text:
Spiral galaxy
From Wikipedia, the free encyclopedia
Jump to: navigation, search
An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457)
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae[1] and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.
Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.
Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure,[2] extending from the central bulge, at the ends of which the spiral arms begin. The proportion of barred spirals relative to their barless cousins has likely changed over the history of the Universe, with only about 10% containing bars about 8 billion years ago, to roughly a quarter 2.5 billion years ago, until present, where over two-thirds of the galaxies in the visible universe (Hubble volume) have bars.[3]
In the 1970s, our own Milky Way was confirmed to be a barred spiral, although the bar itself is difficult to observe from the Earth's current position within the galactic disc.[4] The most convincing evidence for the stars forming a bar in the galactic center comes from several recent surveys, including the Spitzer Space Telescope .[5]
Together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in today's universe.[6] They are mostly found in low-density regions and are rare in the centers of galaxy clusters.[7]
Contents
[hide]
1 Structure
1.1 Spiral arms
1.2 Galactic bulge
1.3 Galactic spheroid
1.4 Oldest spiral galaxy
2 Origin of the spiral structure
2.1 Density wave model
2.1.1 Historical theory of Lin and Shu
2.1.2 Star formation caused by density waves
2.2 More young stars in spiral arms
2.3 Gravitationally aligned orbits
3 Distribution of stars in spirals
4 Spiral nebula
5 Milky Way
6 Famous examples
7 See also
8 References
9 External links
Structure[edit]
Barred spiral galaxy UGC 12158.
Spiral galaxies consist of five distinct components:
A flat, rotating disc of (mostly newly created) stars and interstellar matter
A central stellar bulge of mainly older stars, which resembles an elliptical galaxy
A near-spherical halo of stars, including many in globular clusters
A supermassive black hole at the very center of the central bulge
A near-spherical dark matter halo
The relative importance, in terms of mass, brightness and size, of the different components varies from galaxy to galaxy.
Spiral arms[edit]
NGC 1300 in infrared light.
Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name. Naturally, different classifications of spiral galaxies have distinct arm-structures. Sc and SBc galaxies, for instance, have very "loose" arms, whereas Sa and SBa galaxies have tightly wrapped arms (with reference to the Hubble sequence). Either way, spiral arms contain many young, blue stars (due to the high mass density and the high rate of star formation), which make the arms so bright.
Galactic bulge[edit]
A bulge is a huge, tightly packed group of stars. The term commonly refers to the central group of stars found in most spiral galaxies.
Using the Hubble classification, the bulge of Sa galaxies is usually composed of Population II stars, that are old, red stars with low metal content. Further, the bulge of Sa and SBa galaxies tends to be large. In contrast, the bulges of Sc and SBc galaxies are much smaller and are composed of young, blue Population I stars. Some bulges have similar properties to those of elliptical galaxies (scaled down to lower mass and luminosity); others simply appear as higher density centers of disks, with properties similar to disk galaxies.
Many bulges are thought to host a supermassive black hole at their centers. Such black holes have never been directly observed, but many indirect proofs exist. In our own galaxy, for instance, the object called Sagittarius A* is believed to be a supermassive black hole. There is a tight correlation between the mass of the black hole and the velocity dispersion of the stars in the bulge, the M-sigma relation.
Galactic spheroid[edit]
Spiral galaxy NGC 1345
The bulk of the stars in a spiral galaxy are located either close to a single plane (the galactic plane) in more or less conventional circular orbits around the center of the galaxy (the Galactic Center), or in a spheroidal galactic bulge around the galactic core.
However, some stars inhabit a spheroidal halo or galactic spheroid, a type of galactic halo. The orbital behaviour of these stars is disputed, but they may describe retrograde and/or highly inclined orbits, or not move in regular orbits at all. Halo stars may be acquired from small galaxies which fall into and merge with the spiral galaxy—for example, the Sagittarius Dwarf Spheroidal 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.
NGC 428 is a barred spiral galaxy, located approximately 48 million light-years away from Earth in the constellation of Cetus.[8]
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 galactic halo also contains many globular clusters.
The motion of halo stars does bring them through the disc on occasion, and a number of small red dwarfs close to the Sun are thought to belong to the galactic halo, for example Kapteyn's Star and Groombridge 1830. Due to their irregular movement around the center of the galaxy—if they do so at all—these stars often display unusually high proper motion.
In 2013 and 2014 papers were published presenting evidence that the spheroid is actually a planar structure in about half of all galaxies.[9]
Oldest spiral galaxy[edit]
The oldest spiral galaxy on file is BX442. At eleven billion years old, it is more than two billion years older than any previous discovery. Researchers think the galaxy’s shape is caused by the gravitational influence of a companion dwarf galaxy. Computer models based on that assumption indicate that BX442's spiral structure will last about 100 million years.[10][11]
Origin of the spiral structure[edit]
Spiral galaxy NGC 6384 taken by Hubble Space Telescope.
A spiral home to exploding stars[12]
The pioneer of studies of the rotation of the Galaxy and the formation of the spiral arms was Bertil Lindblad in 1925. He realized that the idea of stars arranged permanently in a spiral shape was untenable. Since the angular speed of rotation of the galactic disk varies with distance from the centre of the galaxy (via a standard solar system type of gravitational model), a radial arm (like a spoke) would quickly become curved as the galaxy rotates. The arm would, after a few galactic rotations, become increasingly curved and wind around the galaxy ever tighter. This is called the winding problem. Measurements in the late 1960s showed that the orbital velocity of stars in spiral galaxies with respect to their distance from the galactic center is indeed higher than expected from Newtonian dynamics but still cannot explain the stability of the spiral structure.
Since the 1960s, there have been two leading hypotheses or models for the spiral structures of galaxies:
star formation caused by density waves in the galactic disk of the galaxy.
the SSPSF model – star formation caused by shock waves in the interstellar medium.
These different hypotheses do not have to be mutually exclusive, as they may explain different types of spiral arms.
Density wave model[edit]
See also: Density wave theory
Bertil Lindblad proposed that the arms represent regions of enhanced density (density waves) that rotate more slowly than the galaxy’s stars and gas. As gas enters a density wave, it gets squeezed and makes new stars, some of which are short-lived blue stars that light the arms.
Explanation of spiral galaxy arms.
This idea was developed into density wave theory by C. C. Lin and Frank Shu in 1964.[13]
Historical theory of Lin and Shu[edit]
The first acceptable theory for the spiral structure was devised by C. C. Lin and Frank Shu in 1964, attempting to explain the large-scale structure of spirals in terms of a small-amplitude wave propagating with fixed angular velocity, that revolves around the galaxy at a speed different from that of the galaxy's gas and stars. They suggested that the spiral arms were manifestations of spiral density waves - they assumed that the stars travel in slightly elliptical orbits, and that the orientations of their orbits is correlated i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic center. This is illustrated in the diagram. It is clear that the elliptical orbits come close together in certain areas to give the effect of arms. Stars therefore do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.[14]
Star formation caused by density waves[edit]
The following hypotheses exist for star formation caused by density waves:
As gas clouds move into the density wave, the local mass density increases. Since the criteria for cloud collapse (the Jeans instability) depends on density, a higher density makes it more likely for clouds to collapse and form stars.
As the compression wave goes through, it triggers star formation on the leading edge of the spiral arms.
As clouds get swept up by the spiral arms, they collide with one another and drive shock waves through the gas, which in turn causes the gas to collapse and form stars.
The bright galaxy NGC 3810 demonstrates classical spiral structure in this very detailed image from Hubble. Credit: ESA/Hubble and NASA.
More young stars in spiral arms[edit]
The arms appear brighter because there are more young stars (hence more massive, bright stars). These massive, bright stars also die out quickly, which would leave just the darker background stellar distribution behind the waves, hence making the waves visible.
While stars, therefore, do not remain forever in the position that we now see them in, they also do not follow the arms. The arms simply appear to pass through the stars as the stars travel in their orbits.
Gravitationally aligned orbits[edit]
See also: Gravitationally aligned orbits
Charles Francis and Erik Anderson showed from observations of motions of over 20,000 local stars (within 300 parsecs), that stars do move along spiral arms, and described how mutual gravity between stars causes orbits to align on logarithmic spirals. When the theory is applied to gas, collisions between gas clouds generate the molecular clouds in which new stars form, and evolution towards grand-design bisymmetric spirals is explained.[15]
Distribution of stars in spirals[edit]
The similar distribution of stars in Spirals
The stars in spirals are distributed in thin disks with surface luminosity (Freeman, 1970).[16]
I ( r ) = I 0 e − r / R D {\displaystyle I(r)=I_{0}e^{-r/R_{D}}}
with R D {\displaystyle R_{D}} being the disk scale-length; I 0 {\displaystyle I_{0}} is the central value; it is useful to define: R o p t = 3.2 R D {\displaystyle R_{opt}=3.2R_{D}} as the size of the stellar disk, whose luminosity is
L t o t = 2 π I 0 R D 2 {\displaystyle L_{tot}=2\pi I_{0}R_{D}^{2}} .
The spiral's light profiles, in terms of the coordinate r / R D {\displaystyle r/R_{D}} , do not depend on galaxy luminosity.
Spiral nebula[edit]
"Spiral nebula" was a term used to describe galaxies with a visible spiral structure, such as the Whirlpool Galaxy, before it was understood that these objects existed outside our Milky Way galaxy. The question of whether such objects were separate galaxies independent of the Milky Way, or a type of nebula existing within our own galaxy, was the subject of the Great Debate of 1920, between Heber Curtis of Lick Observatory and Harlow Shapley of Mt. Wilson Observatory. Beginning in 1923, Edwin Hubble[17][18] observed Cepheid variables in several spiral nebulae, including the so-called "Andromeda Nebula", proving that they are, in fact, entire galaxies outside our own. The term "spiral nebula" has since fallen into disuse.
Milky Way[edit]
The Milky Way was once considered an ordinary spiral galaxy. Astronomers first began to suspect that the Milky Way is a barred spiral galaxy in the 1990s.[19] Their suspicions were confirmed by Spitzer Space Telescope observations in 2005,[20] which showed that the Milky Way's central bar is larger than was previously suspected.
Milky Way Galaxy Spiral Arms - based on WISE data.
Famous examples[edit]
Andromeda Galaxy
Milky Way
Pinwheel Galaxy
Sunflower Galaxy
Triangulum Galaxy
Whirlpool Galaxy
See also[edit]
Classification
Active galactic nucleus
Disc galaxy
Dwarf galaxy
Dwarf elliptical galaxy
Dwarf spheroidal galaxy
Galaxy color–magnitude diagram
Grand design spiral galaxy
Intermediate spiral galaxy
Lenticular galaxy
Ring galaxy
Starburst galaxy
Seyfert galaxy
Other
Galactic coordinate system
Galactic corona
Galaxy formation and evolution
Groups and clusters of galaxies
List of galaxies
List of nearest galaxies
Tully–Fisher relation
Galaxy rotation curve
Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure
References[edit]
Jump up ^ Hubble, E.P. (1936). The realm of the nebulae (PDF). Mrs. Hepsa Ely Silliman memorial lectures, 25. New Haven: Yale University Press. ISBN 9780300025002. OCLC 611263346. Archived from the original on 2012-09-29. (pp. 124–151)
Jump up ^ D. Mihalas (1968). Galactic Astronomy. W. H. Freeman. ISBN 978-0-7167-0326-6.
Jump up ^ "Hubble and Galaxy Zoo Find Bars and Baby Galaxies Don't Mix". Science Daily. 16 January 2014.
Jump up ^ Ripples in a Galactic Pond, Scientific American, October 2005
Jump up ^ R. A. Benjamin; E. Churchwell; B. L. Babler; R. Indebetouw; M. R. Meade; B. A. Whitney; C. Watson; M. G. Wolfire; M. J. Wolff; R. Ignace; T. M. Bania; S. Bracker; D. P. Clemens; L. Chomiuk; M. Cohen; J. M. Dickey; J. M. Jackson; H. A. Kobulnicky; E. P. Mercer; J. S. Mathis; S. R. Stolovy; B. Uzpen (September 2005). "First GLIMPSE Results on the Stellar Structure of the Galaxy". The Astrophysical Journal Letters. 630 (2): L149–L152. arXiv:astro-ph/0508325  . Bibcode:2005ApJ...630L.149B. doi:10.1086/491785.
Jump up ^ Loveday, J. (February 1996). "The APM Bright Galaxy Catalogue". Monthly Notices of the Royal Astronomical Society. 278 (4): 1025–1048. arXiv:astro-ph/9603040  . Bibcode:1996MNRAS.278.1025L. doi:10.1093/mnras/278.4.1025.
Jump up ^ Dressler, A. (March 1980). "Galaxy morphology in rich clusters — Implications for the formation and evolution of galaxies". The Astrophysical Journal. 236: 351–365. Bibcode:1980ApJ...236..351D. doi:10.1086/157753.
Jump up ^ "A mess of stars". Retrieved 11 August 2015.
Jump up ^ "Recent work has shown that the Milky Way and the Andromeda galaxies both possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures." http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13481.html "The origin of planar dwarf galaxy structures remains unexplained in the standard paradigm of galaxy formation." http://arxiv.org/abs/1406.1799 "This is a big problem that contradicts our standard cosmological models. It challenges our understanding of how the universe works including the nature of dark matter." Geraint F. Lewis quoted in http://phys.org/news/2014-07-mysterious-dwarfs-cosmic-rethink.html "There's a very serious conflict, and the repercussion is we do not seem to have the correct theory of gravity" Pavel Kroupa as quoted in http://phys.org/news/2014-06-universe-dwarf-galaxies-dont-standard.html
Jump up ^ Oldest spiral galaxy is a freak of cosmos http://www.zmescience.com/space/oldest-spiral-galaxy-31321/
Jump up ^ Gonzalez, Robert T. (19 July 2012). "Hubble Has Spotted an Ancient Galaxy That Shouldn't Exist". io9. Retrieved 10 September 2012.
Jump up ^ "A spiral home to exploding stars". ESA / Hubble. Retrieved 2 April 2014.
Jump up ^ Lin, C. C.; Shu, F. H. (August 1964). "On the spiral structure of disk galaxies". The Astrophysical Journal. 140: 646–655. Bibcode:1964ApJ...140..646L. doi:10.1086/147955.
Jump up ^ Henbest, Nigel (1994), The Guide to the Galaxy, Cambridge University Press, p. 74, ISBN 9780521458825, Lin and Shu showed that this spiral pattern would persist more or less for ever, even though individual stars and gas clouds are always drifting into the arms and out again .
Jump up ^ Francis, C.; Anderson, E. (2009). "Galactic spiral structure". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 465 (2111): 3425. arXiv:0901.3503  . Bibcode:2009RSPSA.465.3425F. doi:10.1098/rspa.2009.0036.
Jump up ^ Freeman, K. C. (1970). "On the Disks of Spiral and so Galaxies". Astrophysical Journal. 160: 811. Bibcode:1970ApJ...160..811F. doi:10.1086/150474.
Jump up ^ "NASA - Hubble Views the Star That Changed the Universe".
Jump up ^ Hubble, E. P. (May 1926). "A spiral nebula as a stellar system: Messier 33". The Astrophysical Journal. 63: 236–274. Bibcode:1926ApJ....63..236H. doi:10.1086/142976.
Jump up ^ Chen, W.; Gehrels, N.; Diehl, R.; Hartmann, D. (1996). "On the spiral arm interpretation of COMPTEL 26Al map features". Space Science Reviews. 120: 315–316. Bibcode:1996A&AS..120C.315C.
Jump up ^ McKee, Maggie (August 16, 2005). "Bar at Milky Way's heart revealed". New Scientist. Retrieved 17 June 2009.
External links[edit]
Wikimedia Commons has media related to Spiral galaxies.
Giudice, G.F.; Mollerach, S.; Roulet, E. (1994). "Can EROS/MACHO be detecting the galactic spheroid instead of the galactic halo?". Physical Review D. 50 (4): 2406–2413. arXiv:astro-ph/9312047  . Bibcode:1994PhRvD..50.2406G. doi:10.1103/PhysRevD.50.2406.
Stephens, Tim (6 March 2007). "AEGIS survey reveals new principle governing galaxy formation and evolution". UC Santa Cruz. Archived from the original on 11 March 2007. Retrieved 24 May 2006.
Spiral Galaxies @ SEDS Messier pages
SpiralZoom.com, an educational website about Spiral Galaxies and other spiral formations found in nature. For high school & general audience.
Spiral Structure explained
GLIMPSE: the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire
Merrifield, M. R. "Spiral Galaxies and Pattern Speed". Sixty Symbols. Brady Haran for the University of Nottingham.
[show]
v
t
e
Galaxies
Morphology
Disc galaxy
Lenticular galaxy
barred
unbarred
Spiral galaxy
Anemic galaxy
barred
flocculent
grand design
intermediate
Magellanic
unbarred
Dwarf galaxy
elliptical
irregular
spheroidal
spiral
Elliptical galaxy
cD-galaxy
Irregular galaxy
barred
Peculiar galaxy
Ring galaxy
Polar
Structure
Active galactic nucleus (AGN)
Bar
Bulge
Dark matter halo
Disc
Galactic halo
corona
Galactic plane
Interstellar medium
Protogalaxy
Spiral arm
Supermassive black hole
Active nuclei
Blazar
LINER
Markarian galaxies
Quasar
Radio galaxy
X-shaped
Relativistic jet
Seyfert galaxy
Energetic galaxies
LAE
LIRG
Starburst galaxy
BCD
Pea
Hot, dust-obscured galaxies (Hot DOGs)
Low activity
LSB
UDG
Interaction
Field galaxy
Galactic tide
Galaxy cloud
Galaxy groups and clusters
Galaxy group
Galaxy cluster
Brightest cluster galaxy
Fossil galaxy group
Interacting galaxy
merger
Jellyfish galaxy
Satellite galaxy
Stellar stream
Superclusters
Walls
Void galaxy
Voids and supervoids
Lists
Galaxies
Galaxies named after people
Largest
Nearest
Polar-ring galaxies
Ring galaxies
Spiral galaxies
Groups and clusters
Large quasar groups
Quasars
Superclusters
Voids
See also
Dark galaxy
Extragalactic astronomy
Faint blue galaxy
Galactic astronomy
Galactic center
Galactic coordinate system
Galactic empire
Galactic habitable zone
Galactic magnetic fields
Galactic orientation
Galactic quadrant
Galactic ridge
Galaxy color–magnitude diagram
Galaxy formation and evolution
Galaxy rotation curve
Illustris project
Intergalactic dust
Intergalactic stars
Intergalactic travel
Population III stars
Cosmos Redshift 7 galaxy
Book
Category
Portal
[show]
v
t
e
The Milky Way
Location
Milky Way → Milky Way subgroup → Local Group → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe
Each arrow (→) may be read as "within" or "part of".
Galactic core
Center of the Milky Way
Sagittarius A
Sagittarius A*
Supermassive black hole
Spiral arms
Carina–Sagittarius
Norma–Cygnus
Orion–Cygnus
Perseus
Scutum–Centaurus
Satellite galaxies
Magellanic Clouds
Large Magellanic Cloud
Small Magellanic Cloud
Magellanic Stream
Magellanic Bridge
Sagittarius Spheroidal
Sagittarius Stream
Boötes II
Coma Berenices
Messier 54
Palomar 12
Segue 1
Segue 2
Terzan 7
Dwarfs
Boötes I
Boötes III
Canes Venatici I
Canes Venatici II
Canis Major
Carina
Crater 2
Draco
Fornax
Hercules
Leo I
Leo II
Leo IV
Leo V
Leo T
Phoenix
Pisces I
Pisces II
Sculptor
Sextans
Triangulum II
Ursa Major I
Ursa Major II
Ursa Minor
Virgo I
Other
Monoceros Ring
Virgo Stream
Koposov I
Koposov II
Segue 3
Willman 1
Related
Andromeda–Milky Way collision
Astronomy portal
Authority control
GND: 4182349-7
Retrieved from "https://en.wikipedia.org/w/index.php?title=Spiral_galaxy&oldid=821648737"
Categories:
Spiral galaxies
Galaxy morphological types
Spirals
Hidden categories:
Use dmy dates from January 2014
Wikipedia articles with GND identifiers
Navigation menu
Personal tools
Not logged in
Talk
Contributions
Create account
Log in
Namespaces
Article
Talk
Variants
Views
Read
Edit
View history
More
Search
Navigation
Main page
Contents
Featured content
Current events
Random article
Donate to Wikipedia
Wikipedia store
Interaction
Help
About Wikipedia
Community portal
Recent changes
Contact page
Tools
What links here
Related changes
Upload file
Special pages
Permanent link
Page information
Wikidata item
Cite this page
Print/export
Create a book
Download as PDF
Printable version
In other projects
Wikimedia Commons
Wikiversity
Languages
Afrikaans
العربية
বাংলা
Bân-lâm-gú
Беларуская
Български
Bosanski
Català
Čeština
Corsu
Deutsch
Eesti
Ελληνικά
Español
Esperanto
Euskara
فارسی
Français
Gaeilge
Galego
한국어
हिन्दी
Hrvatski
Bahasa Indonesia
Italiano
עברית
Lëtzebuergesch
Lietuvių
Magyar
Македонски
मराठी
مازِرونی
Монгол
မြန်မာဘာသာ
Nederlands
नेपाली
日本語
Norsk
Norsk nynorsk
Occitan
ਪੰਜਾਬੀ
پنجابی
Polski
Português
Română
Русский
Scots
Simple English
Slovenčina
Српски / srpski
Srpskohrvatski / српскохрватски
Suomi
Svenska
ไทย
Türkçe
Українська
Tiếng Việt
中文
Edit links
This page was last edited on 21 January 2018, at 19:58.
Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
Privacy policy
About Wikipedia
Disclaimers
Contact Wikipedia
Developers
Cookie statement
Mobile view
Enable previews

values: mw-page-base noprint

values: mw-head-base noprint

values: firstHeading firstHeading en

values: siteSub noprint

values: jump-to-nav mw-jump

attrs: alt src width height class srcset data-file-width data-file-height

attrs: href class title

attrs: class style

value: b

value: sup

values:
/wiki/Population_II_star
mw-redirect
Population II star

values:
/wiki/Population_I_star
mw-redirect
Population I star

values:
/wiki/M-sigma_relation
mw-redirect
M-sigma relation

values:
/wiki/Retrograde_motion
mw-redirect
Retrograde motion

values:
/wiki/Cetus_(constellation)
mw-redirect
Cetus (constellation)

values:
/wiki/Interstellar_dust
mw-redirect
Interstellar dust

values:
/wiki/Population_II
mw-redirect
Population II

values:
/wiki/Population_I
mw-redirect
Population I

values: Edit section: Origin of the spiral structure

values:
/wiki/Rotation_curve
mw-redirect
Rotation curve

values:
/wiki/Galactic_disk
mw-redirect
Galactic disk

values: Edit section: Historical theory of Lin and Shu

values: Edit section: Star formation caused by density waves

values:
/wiki/Shock_waves
mw-redirect
Shock waves

values: Edit section: More young stars in spiral arms

values: Edit section: Gravitationally aligned orbits

values:
/wiki/Molecular_clouds
mw-redirect
Molecular clouds

values: Edit section: Distribution of stars in spirals

values: vertical-align: -0.838ex; width:15.88ex; height:3.343ex;

values: vertical-align: -0.671ex; width:3.357ex; height:2.509ex;

values: vertical-align: -0.671ex; width:2.077ex; height:2.509ex;

values: vertical-align: -1.005ex; width:13.641ex; height:2.843ex;

values: vertical-align: -1.005ex; width:14.827ex; height:3.176ex;

values: vertical-align: -0.838ex; width:5.568ex; height:2.843ex;

values:
/wiki/Heber_Curtis
mw-redirect
Heber Curtis

values:
/wiki/Mt._Wilson_Observatory
mw-redirect
Mt. Wilson Observatory

values:
/wiki/Cepheid_variables
mw-redirect
Cepheid variables

values: -moz-column-width: 20em; -webkit-column-width: 20em; column-width: 20em;

values:
nofollow
external text
//www.worldcat.org/oclc/611263346

values:
/wiki/Astrophysical_Journal
mw-redirect
Astrophysical Journal

values:
nofollow
external text
//arxiv.org/abs/astro-ph/0508325

values:
nofollow
external text
//doi.org/10.1086%2F491785

values:
nofollow
external text
//arxiv.org/abs/astro-ph/9603040

values:
nofollow
external text
//doi.org/10.1093%2Fmnras%2F278.4.1025

values:
nofollow
external text
//doi.org/10.1086%2F157753

values:
nofollow
external free
http://arxiv.org/abs/1406.1799

values:
nofollow
external text
//doi.org/10.1086%2F147955

values:
nofollow
external text
//arxiv.org/abs/0901.3503

values:
nofollow
external text
//doi.org/10.1098%2Frspa.2009.0036

values:
nofollow
external text
//doi.org/10.1086%2F150474

values:
nofollow
external text
//doi.org/10.1086%2F142976

values: -moz-column-width: 35em; -webkit-column-width: 35em; column-width: 35em; list-style-type: decimal;

values:
nofollow
external text
//arxiv.org/abs/astro-ph/9312047

values:
nofollow
external text
//doi.org/10.1103%2FPhysRevD.50.2406

values:
nofollow
external text
http://messier.seds.org/spir.html

values:
nofollow
http://www.astro.wisc.edu/sirtf/
external text

values:
row
navbox-group
text-align: center;;width:1%

values:
/wiki/Spiral_arm#Spiral_arms
mw-redirect
Spiral arm

values: Low-ionization nuclear emission-line region

values:
/wiki/Polar_jet#Relativistic_jet
mw-redirect
Polar jet

values:
/wiki/Galaxy_cloud
mw-redirect
Galaxy cloud

values:
/wiki/Fossil_galaxy_group
mw-redirect
Fossil galaxy group

values:
/wiki/Galactic_center
mw-redirect
Galactic center

values:
/wiki/Galactic_magnetic_fields
mw-redirect
Galactic magnetic fields

values: nowraplinks hlist collapsible autocollapse navbox-inner

values:
navbox-image
5
width:1px;padding:0px 0px 0px 2px

values: List of satellite galaxies of the Milky Way

values: nowraplinks collapsible autocollapse navbox-inner

values:
nofollow
external text
https://d-nb.info/gnd/4182349-7

values: Category:Use dmy dates from January 2014

values: Category:Wikipedia articles with GND identifiers

values: Discussion about edits from this IP address [ctrl-alt-n]

values: A list of edits made from this IP address [ctrl-alt-y]

values: You are encouraged to create an account and log in; however, it is not mandatory

values: You're encouraged to log in; however, it's not mandatory. [ctrl-alt-o]

values:
/wiki/Spiral_galaxy
View the content page [ctrl-alt-c]
c

values: Discussion about the content page [ctrl-alt-t]

values: p-namespaces navigation vectorTabs p-namespaces-label

values:
p-variants
navigation
vectorMenu emptyPortlet
p-variants-label

values: Past revisions of this page [ctrl-alt-h]

values: p-views navigation vectorTabs p-views-label

values:
p-cactions
navigation
vectorMenu emptyPortlet
p-cactions-label

values:
mw-wiki-logo
/wiki/Main_Page
Visit the main page

values:
/wiki/Main_Page
Visit the main page [ctrl-alt-z]
z

values: Featured content – the best of Wikipedia

values: Find background information on current events

values:
/wiki/Special:Random
Load a random article [ctrl-alt-x]
x

values: portal navigation p-navigation p-navigation-label

values: Guidance on how to use and edit Wikipedia

values: About the project, what you can do, where to find things

values:
uls-settings-trigger
Language settings
0
button
true

values: مجرة حلزونية – Arabic

values: সর্পিল ছায়াপথ – Bangla

values: Спіральная галактыка – Belarusian

values: Спирална галактика – Bulgarian

values: Σπειροειδής γαλαξίας – Greek

values: کهکشان مارپیچی – Persian

values: सर्पिल गैलेक्सी – Hindi

values: גלקסיה ספירלית – Hebrew

values: Спирална галаксија – Macedonian

values: सर्पिलाकार दीर्घिका – Marathi

values: مرپیچی کهکشون – Mazanderani

values: Мушгиа галактик – Mongolian

values: ခရုပတ်ပုံစံ ဂလက်ဆီ – Burmese

values: सर्पिल गैलेक्सी – Nepali

values: ਸਰਪਿਲ ਆਕਾਸ਼ਗੰਗਾ – Punjabi

values: چکری تارہ سمندر – Western Punjabi

values: Спиральная галактика – Russian

values: Спирална галаксија – Serbian

values: ดาราจักรชนิดก้นหอย – Thai

values: Спіральні галактики – Ukrainian

values: mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject page-Spiral_galaxy rootpage-Spiral_galaxy skin-vector action-view