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Topic: Galactic halo

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  Galactic Halo - Search Results - MSN Encarta
Halo, Galactic, roughly spherical area encompassing the luminous central disk of a galaxy.
The density of stars in the halo of a galaxy is much less...
The galactic halo is a huge sphere that surrounds the plane of the galaxy.
encarta.msn.com /Galactic_Halo.html   (128 words)

 galactic halo
The inner, visible part of the halo, which has roughly the same diameter as the galactic disk, is occupied by Population II objects, including globular clusters and old, individual stars.
Beyond this is a much larger region, called the dark halo or extended halo, containing large amounts of dark matter, the presence of which is revealed by its gravitational effect on the galaxy's rotation.
The nature of galactic dark matter is still undetermined but the most popular theory, supported by some recent observations, is that the dark halo is home to vast numbers of small, unseen bodies known as MACHOs.
www.daviddarling.info /encyclopedia/G/galhalo.html   (184 words)

 Spiral galaxy - Wikipedia, the free encyclopedia
Halo stars may be acquired from small galaxies which fall into and merge with the spiral galaxy—for example, the Sagittarius Dwarf Elliptical Galaxy is in the process of merging with the Milky Way and observations show that some stars in the halo of the Milky Way have been acquired from it.
Unlike the galactic disc, the halo seems to be free of dust, and in further contrast, stars in the galactic halo are of Population II, much older and with much lower metallicity than their Population I cousins in the galactic disc (but similar to those in the galactic bulge).
The motion of halo stars does bring them through the disc on occasion, and a number of small red dwarf stars close to the Sun are thought to belong to the galactic halo, for example Kapteyn's Star and Groombridge 1830.
en.wikipedia.org /wiki/Galactic_spheroid   (1125 words)

(The galactic halo should not be thought of as a shell, but rather as a roughly spherical volume of space within which globular clusters and some old stars are found.) While globulars are strongly concentrated toward the center of the Galaxy, some are found at very large distances from the galactic center.
Most globular clusters are in the extreme Population II or halo class, having stars metal-poor relative to the Sun by factors of at least 6 or 7 (and in most cases greater than 10), and being distributed essentially spherically about the galactic center.
Because of their importance in questions of galactic evolution and the study of the outer parts of the Galaxy, globular clusters continue to be investigated intensively by many astronomers today.
www.astro.bas.bg /galaxies/galaxies_files/stclust.html   (2118 words)

 STAR WARS: The Galaxy
The stellar density of the disk is greatest near the galactic centre (interpenetrating the bulge) and declines with both radial and vertical distance.
The halo is concentrated towards the galactic centre and tapers off to the limits of the galaxy's gravitational dominion, tens or hundreds of thousands of parsecs outside the disk.
The abundance of life in the Galactic Empire is harder to assess than the abundance of planets, since the range of preconditions for the origins and survival of life are not understood comprehensively.
www.theforce.net /swtc/galaxy.html   (8916 words)

 The Old Halo metallicity gradient: the trace of a self-enrichment process
Galactic globular clusters (hereafter GCs) are fossil records of the formation of the Galaxy.
Due to their high concentration near the galactic center, these metal-rich clusters, at least those located within the inner ~4 kpc of the Galaxy, are now thought to be associated with the galactic bulge rather than with the disk (Minnitt 1995, Côté 1999).
The stellar halo pattern is therefore consistent with the halo GC dichotomy.
vela.astro.ulg.ac.be /themes/stellar/halos/articles/halo3/halo3.html   (6945 words)

 03.22.2001 - Astronomers at UC Berkeley, Edinburgh, Cambridge, Vanderbilt report first direct detection of dark matter ...
Observations indicate that at most 35 percent of the galactic dark matter is made up of normal, so-called baryonic, matter - the stuff of stars and humans, composed of protons, neutrons and electrons.
The new population of white dwarfs in the halo "provides a natural explanation for the microlensing results," the team wrote in its paper.
Theories of galaxy and star formation will have to explain why the halo stars are overwhelmingly white dwarfs while the lower mass stars, which have not had enough time to evolve into white dwarfs, seem to be missing or are in abnormally small numbers.
www.berkeley.edu /news/media/releases/2001/03/22_halo.html   (1231 words)

 The Galactic Halo | Guide | Digital Universe | Hayden Planetarium
Unlike the population of the disk, where stars continue to form, the halo population is devoid of gas and dust and, therefore, star formation.
The main player in the Galactic halo is the system of globular clusters.
We place the radius of the halo at about 134,000 light-years (41 kpc); however, some astronomers believe it to be far larger, perhaps as much as 300,000 to 800,000 light-years in radius.
www.haydenplanetarium.org /universe/duguide/mwg_halo.php   (226 words)

 Exploring News & Features - Astronomical survey reveals that part of the "missing mass" of the galaxy ...
They calculate that if these dim stellar remnants are spread evenly throughout the galactic halo then they can account for at least 3 percent, and perhaps as much as 35 percent, of the dark matter in the galaxy.
If their analysis is correct, the galactic halo is filled with a vast population of these dim, dying stars, many of which must be between 10 billion and 13 billion years old, making them relics of the earliest days of the galaxy.
Previous studies have concluded that no more than 35 percent of the galactic dark matter is made up of normal, baryonic matterÑthe stuff of stars and humans, composed of protons, neutrons and electrons.
www.vanderbilt.edu /exploration_dev/news/news_dark.htm   (1213 words)

 Fossil structure in the galactic halo:
Stellar halos, which are a diffuse spheroidal component of galaxies, are thus a natural reservoir of the debris of past mergers.
However, it is not always possible to determine the energy of the stars in the Galactic halo, since it implies knowledge of the Galactic potential,as well as the 3D location and motion of the star.
The Spaghetti Project Survey (the analogy clearly is that the halo is a bowl of spaghetti!) is one of such projects that aims to identify fossil relics of destroyed galaxies.
www.europhysicsnews.com /full/16/article2/article2.html   (2138 words)

 Clouds Dominate the Galactic Halo
"The latest data confirm these results and show that instead of trailing away smoothly from the Galactic plane, a significant fraction of the hydrogen gas in the halo is concentrated in discrete clouds.
According to the researcher, the ubiquitous nature and dynamics of these newly discovered clouds support the theory that they are condensing out of the hot gas that is lifted into the halo through supernova explosions.
The results presented by Lockman suggest that, as some astronomers have predicted, the hot gas in the halo slowly cools and condenses into hydrogen clouds along with wispy filaments that connect them.
www.nrao.edu /pr/2003/honeclouds   (853 words)

Following the discovery by BATSE that the faint bursts are distributed isotropically on the sky, Galactic halo and corona models found new favor (see, e.g., Brainerd 1992, Li and Dermer 1992, Smith and Lamb 1993) as an attractive way of reconciling all of the evidence about gamma-ray bursts which favors Galactic neutron stars with isotropy.
The Galactic corona model predicts subtle anisotropies as a function of burst brightness, which are a signature of the model and may offer a means of verifying or rejecting it (Li, Duncan, and Thompson 1994; Podsiadlowski, Rees, and Ruderman 1995; Bulik and Lamb 1995).
Clearly, the cosmological and Galactic hypotheses are both consistent with the sky distribution and the brightness distribution of the BATSE bursts.
antwrp.gsfc.nasa.gov /diamond_jubilee/papers/lamb/node4.html   (874 words)

 SPACE.com -- Fog Lifts on Source of High-Speed Galactic Clouds
These high-velocity clouds move with rapidity in the galactic halo, a sparse sphere of objects that defines the outer reaches of our galaxy.
You'd also see other streams of stars in the halo, representing the remnants of smaller galaxies in various stages of being swallowed, moving at their own pace.
Researchers already know that fountains of hot gas flow away from the center of the Milky Way, pushed into the galactic halo by the ancient supernova explosions from whence they emanated or by the charged particles of stellar winds.
www.space.com /scienceastronomy/astronomy/galactic_clouds_991123.html   (1364 words)

 Galactic halo - Wikipedia, the free encyclopedia
The term galactic halo denotes a component of spiral galaxies, including our galaxy, the Milky Way, which extends further out than the disk, which is the most visible part of a spiral galaxy.
The galactic spheroid and the dark matter halo are concentrated towards the centre of their galaxy, and are roughly spherically symmetric.
In an elliptical galaxy, there is no sharp transition between the body of the galaxy and the halo.
en.wikipedia.org /wiki/Galactic_halo   (165 words)

 White Dwarf Halos
Besides, for the IMFs considered, the duration of the halo burst should be shorter than 1 Gyr in order to avoid too large a spread in the iron abundances of Population II halo dwarfs, and the predicted halo [O/Fe] ratio would be at odds with observations.
Galactic halos that are far too luminous (which should be seen at high redshifts) would also result from the large numbers of massive stars.
Earlier, Charlot and Silk (1995) had set upper limits to the WD fraction in galactic halos from the absence of the luminosity signature of the WD progenitors in deep galaxy surveys.
ecf.hq.eso.org /~ralbrech/sepdec97apjl/975392.html   (3624 words)

The brightest objects in the halo are the
The stars that are lost move on in orbits similar to that of the cluster and populate the halo of the Milky Way.
This also seems very plausible, because the galactic orbit of NGC 6712 is such that it frequently dives deeply into the dense regions near the Galactic Center and Bulge.
www.eso.org /outreach/press-rel/pr-1999/pr-04-99.html   (2016 words)

 Extended galactic halo   (Site not responding. Last check: 2007-10-04)
The other possible galactic solution is given by an extended halo around our Galaxy.
On the other hand, if this halo would be largely extended we should observe it in the close-by Andromeda galaxy.
The main concern on this geometrical location is that the existence of the extended halo must be postulated ad-hoc for the GRBs, since no evidence for it is gained for any other class of celestial objects.
www.tesre.bo.cnr.it /~amati/tesi/node90.html   (191 words)

 CERN Courier - Not enough stellar mass obje - IOP Publishing - article
Either the Newtonian/Einsteinian laws of dynamics are wrong at the galactic scale, or there exists some form of galactic matter that does not emit or absorb enough electromagnetic radiation to be directly "visible".
Combined with their previous limits, this enables them to exclude a galactic halo fully comprised of objects of up to four solar masses - quite a respectable mass for a stellar object.
Old white dwarf stars are another possibility: there are counter-arguments to their abundant presence in the halo, but they have the advantage that they could be detected by looking for nearby, dim high-velocity objects.
www.cerncourier.com /main/article/40/4/13   (1804 words)

 RSAA Annual Report 1998
It might then be possible to use these signatures as an alternative way to assess the fraction of the general galactic halo that has come from the disruption of dSph galaxies.
Comparing them with similar data for the oldest stars in Galactic globular clusters (both nearby clusters and one in the extremity of the halo), and with globular clusters in the Large Magellanic Cloud (LMC), produced a very interesting and surprising outcome.
Their dark halos are smaller in size and the particles in them move more slowly.
msowww.anu.edu.au /annualReport/1998/04_shighlights.html   (1264 words)

 The Spherical Component | Guide | Digital Universe | Hayden Planetarium
The bulge is the brightest part of the Galaxy and contains the Galactic bar and nucleus.
The Galactic halo is a large, roughly spherical volume that encompasses the entire Galactic disk.
The stars in the halo and inside globular clusters are metal-poor, older stars that formed close to the era of Galaxy formation.
www.haydenplanetarium.org /universe/duguide/mwt_spherical_comp.php   (331 words)

 SPACE.com -- The New Tourist's Guide to the Milky Way
The galaxy's main disc is surrounded by a halo of old stars and globular clusters (shown in red) in this rendering.
Orphan stars stripped from their parent galaxies and clusters form streamer-like “tidal tails” or else they linger in the galactic halo, where they intermingle with other lone stars.
This galactic bar is believed to be made up of about 30 million stars, stretching 27,000 light-years from end to end.
www.space.com /scienceastronomy/060227_mm_milky_way_tour.html   (1864 words)

 Massive Dark Clusters in the Galactic Halo
For the usual halo model of Cadwell and Ostriker, it may be smaller by only a factor of 2 for distant globular clusters.
is the one-dimensional velocity dispersion of the halo, e is the eccentricity of the GC orbit,
The OC and BSS models are dynamically interesting because the massive dark clusters could contribute significantly to the heating of the stellar disk (Lacey and Ostriker 1985; Carr and Lacey 1987) in contrast to a halo with a hole in the center.
ecf.hq.eso.org /~ralbrech/sepdec97apjl/5353.html   (3142 words)

 The self-enrichment of galactic halo globular cluster: a clue to their formation ?
In the protogalaxy, cold and dense clouds embedded in the hot protogalactic medium are assumed to be the progenitors of galactic halo globular clusters.
The study of the chemical composition and dynamics of the galactic halo components, field metal-poor stars and globular clusters (hereafter GCs), provides a natural way to trace the early phases of the galactic evolution.
Our main conclusion is therefore that galactic halo globular cluster metallicities might be consistent with the process of self-enrichment, both from dynamical and chemical points of view.
vela.astro.ulg.ac.be /themes/stellar/halos/articles/halo2/halo2.html   (7824 words)

 [No title]   (Site not responding. Last check: 2007-10-04)
Originally it was thought that all globular clusters were part of the halo.
The less-metal-poor clusters have a scale height similar to that of the thick disk, and they may be associated.
So there's not a lot of stuff in the stellar halo, but what is there holds a lot of information about the early history of the Galaxy!
burro.astr.cwru.edu /Academics/Astr222/Galaxy/Structure/halo.html   (251 words)

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