ◽  
Host Galaxies ◽  
Dynamical Mass ◽  
Milky Way Galaxy ◽  
Stellar Cluster ◽  
Nuclear Cluster ◽  
Sgr A

AbstractNuclear star clusters are unambiguously detected in about 50–70% of spiral and spheroidal galaxies. They have typical half-light radii of 2–5 pc, dynamical mass ranging from 106 – 107 M⊙, are brighter than globular clusters, and obey similar scaling relations with host galaxies as supermassive black holes. The nuclear stellar cluster (NSC) which surrounds Sgr A*, the SMBH at the center of our galaxy, is the nearest nuclear cluster to us, and can be resolved to scales of milliparsecs. The strong and highly variable extinction towards the Galactic center makes it very hard to infer the intrinsic properties of the NSC (structure and size). We attempt a new way to infer its properties by using Spitzer MIR images in a wavelength range 3–8 μm where the extinction is at a minimum, and the NSC clearly stands out as a separate structure. We present results from our analysis, including extinction-corrected images and surface brightness profiles of the central few hundred parsecs of the Milky Way.

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.

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.

scholarly journals The mass fraction of halo stars contributed by the disruption of globular clusters in the E-MOSAICS simulations

2020 ◽  
Vol 493 (3) ◽  
pp. 3422-3428 ◽  
Author(s):  
Marta Reina-Campos ◽  
Meghan E Hughes ◽  
J M Diederik Kruijssen ◽  
Joel L Pfeffer ◽  
Nate Bastian ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Light Element ◽  
Element Abundance ◽  
Host Galaxies ◽  
Stellar Cluster ◽  
Halo Stars ◽  
Stellar Halo

ABSTRACT Globular clusters (GCs) have been posited, alongside dwarf galaxies, as significant contributors to the field stellar population of the Galactic halo. In order to quantify their contribution, we examine the fraction of halo stars formed in stellar clusters in the suite of 25 present-day Milky Way-mass cosmological zoom simulations from the E-MOSAICS project. We find that a median of 2.3 and 0.3 per cent of the mass in halo field stars formed in clusters and GCs, defined as clusters more massive than 5 × 103 and 105 M⊙, respectively, with the 25–75th percentiles spanning 1.9–3.0 and 0.2–0.5 per cent being caused by differences in the assembly histories of the host galaxies. Under the extreme assumption that no stellar cluster survives to the present day, the mass fractions increase to a median of 5.9 and 1.8 per cent. These small fractions indicate that the disruption of GCs plays a subdominant role in the build-up of the stellar halo. We also determine the contributed halo mass fraction that would present signatures of light-element abundance variations considered to be unique to GCs, and find that clusters and GCs would contribute a median of 1.1 and 0.2 per cent, respectively. We estimate the contributed fraction of GC stars to the Milky Way halo, based on recent surveys, and find upper limits of 2–5 per cent (significantly lower than previous estimates), suggesting that models other than those invoking strong mass loss are required to describe the formation of chemically enriched stellar populations in GCs.

scholarly journals The structure of the nuclear stellar cluster of the Milky Way

2006 ◽  
Vol 2 (S238) ◽  
pp. 187-190
Author(s):  
Rainer Schödel ◽  
Andreas Eckart
Keyword(s):  
Adaptive Optics ◽  
Milky Way ◽  
Galactic Center ◽  
Interstellar Extinction ◽  
Intermediate Band ◽  
Stellar Cluster ◽  
Density Peaks ◽  
Mass Segregation ◽  
Sgr A ◽  
Number Counts

AbstractHigh-resolution adaptive optics observations of the inner 0.5 pc of the Milky Way with multiple intermediate band filters are presented. From the images, stellar number counts and a detailed map of the interstellar extinction were extracted. The extinction map is consistent with a putative southwest-northeast aligned outflow from the central arcseconds.An azimuthally averaged, crowding and extinction corrected stellar density profile presents clear evidence for the existence of a stellar cusp around Sgr A*. Several density peaks are found in the cluster that may indicate clumping of stars, possibly related to the last epoch of star formation in the Galactic Center. An analysis of stars in the brightness range 14.25 < magK < 15.75 shows possible signs of mass segregation.

scholarly journals A Statistical Estimation of the Occurrence of Extraterrestrial Intelligence in the Milky Way Galaxy

Galaxies ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 5
Author(s):  
Xiang Cai ◽  
Jonathan H. Jiang ◽  
Kristen A. Fahy ◽  
Yuk L. Yung
Keyword(s):  
Statistical Estimation ◽  
Milky Way ◽  
Galactic Center ◽  
Model Simulation ◽  
Temporal Variations ◽  
Extraterrestrial Intelligence ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Peak Location ◽  
Intelligent Life

In the field of astrobiology, the precise location, prevalence, and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial–temporal variations and the prevalence of potential ETI within the Galaxy. This model estimates the occurrence of ETI, providing guidance on where to look for intelligent life in the Search for ETI (SETI) with a set of criteria, including well-established astrophysical properties of the Milky Way. Further, typically overlooked factors such as the process of abiogenesis, different evolutionary timescales, and potential self-annihilation are incorporated to explore the growth propensity of ETI. We examine three major parameters: (1) the likelihood rate of abiogenesis (λA); (2) evolutionary timescales (Tevo); and (3) probability of self-annihilation of complex life (Pann). We found Pann to be the most influential parameter determining the quantity and age of galactic intelligent life. Our model simulation also identified a peak location for ETI at an annular region approximately 4 kpc from the galactic center around 8 billion years (Gyrs), with complex life decreasing temporally and spatially from the peak point, asserting a high likelihood of intelligent life in the galactic inner disk. The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult.

scholarly journals Integrated spectroscopy of extragalactic Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 155-160
Author(s):  
Charli M. Sakari
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Light Element ◽  
Element Abundance ◽  
Future Perspectives ◽  
Host Galaxies ◽  
Chemical Abundances ◽  
Essential Information ◽  
Light Element Abundance ◽  
Detailed Chemical

AbstractIntegrated light (IL) spectroscopy enables studies of stellar populations beyond the Milky Way and its nearest satellites. In this paper, I will review how IL spectroscopy reveals essential information about globular clusters and the assembly histories of their host galaxies, concentrating particularly on the metallicities and detailed chemical abundances of the GCs in M31. I will also briefly mention the effects of multiple populations on IL spectra, and how observations of distant globular clusters help constrain the source(s) of light-element abundance variations. I will end with future perspectives, emphasizing how IL spectroscopy can bridge the gap between Galactic and extragalactic astronomy.

scholarly journals An Overview of the Globular Cluster System of the Galaxy

1988 ◽  
Vol 126 ◽  
pp. 37-48
Author(s):  
Robert Zinn
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cluster System ◽  
Open Clusters ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Harlow Shapley

Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.

scholarly journals Did the Bulge Form All at Once?

1996 ◽  
Vol 169 ◽  
pp. 403-410
Author(s):  
R.M. Rich
Keyword(s):  
Galaxy Evolution ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Field Population ◽  
Dynamical Instability ◽  
Galactic Bulge ◽  
Recent Developments ◽  
Order Of Magnitude ◽  
History Of

It is reasonable to say that if Jan Oort were alive today, he would no doubt find recent developments in the study of the Galactic bulge to be fascinating. Oort considered the Galactic bulge in two contexts. First, he was interested in the use of the RR Lyrae stars as probes to determine the distance to the Galactic Center. No doubt, Oort would have been excited about the growing evidence of the bulge's triaxiality, as well as by the debate over the age of the bulge. His second interest was in the nature of activity at the center, an issue that I will not discuss in this review. The latter also remains an unsolved problem of the Milky Way, and (based on his work) one that might have been nearer to his heart than this one. Yet the question of when the bulge formed is ultimately a question about the formation history of the Galaxy. The oldest stars (those whose ages we are certain of) are found in Galactic globular clusters, the sum total of which are ≈ 5 × 107M⊙. The field population of the bulge is ≈ 2–3 × 1010M⊙, an order of magnitude more massive than the field population of the metal poor spheroid. So if the bulge formed all at once, and early, then the Milky Way had a luminous, even cataclysmic youth. But if the bulge formed later in the history of our galaxy, as a starburst or dynamical instability of the central disk, then the young Milky Way may have been inconspicuous and primeval galaxies may be hard to find indeed. If our bulge formed very early, its stellar population might have much in common with the giant ellipticals, while a late bulge might teach us much about processes that affect galaxy evolution.

scholarly journals Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations

2020 ◽  
Vol 498 (2) ◽  
pp. 2472-2491 ◽  
Author(s):  
J M Diederik Kruijssen ◽  
Joel L Pfeffer ◽  
Mélanie Chevance ◽  
Ana Bonaca ◽  
Sebastian Trujillo-Gomez ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Mass Range ◽  
Stellar Mass ◽  
Host Galaxies ◽  
Stellar Halo ◽  
Major Merger ◽  
Virial Mass ◽  
Minor Mergers ◽  
Stellar Masses

ABSTRACT Globular clusters (GCs) formed when the Milky Way experienced a phase of rapid assembly. We use the wealth of information contained in the Galactic GC population to quantify the properties of the satellite galaxies from which the Milky Way assembled. To achieve this, we train an artificial neural network on the E-MOSAICS cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies. The network uses the ages, metallicities, and orbital properties of GCs that formed in the same progenitor galaxies to predict the stellar masses and accretion redshifts of these progenitors. We apply the network to Galactic GCs associated with five progenitors: Gaia-Enceladus, the Helmi streams, Sequoia, Sagittarius, and the recently discovered ‘low-energy’ GCs, which provide an excellent match to the predicted properties of the enigmatic galaxy ‘Kraken’. The five galaxies cover a narrow stellar mass range [M⋆ = (0.6–4.6) × 108 M⊙], but have widely different accretion redshifts ($\mbox{$z_{\rm acc}$}=0.57\!-\!2.65$). All accretion events represent minor mergers, but Kraken likely represents the most major merger ever experienced by the Milky Way, with stellar and virial mass ratios of $\mbox{$r_{M_\star }$}=1$:$31^{+34}_{-16}$ and $\mbox{$r_{M_{\rm h}}$}=1$:$7^{+4}_{-2}$, respectively. The progenitors match the z = 0 relation between GC number and halo virial mass, but have elevated specific frequencies, suggesting an evolution with redshift. Even though these progenitors likely were the Milky Way’s most massive accretion events, they contributed a total mass of only log (M⋆, tot/M⊙) = 9.0 ± 0.1, similar to the stellar halo. This implies that the Milky Way grew its stellar mass mostly by in-situ star formation. We conclude by organizing these accretion events into the most detailed reconstruction to date of the Milky Way’s merger tree.

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