scholarly journals Mass of the Milky Way

2004 ◽  
Vol 220 ◽  
pp. 213-214
Author(s):  
O. I. Wong ◽  
M. J. Drinkwater ◽  
J. B. Jones ◽  
M. D. Gregg ◽  
K. C. Freeman
Keyword(s):  
Milky Way ◽  
Galactic Centre ◽  
Escape Velocity ◽  
The Galaxy

We present a new estimate of the mass of the Milky Way based on the escape velocity of a sample of distant stars, about 12 kpc from the Galactic centre and about 5 kpc from the plane of the Galaxy. Our sample is very different from previous escape-velocity studies, being compiled from an all-object spectroscopic survey of a region of sky. the derived mass within 12 kpc of the Galactic centre is (1.3 ±0.3) × 1011M⊙.

scholarly journals The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way

2018 ◽  
Vol 616 ◽  
pp. L9 ◽  
Author(s):  
G. Monari ◽  
B. Famaey ◽  
I. Carrillo ◽  
T. Piffl ◽  
M. Steinmetz ◽  
...  
Keyword(s):  
Mass Concentration ◽  
Milky Way ◽  
Galactic Centre ◽  
High Concentration ◽  
Circular Velocity ◽  
Halo Stars ◽  
Dark Matter Mass ◽  
The Galaxy ◽  
Escape Speed ◽  
Gaia Dr2

We measure the escape speed curve of the Milky Way based on the analysis of the velocity distribution of ~2850 counter-rotating halo stars from the Gaia Data Release 2. The distances were estimated through the StarHorse code, and only stars with distance errors smaller than 10% were used in the study. The escape speed curve is measured at Galactocentric radii ranging from ~5 kpc to ~10.5 kpc. The local Galactic escape at the Sun’s position is estimated to be ve(r⊙) = 580 ± 63 km s−1, and it rises towards the Galactic centre. Defined as the minimum speed required to reach three virial radii, our estimate of the escape speed as a function of radius implies for a Navarro–Frenk–White profile and local circular velocity of 240 km s−1 a dark matter mass M200 = 1.28−0.50+0.68 × 1012 M⊙ and a high concentration c200 = 11.09−1.79+2.94. Assuming the mass-concentration relation of ΛCDM, we obtain M200 = 1.55−0.51+0.64 × 1012 M⊙ and c200 = 7.93−0.27+0.33 for a local circular velocity of 228 km s−1.

scholarly journals Gaia DR2 in 6D: searching for the fastest stars in the Galaxy

2018 ◽  
Vol 490 (1) ◽  
pp. 157-171 ◽  
Author(s):  
T Marchetti ◽  
E M Rossi ◽  
A G A Brown
Keyword(s):  
Milky Way ◽  
Small Sample Size ◽  
European Space Agency ◽  
Small Sample ◽  
Radial Velocities ◽  
Orbital Parameter ◽  
Galactic Centre ◽  
Space Agency ◽  
The Galaxy ◽  
Orbit Integration

ABSTRACT We search for the fastest stars in the subset of stars with radial velocity measurements of the second data release (DR2) of the European Space Agency mission Gaia. Starting from the observed positions, parallaxes, proper motions, and radial velocities, we construct the distance and total velocity distribution of more than 7 million stars in our Milky Way, deriving the full 6D phase space information in Galactocentric coordinates. These information are shared in a catalogue, publicly available at http://home.strw.leidenuniv.nl/~marchetti/research.html. To search for unbound stars, we then focus on stars with a probability greater than $50 $ per cent of being unbound from the Milky Way. This cut results in a clean sample of 125 sources with reliable astrometric parameters and radial velocities. Of these, 20 stars have probabilities greater than 80 per cent of being unbound from the Galaxy. On this latter subsample, we perform orbit integration to characterize the stars’ orbital parameter distributions. As expected given the relatively small sample size of bright stars, we find no hypervelocity star candidates, stars that are moving on orbits consistent with coming from the Galactic Centre. Instead, we find seven hyperrunaway star candidates, coming from the Galactic disc. Surprisingly, the remaining 13 unbound stars cannot be traced back to the Galaxy, including two of the fastest stars (around 700 km s−1). If conformed, these may constitute the tip of the iceberg of a large extragalactic population or the extreme velocity tail of stellar streams.

scholarly journals 3D N-Body Simulations of the Milky Way

1996 ◽  
Vol 169 ◽  
pp. 125-131 ◽  
Author(s):  
R. Fux ◽  
L. Martinet ◽  
D. Pfenniger
Keyword(s):  
Milky Way ◽  
Position Angle ◽  
Angular Speed ◽  
Galactic Centre ◽  
Mass Model ◽  
Axis Ratio ◽  
Ongoing Work ◽  
The Galaxy ◽  
Kinematical Data ◽  
Extension Axis

While the existence of a central bar in our Galaxy now seems to be well established, its parameters (such as position angle, extension, axis ratio, angular speed etc…) still remain controversial. The large amount of photometrical and stellar kinematical data becoming now available within ∼ 30° of the Galactic Centre should provide potentially new constraints on these parameters. Unfortunately, a detailed barred model of the Milky Way, which would offer a powerful work frame to interpret such observations, does not exist yet. We therefore report here on a first attempt at constructing a 3D dynamically self-consistent barred model of the Galaxy. The idea is to follow the time evolution of a set of 400,000 particles initially distributed according to a plausible axisymmetric mass model of the Milky Way and in virial equilibrium, hoping that a bar will form spontaneously. Gas is not included so far, but will be introduced as a next step in this ongoing work. Some results presented at this meeting will be only quickly summarised here and explained in some more details elsewhere (Fux et al. 1995 and A&A paper in preparation).

scholarly journals An Estimate of the Dark-Matter Content in the Galaxy

1995 ◽  
Vol 164 ◽  
pp. 394-394
Author(s):  
Slobodan Ninković
Keyword(s):  
Dark Matter ◽  
Total Mass ◽  
Milky Way ◽  
Local Group ◽  
Matter Content ◽  
Escape Velocity ◽  
The Galaxy

The total mass of the Milky-Way dark corona and its contribution to the total mass of the Galaxy, is estimated by combining the limits imposed by the Local Group as probably bound and the constraints on the local escape velocity. The results: total mass of the Milky Way about 1.6 TM⊙ (dark corona over 1.5 TM⊙; T = 1012), local escape velocity about 600 kms−1.

scholarly journals Using the Milky Way as a template for understanding star formation in extreme environments across cosmological timescales

2012 ◽  
Vol 8 (S292) ◽  
pp. 333-333
Author(s):  
Steven N. Longmore
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Formation Rate ◽  
Volume Density ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Dense Gas ◽  
Star Forming ◽  
Star Formation Activity ◽  
The Galaxy

AbstractRecent surface- and volume-density star formation relations have been proposed which potentially unify our understanding of how gas is converted into stars, from the nearest star forming regions to ultra-luminous infrared galaxies. The inner 500 pc of our Galaxy – the Central Molecular Zone – contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of these star-formation prescriptions can be tested.We have used recently-available data from HOPS, MALT90 and HiGAL at wavelengths where the Galaxy is transparent, to find the dense, star-forming molecular gas across the Milky Way [Longmore et al. (2012a), Longmore et al. (2012b)]. We use water and methanol maser emission to trace star formation activity within the last 105 years and 30 GHz radio continuum emission from the Wilkinson Microwave Anisotropy Satellite (WMAP) to estimate the high-mass star formation rate averaged over the last ∼ 4 × 106 years.We find the dense gas distribution is dominated by the very bright and spatially-extended emission within a few degrees of the Galactic centre [Purcell et al. (2012)]. This region accounts for ∼80% of the NH3(1,1) integrated intensity but only contains 4% of the survey area. However, in stark contrast, the distribution of star formation activity tracers is relatively uniform across the Galaxy.To probe the dense gas vs SFR relationship towards the Galactic centre region more quantitatively, we compared the HiGAL column density maps to the WMAP-derived SFR across the same region. The total mass and SFR derived using these methods agree well with previous values in the literature. The main conclusion from this analysis is that both the column-density threshold and volumetric SF relations over-predict the SFR by an order of magnitude given the reservoir of dense gas available to form stars. The region 1° < l < 3.5°, |b| < 0.5° is particular striking in this regard. It contains ∼107 M⊙ of dense molecular gas — enough to form 1000 Orion-like clusters — but the present-day star formation rate within this gas is only equivalent to that in Orion. This implication of this result is that any universal column/volume density relations must be a necessary but not sufficient condition for SF to occur.Understanding why such large reservoirs of dense gas deviate from commonly assumed SF relations is of fundamental importance and may help in the quest to understand SF in more extreme (dense) environments, like those found in interacting galaxies and at earlier epochs of the Universe.

The galactic habitable zone in barred galaxies

2006 ◽  
Vol 5 (4) ◽  
pp. 325-326 ◽  
Author(s):  
M. Sundin
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Habitable Zone ◽  
Escape Velocity ◽  
Stellar Orbits ◽  
Barred Galaxies ◽  
The Galaxy ◽  
Pattern Speed ◽  
Disc Galaxies ◽  
High Metallicity

One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to define since the bar can change stellar orbits. Many disc galaxies, including the Milky Way, are barred galaxies. The stars in the bar move in a number of fairly complicated orbits. However, the bar will also influence the orbits of stars in the whole galaxy. Stars passing close to the bar can either gain or lose angular momentum, due to a positive or negative torque by the bar. Some stars will therefore be captured by the bar while some stars eventually may reach the escape velocity from the galaxy. The bar will hence be able to relocate stars, and stars with low or high metallicity could be found far away from their original orbits. The ordinary evolution of a bar is to grow in length out to the co-rotation radius for the pattern speed of the bar. As the galaxy ages, and the bar grows in length, the bar will influence a larger part of the galaxy. The effect of moving stars inwards or outwards is greatest just outside the bar, and this region can eventually lose a high percentage of the stars.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

The Long View of Planetary Systems

2018 ◽  
Author(s):  
Karel Schrijver
Keyword(s):  
Solar System ◽  
Milky Way ◽  
Planetary Systems ◽  
Giant Planets ◽  
Milky Way Galaxy ◽  
Population Statistics ◽  
The Past ◽  
General Terms ◽  
The Galaxy ◽  
The Universe

How many planetary systems formed before our’s did, and how many will form after? How old is the average exoplanet in the Galaxy? When did the earliest planets start forming? How different are the ages of terrestrial and giant planets? And, ultimately, what will the fate be of our Solar System, of the Milky Way Galaxy, and of the Universe around us? We cannot know the fate of individual exoplanets with great certainty, but based on population statistics this chapter sketches the past, present, and future of exoworlds and of our Earth in general terms.

scholarly journals The globular cluster system of the Auriga simulations

2020 ◽  
Vol 496 (1) ◽  
pp. 638-648 ◽  
Author(s):  
Timo L R Halbesma ◽  
Robert J J Grand ◽  
Facundo A Gómez ◽  
Federico Marinacci ◽  
Rüdiger Pakmor ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Milky Way ◽  
Cluster Formation ◽  
Solar Radius ◽  
High Mass ◽  
Formation Model ◽  
The Galaxy ◽  
High Mass Loss ◽  
Globular Cluster System ◽  
Varying Mass

ABSTRACT We investigate whether the galaxy and star formation model used for the Auriga simulations can produce a realistic globular cluster (GC) population. We compare statistics of GC candidate star particles in the Auriga haloes with catalogues of the Milky Way (MW) and Andromeda (M31) GC populations. We find that the Auriga simulations do produce sufficient stellar mass for GC candidates at radii and metallicities that are typical for the MW GC system (GCS). We also find varying mass ratios of the simulated GC candidates relative to the observed mass in the MW and M31 GCSs for different bins of galactocentric radius metallicity (rgal–[Fe/H]). Overall, the Auriga simulations produce GC candidates with higher metallicities than the MW and M31 GCS and they are found at larger radii than observed. The Auriga simulations would require bound cluster formation efficiencies higher than 10 per cent for the metal-poor GC candidates, and those within the Solar radius should experience negligible destruction rates to be consistent with observations. GC candidates in the outer halo, on the other hand, should either have low formation efficiencies, or experience high mass-loss for the Auriga simulations to produce a GCS that is consistent with that of the MW or M31. Finally, the scatter in the metallicity as well as in the radial distribution between different Auriga runs is considerably smaller than the differences between that of the MW and M31 GCSs. The Auriga model is unlikely to give rise to a GCS that can be consistent with both galaxies.

USE OF THE GALAXY AS A TOOL FOR SPATIAL AND TEMPORAL ORIENTATION DURING THE EARLY ISLAMIC PERIOD AND UP TO THE 15TH CENTURY

2021 ◽  
Vol 31 (1) ◽  
pp. 1-44
Author(s):  
Andreas Eckart
Keyword(s):  
Milky Way ◽  
The Other ◽  
Temporal Orientation ◽  
Islamic Period ◽  
Space And Time ◽  
15Th Century ◽  
Other Hand ◽  
The Galaxy ◽  
Early Islamic Period ◽  
Early Islamic

AbstractWe study to what extent the Milky Way was used as an orientation tool at the beginning of the Islamic period covering the 8th to the 15th century, with a focus on the first half of that era. We compare the texts of three authors from three different periods and give detailed comments on their astronomical and traditional content. The text of al-Marzūqī summarises the information on the Milky Way put forward by the astronomer and geographer ʾAbū Ḥanīfa al-Dīnawarī. The text makes it clear that in some areas the Milky Way could be used as a geographical guide to determine the approximate direction toward a region on Earth or the direction of prayer. In the 15th century, the famous navigator Aḥmad b. Māǧid describes the Milky Way in his nautical instructions. He frequently demonstrates that the Milky Way serves as a guidance aid to find constellations and stars that are useful for precise navigation on land and at sea. On the other hand, Ibn Qutayba quotes in his description of the Milky Way a saying from the famous Bedouin poet Ḏū al-Rumma, which is also mentioned by al-Marzūqī. In this saying the Milky Way is used to indicate the hot summer times in which travelling the desert was particularly difficult. Hence, the Milky Way was useful for orientation in space and time and was used for agricultural and navigational purposes.

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