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Origin of Milky Way's Hypothetical Dark Matter Signal May Not Be So Dark

A mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars - the incredibly dense, rapidly spinning cores of collapsed ancient stars that were up to 30 times more massive than the sun. That's the conclusion of a new analysis by an international team of astrophysicists, including researchers from the Department of Energy's SLAC National Accelerator Laboratory. The findings cast doubt on previous interpretations of the signal as a potential sign of dark matter - a form of matter that accounts for 85 percent of all matter in the universe but that so far has evaded detection.
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Scientists close in on the true mass of the Milky Way by calculating what they know, what they partially know and what is still uncertain

It's a problem of galactic complexity, but researchers are getting closer to accurately measuring the mass of the Milky Way Galaxy.
In the latest of a series of papers that could have broader implications for the field of astronomy, McMaster astrophysicist Gwendolyn Eadie, working with her PhD supervisor William Harris and with a Queen's University statistician, Aaron Springford, has refined Eadie and Harris's own method for measuring the mass of the galaxy that is home to our solar system.
The short answer, using the refined method, is between 4.0 X 10^11 and 5.8 X 10^11 solar masses. In simpler terms, that's about the mass of our Sun, multiplied by 400 to 580 billion. The Sun, for the record, has a mass of two nonillion (that's 2 followed by 30 zeroes) kilograms, or 330,000 times the mass of Earth. This Galactic mass estimate includes matter out to 125 kiloparsecs from the center of the Galaxy (125 kiloparsecs is almost 4 X 10^18 kilometers). When the mass estimate is extended out to 300kpc, the mass is approximately 9 X 10^11 solar masses.

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Title: Tracing the first stars and galaxies of the Milky Way
Author: Brendan F. Griffen, Gregory A. Dooley, Alexander P. Ji, Brian W. O'Shea, Facundo A. Gómez, Anna Frebel

We use 30 high-resolution dark matter halos of the Caterpillar simulation suite to probe the first stars and galaxies of Milky Way-mass systems. We quantify the environment of the high-z progenitors of the Milky Way and connect them to the properties of the host and satellites today. We identify the formation sites of the first generation of Population III (Pop III) stars (z ~ 25) and first galaxies (z ~ 22) with several different models based on a minimum halo mass including a simple model for Lyman-Werner feedback. Through this method we find approximately 23,000 ± 5,000 Pop III potentially star-forming sites per Milky Way-mass host, though this number is drastically reduced to ~550 star-forming sites when Lyman-Werner feedback is included, as it has critical effects at these length scales. The majority of these halos identified form in isolation (96% at z = 15) and are not subject to external enrichment by neighbouring halos (median separation ~1 pkpc at z = 15), though half merge with a system larger than themselves within 1.5 Gyrs. Approximately 55% of the entire population has merged into the host halo by z= 0. Using particle tagging, we additionally trace the Pop III remnant population to z = 0 and find an order of magnitude scatter in their number density at small (i.e. r < 5 kpc) and large (i.e. r > 50 kpc) galactocentric radii at z = 0. Using our large number of realizations, we provide fitting functions for determining the number of progenitor minihalo and atomic cooling halo systems that present-day dwarf galaxies and the Magellanic cloud system might have accreted since their formation. We demonstrate that observed dwarf galaxies with stellar masses below 10^4.6 solar masses are unlikely to have merged with any other star-forming systems.

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Title: The local spiral structure of the Milky Way
Author: Ye Xu, Mark Reid, Thomas Dame, Karl Menten, Nobuyuki Sakai, Jingjing Li, Andreas Brunthaler, Luca Moscadelli, Bo Zhang, Xingwu Zheng

The nature of the spiral structure of the Milky Way has long been debated. Only in the last decade have astronomers been able to accurately measure distances to a substantial number of high-mass star-forming regions, the classic tracers of spiral structure in galaxies. We report distance measurements at radio wavelengths using the Very Long Baseline Array for eight regions of massive star formation near the Local spiral arm of the Milky Way. Combined with previous measurements, these observations reveal that the Local Arm is larger than previously thought, and both its pitch angle and star formation rate are comparable to those of the Galaxy's major spiral arms, such as Sagittarius and Perseus. Toward the constellation Cygnus, sources in the Local Arm extend for a great distance along our line of sight and roughly along the solar orbit. Because of this orientation, these sources cluster both on the sky and in velocity to form the complex and long enigmatic Cygnus X region. We also identify a spur that branches between the Local and Sagittarius spiral arms.

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Largest ever 'age map' traces galactic history

Astronomers have measured the age of 70,000 stars across the Milky Way and put the results into a galactic map.
It confirms what was already suspected about our galaxy's growth: it started in the middle and grew outward.
This can be seen in the abundance of old stars near the centre of the disc.
Presented at the 227th meeting of the American Astronomical Society in Florida, it is the largest such map ever assembled.

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Title: Offset between stellar spiral arms and gas arms of the Milky Way
Author: L. G. Hou, J. L. Han

Spiral arms shown by different components may not be spatially coincident, which can constrain formation mechanisms of spiral structure in a galaxy. We reassess the spiral arm tangency directions in the Milky Way through identifying the bump features in the longitude plots of survey data for infrared stars, radio recombination lines (RRLs), star formation sites, CO, high density regions in clouds, and HI. The bump peaks are taken as indications for arm tangencies, which are close to the real density peaks near the spiral arm tangency point but often have ~ 1° offset to the interior of spiral arms. The arm tangencies identified from the longitudes plots for RRLs, HII regions, methanol masers, CO, high density gas regions, and HI gas appear nearly the same Galactic longitude, and therefore there is no obvious offset for spiral arms traced by different gas components. However, we find obvious displacements of 1.3° - 5.8° between gaseous bump peaks from the directions of the maximum density of old stars near the tangencies of the Scutum-Centaurus Arm, the northern part of the Near 3 kpc Arm, and maybe also the Sagittarius Arm. The offsets between the density peaks of gas and old stars for spiral arms are comparable with the arm widths, which is consistent with expectations for quasi-stationary density wave in our Galaxy.

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The tumultuous heart of our Galaxy

X-ray_view_of_the_Galactic_Centre_node_full_image_2.jpg

This new image of powerful remnants of dead stars and their mighty action on the surrounding gas from ESA's XMM-Newton X-ray observatory reveals some of the most intense processes taking place at the centre of our galaxy, the Milky Way.
The bright, point-like sources that stand out across the image trace binary stellar systems in which one of the stars has reached the end of its life, evolving into a compact and dense object - a neutron star or black hole. Because of their high densities, these compact remnants devour mass from their companion star, heating the material up and causing it to shine brightly in X-rays.

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Stars in Our Galaxy Move Far From Home

Scientists with the Sloan Digital Sky Survey (SDSS) have created a new map of the Milky Way and determined that 30 percent of stars have dramatically changed their orbits. This discovery, published in yesterday's issue of The Astrophysical Journal, brings a new understanding of how stars are formed, and how they travel throughout our galaxy.
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Herschel's hunt for filaments in the Milky Way

Observations with ESA's Herschel space observatory have revealed that our Galaxy is threaded with filamentary structures on every length scale. From nearby clouds hosting tangles of filaments a few light-years long to gigantic structures stretching hundreds of light-years across the Milky Way's spiral arms, they appear to be truly ubiquitous. The Herschel data have rekindled the interest of astronomers in studying filaments, emphasising the crucial role of these structures in the process of star formation.
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Milky Way's quiet life leaves it with no dark matter skeleton

Our galaxy has only ever merged with small galaxies, not large ones. This low-key history has left it bereft of dark matter from outside
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