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Topic: Galactic bulge

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  Bulge (astronomy) - Wikipedia, the free encyclopedia
The bulge in galaxy spirals is usually composed of Population II stars, small, red and old.
Most bulges are thought to host a supermassive fl hole at their center.
Bulges have similar properties to those of elliptical galaxies (scaled down to lower mass and luminosity).
en.wikipedia.org /wiki/Galactic_bulge   (194 words)

 galactic bulge
The bulge diminishes in size relative to the galactic disk in the sequence of spirals Sa to Sd.
Stars that populate the bulge are normally old, Population II objects, dating back to their galaxy's earliest period.
The original spherical shape lives on in the outermost region of a galaxy, known as the galactic halo, and, to a lesser extent, in the bulge.
www.daviddarling.info /encyclopedia/G/galbulge.html   (266 words)

 Galaxy rotation curve - Wikipedia, the free encyclopedia
Based on this, it would be expected that the average orbital speed of an object at a specified distance away from the majority of the mass distribution would decrease inversely with the square root of the radius of the orbit (the dashed line in Fig.
At the time of the discovery of the discrepancy, it was thought that most of the mass of the galaxy had to be in the galactic bulge, near the center.
This extra mass is proposed by astronomers to be due to dark matter within the galactic halo, the existence of which was first posited by Fritz Zwicky some 40 years earlier in his studies of the masses of galaxy clusters.
en.wikipedia.org /wiki/Galaxy_rotation_problem   (1306 words)

 [No title]   (Site not responding. Last check: 2007-10-26)
Unlike the disk, the distribution of stars in the galactic bulge is not exponential.
It's hard to study the galactic bulge due to dust -- as much as 28 magnitudes of extinction exist within a few degrees of the center.
Bulge stars are mostly old (ages > 9 Gyr) and have a range of metallicities (-1 < [Fe/H] < 0.5) with an average metallicity a little under solar ([Fe/H] = -0.2).
burro.astr.cwru.edu /Academics/Astr222/Galaxy/Structure/bulge.html   (277 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 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.
A galactic region where the evolution of native sapients is suppressed might yet be attractive to settlers arriving from elsewhere.
www.theforce.net /swtc/galaxy.html   (8916 words)

 What is the Galactic Alignment?
The Galactic Alignment is the alignment of the December solstice sun with the Galactic equator.
This Galactic Alignment occurs only once every 26,000 years, and was what the ancient Maya were pointing to with the 2012 end-date of their Long Count calendar.
However, since the nuclear bulge is quite large, this definition is not as precise as saying "the alignment of the December solstice sun with the Galactic equator", which occurs in the range 1980 - 2016.
alignment2012.com /whatisGA.htm   (963 words)

 Galaxy - Wikipedia, the free encyclopedia
When astronomers speculated that certain objects previously classified as spiral nebulae were actually vast congeries of stars, this was called the "island universe theory"; but this was an obvious misnomer, since universe means everything there is. Consequently, this term fell into disuse, replaced by applying the term galaxy generically to all such bodies.
The standard model for such active galactic nucleus is based upon energy generation from matter falling into a supermassive fl hole at the core region.
Within the next billion years, globular clusters, the central supermassive fl hole and galactic bulge of metal-poor Population II stars form.
en.wikipedia.org /wiki/Galaxy   (2686 words)

 [No title]
The dependence of Mv on period for the bulge RR Lyrae stars can be found from the reddening-free magnitude VV-I. The zero point of the Mvlog P relation is set with the horizontal branches of Oosterhoff type I globular clusters.
The best distance modulus to the bulge from the RR Lyrae (ab) stars is 14.45 mag, which compares favorably with the distance modulus of 14.49 mag found from the HADS.
Extrapolation of the existing K band counts to the flux levels expected to be reached by Darwin in 1 hour suggests 5,000 detectable stars (arc sec)^-2 around the compact radio source Sgr A^*, which is commonly believed to be associated with a fl hole of mass 2.6 million M_o.
www.aoc.nrao.edu /~gcnews/gcflash/gcflash_Vol.11_No.6   (896 words)

 Very small galactic bulge could change ideas of galaxy formation
Instead of the old stars that normally populate a galactic bulge, the astronomers found evidence of both young and intermediate-age stars.
While a typical galactic disk is made up of stars of all ages, the bulge normally contains old stars which date from the time the galaxy formed.
The original spherical shape lives on in an outer region of a galaxy known as the "halo" and, to a lesser extent, in the bulge.
www.eurekalert.org /pub_releases/2001-06/OSU-Vsgb-0406101.php   (683 words)

 Spatial Distribution of M31 Novae
By analogy, it is often assumed that Galactic novae also come mainly from the bulge; for example, Della Valle and Duerbeck (1993) and Della Valle and Livio (1994) assume that three-fourths of the Galactic novae are from the bulge.
Because of the presence of true disk novae masquerading as apparent bulge novae, the difference between the B distributions of the apparent disk and apparent bulge novae is smaller than the difference between the B distributions for the true disk and true bulge novae.
Second, while true bulge novae on the top side of the bulge are practically unextinguished, from our vantage point, true bulge novae on the bottom are significantly extinguished by dust that is well out in the disk, where the extinction is largest.
ecf.hq.eso.org /~ralbrech/sepdec97apjl/5210.html   (3104 words)

 Galactic Meeting Abstracts
The Galactic CO survey of Dame, Hartmann, and Thaddeus (2001; hereafter DHT) is composed of both large-scale unbiased surveys, mainly concentrated within 10 deg of the Galactic plane, and targeted observations of clouds at higher latitudes.
Near the Galactic midplane the HII appears to have little relationship to the HI; however, at higher Galactic latitudes the WHAM survey reveals a close relationship, both kinematically and spatially, between the diffuse HII and "warm" (i.e., broad 21 cm component) HI clouds, including the distinct complexes of HI clouds at intermediate and high velocities.
The stellar bulge and halo are more than a context for continuing disk evolution: they provide an opportunity to disentangle the star formation and assembly histories of the older stars in the Galaxy, and to distinguish the distributions of age, chemistry, stars, and mass.
www.bu.edu /iar/galactic_meeting/abstracts.html   (15004 words)

 SPACE.com -- Study of Galaxy's Bulge Reveals It May Not Exist
A strange bulge in a nearby galaxy may not be so strange after all.
New images show that the long-suspected bulge in a galaxy called M33 is, in the best case, smaller than thought, according to astronomers at Ohio State University.
While a typical galactic disk is made up of stars of all ages, a bulge is thought to typically contain old stars dating from the time the galaxy formed.
www.space.com /scienceastronomy/astronomy/galaxy_bulge_010618.html   (513 words)

 Bulge and Nucleus of the Milky Way   (Site not responding. Last check: 2007-10-26)
The bulge of the Milky Way is more spherical than the disk and is composed of stars which are more reddish than those in the disk (===>they are more evolved or low mass, but are still considered Pop I stars).
The central region of the Galactic Bulge (the nucleus) is quite interesting because it shows activity similar to that seen in active galactic nuclei, AGNs (although at a lower level).
The red spiral pattern is Sagitarius A West with Sagittarius A*, the galactic center at the center of the spiral.
zebu.uoregon.edu /~imamura/123/lecture-2/bulge.html   (563 words)

 bayes   (Site not responding. Last check: 2007-10-26)
Observations of Planetary Nebulae in the Galactic Bulge
We find the abundances of O, S, Ar in the Planetary Nebulae in the Galactic Bulge to be comparable with the abundances of the Planetary Nebulae in the Disk, high abundances being maybe slightly more frequent in the Bulge.
The distribution of the N/O ratio does not present in the Galactic Bulge Planetary Nebulae the extension to high values that it presents in the Disk Planetary Nebulae.
astro.u-strasbg.fr /~koppen/papers/fcbulge.html   (157 words)

 [No title]
Key concepts: The Galactic bulge is poorly studied because it is obscured by ~30 mag in the visual.
The bulge stars are generally old, but fairly metal rich, with a wide range of metallicity.
The Galactic nucleus, within the inner molecular ring, is gas rich, with giant molecular clouds, active star formation, massive young stellar clusters, and strong magnetic fields.
www.shef.ac.uk /physics/teaching/phy376/docs/Bulge.doc   (297 words)

 Disk, Bulge and Halo
Given the very considerable radial range of stellar orbits in the Galactic potential, the volume of the Galaxy within 4 kpc of the Sun is sufficiently large to provide a fair sample of the entire stellar population structure of the Milky Way, with two exceptions.
One is the very outer Galactic disk, together with the speculative possibility that there is a significant high angular momentum population in the outer halo.
Since the limiting magnitude is V=20 mag, old turnoff stars at the Galactic bulge and to the disk limits will be observed by GAIA, while any anomalous outer halo population will be discovered, if present, and analysed from the GAIA observations of K-giants, which are complete within the entire Galaxy.
www.rssd.esa.int /SA-general/Projects/GAIA_files/LATEX2HTML/node59.html   (864 words)

 Spaceflight Now | Breaking News | Are massive black holes related to nuclear bulges?
The team was surprised to observe a near-perfect correlation between the orbital speeds of the stars inhabiting the nuclear bulge and the absolute mass of the fl holes at their centres.
The more massive the fl hole, the more swiftly the bulge stars moved, even though the majority of their constituents are much too far away from the fl holes to "feel" their gravity directly.
They reveal that the bulge and the super-massive fl holes at their centres are a single dynamical unit and hence may have formed and evolved in tandem.
spaceflightnow.com /news/n0006/28nuclearbulges   (762 words)

 2 New radial velocities
In the context of a study of expansion velocities of galactic bulge PNe and of PNe with [WC]-type nuclei, accurate radial velocities were measured for a sample of 119 PNe (this sample we will designate ZASW).
From 1983 to 1991, a spectrophotometric survey of galactic PNe was performed at the ESO 1.52 m telescope equipped with the Boller and Chivens spectrograph (see Acker et al.
As the sample included a large number of Galactic bulge PNe, we measured the radial velocities of those 247 PNe despite the low resolution of the spectra.
aanda.u-strasbg.fr:2002 /articles/aas/full/1998/16/ds1391/node2.html   (518 words)

 The Formation of Galactic Bulges - Cambridge University Press
Bulges lie at the center of spiral galaxies.
The Epoch of Bulge Formation: Origin of bulges; Deep sub-mm surveys: High-z ULIRGs and the formation of spheroids; Ages and metallicities for stars in the galactic bulge; Integrated stellar populations of bulges: First results; HST-NICMOS observations of galactic bulges: Ages and dust; Inside-out bulge formation and the origin of the Hubble sequence; Part III.
The Timescales of Bulge Formation: Constraints on the bulge formation timescale from stellar populations; Bulge building with mergers and winds; Role of winds, starbursts, and activity in bulge formation; Dynamical timescales of bulge formation; Part IV.
www.cambridge.org /catalogue/catalogue.asp?isbn=0521663342   (289 words)

 Tidal Disruption
Of the three dominant processes affecting cluster evolution and dispersal, the least well described in most modeling is the effect of Galactic tidal fields, both steady-state and time dependent, especially involving disk and bulge shocking in the time-dependent case.
Not only is the Galactic orbit of any specific cluster at best crudely known, but the present, and especially the past, gravitational field of the inner Galactic disk and bulge are insufficiently known.
Since the clusters with the largest mass-loss rates are those nearest the bulge and disk, identifying such stars from the crowded foreground Galactic populations has proved impossible from present data.
www.rssd.esa.int /SA-general/Projects/GAIA_files/LATEX2HTML/node44.html   (884 words)

Large numbers (N=10000 in the disk, halo and bulge) of eclipsing binaries with periods of 0.25 d to >1000 d would be detected.
Interestingly, the delta Sct stars are good bulge tracers, and would allow an independent measurement of Ro (the distance to the Galactic center), if their period-luminosity relations can be improved (e.g.
There are two requirements that are critical for the variable stars and Galactic structure science: the choice of filters, and the data handling.
vela.astro.ulg.ac.be /themes/telins/lmt/galstr.html   (1034 words)

A different method by Harlow Shapley based on the cataloging of globular clusters lead to a radically different picture: a flat disk with diameter ~70 kiloparsecs and the Sun far from the center.
Life as we know it would seem to be a phenomenon found only around single, third-generation G-type stars in the middle regions of the spiral arms of spiral galaxies, like the sun.
Irregular galaxies have few elderly stars and thus seem to have low concentrations of the heavier elements on which life depends.
www.brainyencyclopedia.com /encyclopedia/g/ga/galaxy.html   (2431 words)

 The nuclear bulge of the Galaxy   (Site not responding. Last check: 2007-10-26)
Models of the Galactic Disk and Bulge are developed in order to correctly decompose the total surface brightness maps of the inner Galaxy and to apply proper extinction corrections.
The Nuclear Bulge appears as a distinct, massive disk-like complex of stars and molecular clouds which is, on a large scale, symmetric with respect to the Galactic Centre.
It is distinguished from the Galactic Bulge by its flat disk-like morphology, very high density of stars and molecular gas, and ongoing star formation.
aanda.u-strasbg.fr:2002 /papers/aa/full/2002/10/aah3107/aah3107.html   (475 words)

 ScienceDaily: Very Small Galactic Bulge Could Change Ideas Of Galaxy Formation
Astronomers Measure Mass Of Smallest Black Hole In A Galactic Nucleus (March 2, 2005) -- A group led by astronomers from Ohio State University and the Technion-Israel Institute of Technology have measured the mass of a unique fl hole, and determined that it is the smallest found so...
Catalog Of Spiral Galaxies Shows Evidence Of Galactic Collisions (April 29, 1999) -- Astronomers compiling a catalog of spiral galaxies have discovered that collisions between such galaxies, as well as near-collisions, are more common than had been...
Equatorial bulge -- An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid.
www.sciencedaily.com /releases/2001/06/010605080041.htm   (1849 words)

 SPACE.com -- The New Tourist's Guide to the Milky Way
These stars as a group tend to be younger than the galactic average, most ranging in age from 1 billion to 10 billion years old.
A galactic traveler nearing the center of the Milky Way will feel a greater pull of gravity as the ship approaches the densest and brightest part of our galaxy, a spherical region known as the central bulge.
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   (1789 words)

 The Outer Regions of the Galactic Bulge: I. Observations.   (Site not responding. Last check: 2007-10-26)
The Outer Regions of the Galactic Bulge: I. Observations.
Stars are selected for spectroscopic follow-up from with a carefully chosen colour-magnitude window, optimized for efficient detection of bulge K giants.
A detailed description of the selection of these stars, the methods used to derive the data, and the reliability of the data, is presented in the paper.
www.cs.wisc.edu /niagara/data/nasa/MNRAS_275_591.xml   (133 words)

 [133.03] HST Proper Motions in the Galactic Bulge
The observed optical depths to microlensing of stars in the Galactic Bulge are difficult to reconcile with our present understanding of Galactic dynamics.
We present a kinematic study of the Bulge stars in 35 fields centered on sources that were previously detected as microlensing events by the MACHO experiment.
Therefore, the mean motion of the lensed sources relative to all stars in the line of sight carries information on kinematics as a function of distance and the importance of streaming motions.
www.aas.org /publications/baas/v37n4/aas207/1166.htm   (286 words)

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