Milky Way - Astronomy News

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Posts: 131433

Date: Dec 12 18:06 2006

RE: Milky Way	Permalink

University of California-Santa Barbara astronomers say their findings deepen the mystery about the missing stellar ancestors. "Many astronomers thought (the reason the stars have never been found) was because the stars without heavy elements were hidden from us. Because our galaxy formed from the inside out, the idea was that these very old stars would all be near the centre. But the centre of Milky Way is extremely crowded with dust and newer stars, making it very hard to detect individual old stars in this environment" - Evan Scannapieco of the university's Kavli Institute for Theoretical Physics and first author of the study. Source __________________

Blobrana

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Posts: 131433

Date: Dec 8 15:38 2006

Galactic First Stars	Permalink

Title: The Spatial Distribution of the Galactic First Stars I: High-Resolution N-body Approach Authors: Evan Scannapieco, Daisuke Kawata, Chris B. Brook, Raffaella Schneider, Andrea Ferrara, Brad K. Gibson We study the spatial distribution of Galactic metal-free stars by combining an extremely high-resolution (7.8 X 10^5 solar masses per particle) Cold Dark Matter N-body simulation of the Milky-Way with a semi-analytic model of metal enrichment. This approach allows us to resolve halos with virial temperatures down to the 10^4K atomic cooling limit, and it is sufficiently flexible to make a number of robust conclusions, despite the extremely uncertain properties of the first stars. Galactic metal-free stars are formed over a large redshift range, which peaks at z~10, but continues down to z~5, contributing stars at wide range of Galactocentric radii. Stars containing only metals generated by primordial stars are similarly widespread. Neither changing the efficiency of metal dispersal by two orders of magnitude, nor drastically changing the approximations in our semi-analytical model can affect these result. Thus, if they have sufficiently long lifetimes, a significant number of stars formed in initially primordial star clusters should be found in the nearby Galactic halo regardless of the specifics of metal-free star formation. Observations of metal abundances in Galactic halo stars should be taken as directly constraining the properties of primordial stars, and the lack of metal-free halo stars today should be taken as strongly suggesting a 0.8 solar mass lower limit on the primordial initial mass function. Read more (260kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Nov 22 11:25 2006

RE: Milky Way	Permalink

Title: Formation and evolution of the Galactic bulge: constraints from stellar abundances Authors: Silvia Ballero, Francesca Matteucci, Livia Origlia We present results for the chemical evolution of the Galactic bulge in the context of an inside-out formation model of the Galaxy. A supernova-driven wind was also included in analogy with elliptical galaxies. New observations of chemical abundance ratios and metallicity distribution have been employed in order to check the model results. We confirm previous findings that the bulge formed on a very short timescale with a quite high star formation efficiency and an initial mass function more skewed toward high masses than the one suitable for the solar neighbourhood. A certain amount of primary nitrogen from massive stars might be required to reproduce the nitrogen data at low and intermediate metallicities. Read more (25kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Nov 22 01:10 2006

Dark matter	Permalink

Our galaxy could be surrounded by a vast swarm of invisible companions. These giant clouds of dark matter – representing the failed seeds of galaxy formation – may be detected with a telescope to be launched next year. Dark matter makes up about 82% of all the matter in the universe, although nobody knows what it actually is. Small clouds of the stuff are thought to have coalesced after the big bang, and then gradually merged together. When enough dark matter is gathered into a huge "halo", it attracts ordinary gas to form stars, and so becomes a galaxy. Read more __________________

Blobrana

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Posts: 131433

Date: Nov 21 04:28 2006

RE: Milky Way	Permalink

Supercomputer study shows Milky Way's halo of dark matter in unprecedented detail Researchers at the University of California, Santa Cruz, have used NASA's most powerful supercomputer to run the largest simulation to date of the formation and evolution of the dark matter halo that envelopes the Milky Way galaxy. Their results show substructures within the halo in unprecedented detail, providing a valuable tool for understanding the evolutionary history of our galaxy. Source __________________

Blobrana

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Posts: 131433

Date: Oct 30 12:58 2006

Star Formation in Perseus	Permalink

Title: SK 1: A Possible Case of Triggered Star Formation in Perseus Authors: M. Rengel (1), K. Hodapp (2), J. Eisloeffel (3) ((1) Max Planck Institute for Solar System Research, (2) Institute for Astronomy, (3) Thueringer Landessternwarte Tautenburg) According to a triggered star formation scenario (e.g. Martin-Pintado & Cernicharo 1987) outflows powered by young stellar objects shape the molecular clouds, can dig cavities, and trigger new star formation. NGC 1333 is an active site of low- and intermediate star formation in Perseus and is a suggested site of self-regulated star formation Norman & Silk 1980. Therefore it is a suitable target for a study of triggered star formation (e.g. Sandell & Knee 2001, SK 1). On the other hand, continuum sub-mm observations of star forming regions can detect dust thermal emission of embedded sources (which drive outflows), and further detailed structures. Within the framework of our wide-field mapping of star formation regions in the Perseus and Orion molecular clouds using SCUBA at 850 and 450 micrometers, we map NCG 1333 with an area of around 14' x 21'. The maps show more structure than the previous maps of the region observed in sub-mm. We have unveiled the known embedded SK 1 source (in the dust shell of the SSV 13 ridge) and detailed structure of the region, among some other young protostars. In agreement with the SK 1 observations, our map of the region shows lumpy filaments and shells/cavities that seem to be created by outflows. The measured mass of SK 1 (~0.07 Msun) is much less than its virial mass (~0.2-1 Msun). Our observations support the idea of SK 1 as an event triggered by outflow-driven shells in NGC 1333 (induced by an increase in gas pressure and density due to radiation pressure from the stellar winds, that have presumably created the dust shell). This kind of evidences provides a more thorough understanding of the star formation regulation processes. Read more (224kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 27 13:17 2006

ISM in the Milky Way	Permalink

Title: Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: II. The Molecular Gas Disk Authors: Hiroyuki Nakanishi, Yoshiaki Sofue We created a three-dimensional distribution map of molecular gas throughout the Milky Way Galaxy using the latest ^12 CO(J=1-0) survey data cube and rotation curve based on the kinematic distance. The radial distribution of the molecular gas shows a central peak and a second peak around 0.5 R_0. The thickness of the molecular disk slightly increases from 48 pc to 160 pc with the galactocentric distance within a radius range of 0--11 kpc. We were able to trace the Outer, the Perseus, the Sagittarius-Carina, the Scutum-Crux, and the Norma arms as logarithmic spiral arms with pitch angles of 11° - 15°. Considering that the pitch angles of the spiral arms are within this range, the Norma and the Outer arms {seem to} be identified as the same spiral arm. We could also trace a midplane displacement, whose amplitude is nearly constant inside a 10 kpc radius and increases beyond this radius. The ridges of midplane displacement form leading spiral arms. Read more (509kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 25 01:36 2006

RE: Milky Way	Permalink

Credit: NASA/JPL-Caltech The C2d Legacy Project captured this image of stars forming in a cosmic cloud in Perseus. __________________

Blobrana

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Posts: 131433

Date: Oct 25 01:32 2006

What would a universe without stars look like?	Permalink

Besides cold and dark, it would also look relatively empty and lifeless, as chemical elements like carbon, nitrogen, oxygen, and most others which are necessary to create planets and sustain life wouldn't exist. Almost all chemical elements other than hydrogen and helium are born inside stars and spread across the universe when stars die. Despite their importance, much about the birth and early life of stars remains a mystery. That's why a team of astronomers on a Spitzer Legacy project called "From Molecular Cores to Planet-Forming Disks," abbreviated "c2d," are pointing all three instruments aboard NASA's Spitzer Space Telescope toward young stars forming in a variety of nearby cosmic clouds. Read more __________________

Blobrana

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Posts: 131433

Date: Oct 16 10:57 2006

Perseus Molecular Cloud	Permalink

Title: Current Star Formation in the Perseus Molecular Cloud: Constraints from Unbiased Submillimeter and Mid-Infrared Surveys Authors: Jes K. Jorgensen (1), Doug Johnstone (2,3), Helen Kirk (3,2), Philip C. Myers (1) ((1) Harvard-Smithsonian Centre for Astrophysics, (2) Herzberg Institute of Astrophysics, (3) University of Victoria) We present a census of the population of deeply embedded young stellar objects (YSOs) in the Perseus molecular cloud complex based on a combination of Spitzer Space Telescope mid-IR data from the c2d legacy team and JCMT/SCUBA submillimeter maps from the COMPLETE team. The mid-IR sources detected at 24 micron and having (3.6)-(4.5) > 1 are located close to the centre of the SCUBA cores, typically within 15" of their peaks. The narrowness of the spatial distribution of mid-IR sources around the peaks of the SCUBA cores suggests that no significant dispersal of the newly formed YSOs has occurred. This argues against the suggestion that motions of protostars regulate the time scales over which significant (Bondi-Hoyle) accretion can occur. The most deeply embedded YSOs are found in regions with high extinction, AV > 5, similar to the extinction threshold observed for the SCUBA cores. All the SCUBA cores with high concentrations have embedded YSOs, but not all cores with low concentrations are starless. An unbiased sample of 49 deeply embedded YSOs is constructed. Embedded YSOs are found in 40 of the 72 SCUBA cores with only three cores harbouring multiple embedded YSOs within 15". The equal number of SCUBA cores with and without embedded YSOs suggests that the time scale for the evolution through the dense prestellar stages, where the cores are recognized in the submillimeter maps and have central densities of 5e4-1e5 cm^-3, is similar to the time scale for the embedded protostellar stages. The current star formation efficiency of cores is estimated to be approximately 10-15%. In contrast, the star formation efficiency averaged over the cloud life time and compared to the total cloud mass is only a few percent, reflecting also the efficiency in assembling cloud material into the dense cores forming stars. Read more (121kb, PDF) __________________

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