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TOPIC: Milky Way
Blobrana


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RE: Milky Way
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When Galaxies Collide, our Solar System Will Go for a Ride
For decades, astronomers have known that the Milky Way galaxy is on a collision course with the neighbouring Andromeda spiral galaxy. What was unknown until now: the fate of the Sun and our solar system in that melee. New calculations by theorists T.J. Cox and Avi Loeb (Harvard-Smithsonian Centre for Astrophysics) show that the Sun and its planets will be exiled to the outer reaches of the merged galaxy. Moreover, the collision will take place within the Sun's lifetime, before it becomes a burned-out white dwarf star.

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Blobrana


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Title: The Collision Between The Milky Way And Andromeda
Authors: T. J. Cox and Abraham Loeb

We use an Nbody/hydrodynamic simulation to forecast the future encounter between the Milky Way and the Andromeda galaxies, given current observational constraints on their relative distance, relative velocity, and masses. Allowing for a comparable amount of diffuse mass to fill the volume of the Local Group, we find that the two galaxies are likely to collide in a few billion years - within the Suns lifetime. During the first close encounter of the two galaxies, there is a 12% chance that the Sun will be pulled from its present position and reside in the extended tidal material. After the second close encounter, there is a 30% chance that the Sun will reside in the extended tidal material, and a 2.7% chance that our Sun will be more tightly bound to Andromeda than to the Milky Way. Eventually, after the merger has completed, the Sun is likely to be scattered to the outer halo and reside at much larger radii (> 30 kpc). The density profiles of the stars, gas and dark matter in the merger product resemble those of elliptical galaxies. Our Local Group model therefore provides a prototype progenitor of lateforming elliptical galaxies.



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Blobrana


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Posts: 131433
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Milky Way Collision
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Astronomers have run new simulations to see what could happen when an expected collision takes place between our galaxy and another big one - possibly within our descendants lifetimes.
The surprising results: little of the celestial fireworks that were widely expected to occur as great gas clouds crunch together to form new stars. In­stead, a more outlandish possibility arose.
 The computer simulations indicated there is a one in 37 chance well end up living in that other galaxy - majestic Andromeda, said the researchers, T. J. Cox and Abraham Loeb of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Mass.

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If Homo sapiens can stick it out on Earth for another two billion years, our descendants may witness quite a show in the night sky. Researchers estimate that the Milky Way will collide with its nearest neighbour, the Andromeda galaxy, at around that timewell before the sun collapses into a white dwarf.
This close encounter of the galactic kind could easily kick our solar system to the farthest reaches of the galaxy, and there is a small chance we might even take up residence in Andromeda, according to astronomers T. J. Cox and Abraham Loeb of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Mass.

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Blobrana


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Posts: 131433
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RE: Milky Way
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Title: First proper motions of thin dust filaments at the Galactic Center
Authors: K. Muzic, A. Eckart, R. Schoedel, L. Meyer, A. Zensus

Context: L'-band (3.8 micron) images of the Galactic Centre show a large number of thin filaments in the mini-spiral, located west of the mini-cavity and along the inner edge of the Northern Arm. One possible mechanism that could produce such structures is the interaction of a central wind with the mini-spiral. Additionally, we identify similar features that appear to be associated with stars. Aims: We present the first proper motion measurements of the thin dust filaments observed in the central parsec around SgrA* and investigate possible mechanisms that could be responsible for the observed motions. Methods: The observations have been carried out using the NACO adaptive optics system at the ESO VLT. The images have been transformed to a common coordinate system and features of interest were extracted. Then a cross-correlation technique could be performed in order to determine the offsets between the features with respect to their position in the reference epoch. Results: We derive the proper motions of a number of filaments and 2 cometary shaped dusty sources close (in projection) to SgrA*. We show that the shape and the motion of the filaments does not agree with a purely Keplerian motion of the gas in the potential of the supermassive black hole at the position of SgrA*. Therefore, additional mechanisms must be responsible for their formation and motion. We argue that the properties of the filaments are probably related to an outflow from the disk of young mass-losing stars around SgrA*. In part, the outflow may originate from the black hole itself. We also present some evidence and theoretical considerations that the outflow may be collimated.

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Blobrana


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Serpens Interstellar Clouds
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Title: The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds VIII. Serpens Observed with MIPS
Authors: Paul M. Harvey, Luisa M. Rebull, Tim Brooke, William J. Spiesman, Nicholas Chapman, Tracy L. Huard, Neal J. Evans II, Lucas Cieza, Shih-Ping Lai, Lori E. Allen, Lee G. Mundy, Deborah L. Padgett, Anneila I. Sargent, Karl R. Stapelfeldt, Philip C. Myers, Ewine F. van Dishoeck, Geoffrey A. Blake, David W. Koerner

We present maps of 1.5 square degrees of the Serpens dark cloud at 24, 70, and 160µ observed with the Spitzer Space Telescope MIPS Camera. More than 2400 compact sources have been extracted at 24um, nearly 100 at 70um, and 4 at 160um. We estimate completeness limits for our 24um survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colours, and magnitudes in the Serpens cloud to two reference data sets, a 0.50 deg² set on a low-extinction region near the dark cloud, and a 5.3 deg² subset of the SWIRE ELAIS N1 data that was processed through our pipeline. These results show that there is an easily identifiable population of young stellar object candidates in the Serpens Cloud that is not present in either of the reference data sets. We also show a comparison of visual extinction and cool dust emission illustrating a close correlation between the two, and find that the most embedded YSO candidates are located in the areas of highest visual extinction.

arXiv:0704.0253v1 (228kb, PDF)

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Blobrana


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Posts: 131433
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Serpens star-forming region
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Title: The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. IX. The Serpens YSO Population As Observed With IRAC and MIPS
Authors: Paul Harvey, Bruno Merin, Tracy L. Huard, Luisa M. Rebull, Nicholas Chapman, Neal J. Evans II, Philip C. Myers

We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy observations of the Serpens star-forming region. In particular we present a set of criteria for isolating bona fide young stellar objects, YSO's, from the extensive background contamination by extra-galactic objects. We then discuss the properties of the resulting high confidence set of YSO's. We find 235 such objects in the 0.85 deg^2 field that was covered with both IRAC and MIPS. An additional set of 51 lower confidence YSO's outside this area is identified from the MIPS data combined with 2MASS photometry. We describe two sets of results, colour-colour diagrams to compare our observed source properties with those of theoretical models for star/disk/envelope systems and our own modelling of the subset of our objects that appear to be star+disks. These objects exhibit a very wide range of disk properties, from many that can be fit with actively accreting disks to some with both passive disks and even possibly debris disks. We find that the luminosity function of YSO's in Serpens extends down to at least a few x .001 Lsun or lower for an assumed distance of 260 pc. The lower limit may be set by our inability to distinguish YSO's from extra-galactic sources more than by the lack of YSO's at very low luminosities. A spatial clustering analysis shows that the nominally less-evolved YSO's are more highly clustered than the later stages and that the background extra-galactic population can be fit by the same two-point correlation function as seen in other extra-galactic studies. We also present a table of matches between several previous infrared and X-ray studies of the Serpens YSO population and our Spitzer data set.

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Blobrana


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Posts: 131433
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RE: Milky Way
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Chemical Composition of Stars in Clusters Can Tell History of our Galaxy
Using ESO's Very Large Telescope, an international team of astronomers has shown how to use the chemical composition of stars in clusters to shed light on the formation of our Milky Way. This discovery is a fundamental test for the development of a new chemical tagging technique uncovering the birth and growth of our Galactic cradle.
The formation and evolution of galaxies, and in particular of the Milky Way - the 'island universe' in which we live, is one of the major puzzles of astrophysics: indeed, a detailed physical scenario is still missing and its understanding requires the joint effort of observations, theories and complex numerical simulations. ESO astronomer Gayandhi De Silva and her colleagues used the Ultraviolet and Visual Echelle Spectrograph (UVES) on ESO's VLT to find new ways to address this fundamental riddle.

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Blobrana


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Posts: 131433
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IRAS06145+1455
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Title: A star cluster at the edge of the Galaxy
Authors: J. Brand, J.G.A. Wouterloot

We study stars and molecular gas in the direction of IRAS06145+1455 (WB89-789) through NIR (JHK), molecular line-, and dust continuum observations. The kinematic distance of the associated molecular cloud is 11.9 kpc. With a galactocentric distance of about 20.2 kpc, this object is at the edge of the (molecular) disk of the Galaxy. The near-IR data show the presence of an (embedded) cluster of about 60 stars, with a radius ca. 1.3 pc and an average stellar surface density of ca. 12 pc^{-2}. We find at least 14 stars with NIR-excess, 3 of which are possibly Class I objects. The cluster is embedded in a 1000 Mo molecular/dust core, from which a molecular outflow originates. The temperature of most of the outflowing gas is < 40 K, and the total mass of the swept-up material is < 10 Mo. Near the centre of the flow, indications of much higher temperatures are found, probably due to shocks. A spectrum of one of the probable cluster members shows a tentative likeness to that of a K3III-star (with an age of at least 20 Myr). If correct, this would confirm the kinematic distance. This cluster is the furthest one from the Galactic center yet detected. The combination of old and recent activity implies that star formation has been going on for at least 20 Myr, which is difficult to understand considering the location of this object, where external triggers are either absent or weak, compared to the inner Galaxy. This suggests that once star formation is occurring, later generations of stars may form through the effect of the first generation of stars on the (remnants of) the original molecular cloud.

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Blobrana


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VI. Perseus Interstellar Cloud
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Title: The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VI. Perseus Observed with MIPS
Authors: L. M. Rebull, K. R. Stapelfeldt, N. J. Evans II, J. K. Joergensen, P. M. Harvey, T. Y. Brooke, T. L. Bourke, D. L. Padgett, N. L. Chapman, S.-P. Lai, W. J. Spiesmann, A. Noreiga-Crespo, B. Merin, T. Huard, L. E. Allen, G. A. Blake, T. Jarrett, D. W. Koerner, L. G. Mundy, P. C. Myers, A. I. Sargent, E. F. van Dishoeck, Z. Wahhaj, K. E. Young

We present observations of 10.6 square degrees of the Perseus molecular cloud at 24, 70, and 160 microns with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). The image mosaics show prominent, complex extended emission dominated by illuminating B stars on the East side of the cloud, and by cold filaments of 160 micron emission on the West side. Of 3950 point sources identified at 24 microns, 1141 have 2MASS counterparts. A quarter of these populate regions of the Ks vs. Ks-[24] diagram that are distinct from stellar photospheres and background galaxies, and thus are likely to be cloud members with infrared excess. Nearly half (46%) of these 24 micron excess sources are distributed outside the IC 348 and NGC 1333 clusters. NGC 1333 shows the highest fraction of stars with flat or rising spectral energy distributions (28%), while Class II SEDs are most common in IC 348. These results are consistent with previous relative age determinations for the two clusters.
The intercluster region contains several tightly clumped (r~0.1 pc) young stellar aggregates whose members exhibit a wide variety of infrared spectral energy distributions characteristic of different circumstellar environments. One possible explanation is a significant age spread among the aggregate members, such that some have had time to evolve more than others. Alternatively, if the aggregate members all formed at roughly the same time, then remarkably rapid circumstellar evolution would be required to account for the association of Class I and Class III sources at ages <~1 Myr.
We highlight important results for several other objects as well.

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Blobrana


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W3
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W3 is a region where many massive stars are forming in a string of stellar clusters, located about 6,000 light years from Earth in the Perseus arm of the Milky Way galaxy. W3 is part of a vast molecular cloud complex that also contains the W4 superbubble (not seen in this image). Scientists believe that the extraordinary amount of star formation in W3 has possibly been influenced by neighbouring W4, an inflating bubble of gas over 100 light years across. W4 may directly trigger the birth of W3's massive stellar clusters as it expands and sweeps up molecular gas into a high-density layer at its edge, within which stars can form. Another possible scenario is that W4's expansion has caused a domino effect of star formation, forming the cluster IC 1795 (seen as a clump of X-ray sources in the bottom left corner of this image) which in turn triggered formation of the young, massive clusters in W3.

w3
Credit: X-ray: NASA/CXC/Penn State/L.Townsley et al.; Optical: Pal Obs. DSS

Position(2000): RA 02h 25m 40.60s | Dec +62ş 05' 52.40

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