• Observations using larger telescopes of a few nearby bright galaxies, like the Andromeda Galaxy, began resolving them into huge conglomerations of stars, but based simply
    on the apparent faintness and sheer population of stars, the true distances of these objects placed them well beyond the Milky Way.

  • These structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy—that as the two galaxy centers approach, they start to oscillate around a center
    point, and the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water.

  • Since the Hubble sequence is entirely based upon visual morphological type (shape), it may miss certain important characteristics of galaxies such as star formation rate in
    starburst galaxies and activity in the cores of active galaxies.

  • Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of
    dark matter which extends beyond the visible component, as demonstrated by the universal rotation curve concept.

  • [81] Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered.

  • Wilson telescope, Edwin Hubble was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing
    him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.

  • [28][29] In 1750, English astronomer Thomas Wright, in his An Original Theory or New Hypothesis of the Universe, correctly speculated that it might be a rotating body of a
    huge number of stars held together by gravitational forces, akin to the Solar System but on a much larger scale, and that the resulting disk of stars could be seen as a band on the sky from our perspective inside it.

  • They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.

  • [84][85] Starburst Main article: Starburst galaxy M82, a starburst galaxy that has ten times the star formation of a “normal” galaxy[86] Stars are created within galaxies
    from a reserve of cold gas that forms giant molecular clouds.

  • Particularly, surveys in the Zone of Avoidance (the region of sky blocked at visible-light wavelengths by the Milky Way) have revealed a number of new galaxies.

  • [55] The Hubble Deep Field, an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion (1.25×1011) galaxies in the
    observable universe.

  • [77] Such an event may have affected the Andromeda Galaxy, as it displays a multi-ring-like structure when viewed in infrared radiation.

  • Extremely luminous, they were first identified as high redshift sources of electromagnetic energy, including radio waves and visible light, that appeared more similar to stars
    than to extended sources similar to galaxies.

  • To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well
    as the significant Doppler shift.

  • About one-tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies.

  • [96] They are strong enough to be dynamically important, as they: • Drive mass inflow into the centers of galaxies • Modify the formation of spiral arms • Can affect the rotation
    of gas in the galaxies’ outer regions • Provide the transport of angular momentum required for the collapse of gas clouds, and hence the formation of new stars The typical average equipartition strength for spiral galaxies is about 10 μG (microgauss)
    or 1 nT (nanotesla).

  • [31] Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane; but after Robert Julius Trumpler quantified this
    effect in 1930 by studying open clusters, the present picture of our host galaxy emerged.

  • Seen in visible light, most look like normal spiral galaxies; but when studied under other wavelengths, their cores’ luminosity is equivalent to the luminosity of whole galaxies
    the size of the Milky Way.

  • [49] Modern research Rotation curve of a typical spiral galaxy: predicted based on the visible matter (A) and observed (B).

  • Radio-faint galaxies like M 31 and M33, our Milky Way’s neighbors, have weaker fields (about 5 μG), while gas-rich galaxies with high star-formation rates, like M 51, M 83
    and NGC 6946, have 15 μG on average.

  • This suggests that galaxies are largely formed by dark matter, and that the minimum size may indicate a form of warm dark matter incapable of gravitational coalescence on
    a smaller scale.

  • Instead, they are dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions.

  • “[25] Andalusian astronomer Ibn Bâjjah (“Avempace”, d. 1138) proposed that it was composed of many stars that almost touched one another, and appeared to be a continuous image
    due to the effect of refraction from sublunary material,[21][26] citing his observation of the conjunction of Jupiter and Mars as evidence of this occurring when two objects were near.

  • Many elliptical galaxies are believed to form due to the interaction of galaxies, resulting in a collision and merger.

  • [32] The first project to describe the shape of the Milky Way and the position of the Sun was undertaken by William Herschel in 1785 by counting the number of stars in different
    regions of the sky.

  • [68] Hoag’s Object, an example of a ring galaxy Barred spiral galaxy A majority of spiral galaxies, including our own Milky Way galaxy, have a linear, bar-shaped band of stars
    that extends outward to either side of the core, then merges into the spiral arm structure.

  • It may be the same size as the Milky Way, but have a visible star count only one percent of the Milky Way’s.

  • There are multiple classification and naming schemes for AGNs, but those in the lower ranges of luminosity are called Seyfert galaxies, while those with luminosities much
    greater than that of the host galaxy are known as quasi-stellar objects or quasars.

  • They are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, with only a few billion stars.

  • If one of the galaxies is much more massive than the other, the result is known as cannibalism, where the more massive larger galaxy remains relatively undisturbed, and the
    smaller one is torn apart.

  • [40] In 1750, Thomas Wright correctly speculated that the Milky Way was a flattened disk of stars, and that some of the nebulae visible in the night sky might be separate
    Milky Ways.

  • Starburst galaxies were more common during the universe’s early history,[87] but still contribute an estimated 15% to total star production.

  • [20] Aristotle (384–322 BCE), however, believed the Milky Way was caused by “the ignition of the fiery exhalation of some stars that were large, numerous and close together”
    and that the “ignition takes place in the upper part of the atmosphere, in the region of the World that is continuous with the heavenly motions.

  • A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million solar masses, regardless of whether it has thousands or millions
    of stars.

  • The stars of interacting galaxies usually do not collide, but the gas and dust within the two forms interacts, sometimes triggering star formation.

  • In 2021, data from NASA’s New Horizons space probe was used to revise the previous estimate to roughly 200 billion galaxies (2×1011),[7] which followed a 2016 estimate that
    there were two trillion (2×1012) or more[8][9] galaxies in the observable universe, overall, and as many as an estimated 1×1024 stars[10][11] (more stars than all the grains of sand on all beaches of the planet Earth).

  • Consequently, these galaxies also have a low portion of open clusters and a reduced rate of new star formation.

  • Among other things, its data helped establish that the missing dark matter in our galaxy could not consist solely of inherently faint and small stars.

  • He produced a diagram of the shape of the galaxy with the Solar System close to the center.

  • Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer Galileo Galilei used a telescope to study it and discovered it was composed
    of a huge number of faint stars.

  • All the well-known galaxies appear in one or more of these catalogs but each time under a different number.

  • o A ring galaxy has a ring-like structure of stars and interstellar medium surrounding a bare core.

  • [36] In 1734, philosopher Emanuel Swedenborg in his Principia speculated that there might be galaxies outside our own that were formed into galactic clusters that were minuscule
    parts of the universe that extended far beyond what we could see.

  • Today, the galaxy rotation problem is thought to be explained by the presence of large quantities of unseen dark matter.

  • [88] Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly formed stars, including massive stars that ionize the surrounding clouds
    to create H II regions.

  • Milky Way Main article: Milky Way Greek philosopher Democritus (450–370 BCE) proposed that the bright band on the night sky known as the Milky Way might consist of distant

  • The standard model for an active galactic nucleus is based on an accretion disc that forms around a supermassive black hole (SMBH) at the galaxy’s core region.

  • The radiation from an active galactic nucleus results from the gravitational energy of matter as it falls toward the black hole from the disc.

  • [64] A galaxy with poorly defined arms is sometimes referred to as a flocculent spiral galaxy; in contrast to the grand design spiral galaxy that has prominent and well-defined
    spiral arms.

  • A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs
    and the Sun far from the center.

  • Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a tidal interaction with another galaxy.

  • Most 18th- to 19th-century astronomers considered them as either unresolved star clusters or anagalactic nebulae, and were just thought of as a part of the Milky Way, but
    their true composition and natures remained a mystery.

  • “[39] In 1745, Pierre Louis Maupertuis conjectured that some nebula-like objects were collections of stars with unique properties, including a glow exceeding the light its
    stars produced on their own, and repeated Johannes Hevelius’s view that the bright spots were massive and flattened due to their rotation.

  • The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars.

  • Ultra-luminous infrared galaxies (ULIRGs) are at least ten times more luminous still and form stars at rates >180 M☉ yr−1.

  • They are thought to have an increased star formation rate around 30 times faster than the Milky Way.

  • Observation history The realization that we live in a galaxy that is one among many parallels major discoveries about the Milky Way and other nebulae.

  • [17][18] In the astronomical literature, the capitalized word “Galaxy” is often used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our

  • A significant portion of the galaxy’s total energy output is emitted by the active nucleus instead of its stars, dust and interstellar medium.

  • Some galaxies have been observed to form stars at an exceptional rate, which is known as a starburst.

  • “[27] The shape of the Milky Way as estimated from star counts by William Herschel in 1785; the Solar System was assumed to be near the center.

  • A ring galaxy is thought to occur when a smaller galaxy passes through the core of a spiral galaxy.

  • The Milky Way’s central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun.

  • Galaxies range in size from dwarfs with just a few hundred million (108) stars to giants with one hundred trillion (1014) stars,[3] each orbiting its galaxy’s center of mass.

  • [92] Blazars Main article: Blazar Blazars are believed to be active galaxies with a relativistic jet pointed in the direction of Earth.

  • In the 1970s, Vera Rubin uncovered a discrepancy between observed galactic rotation speed and that predicted by the visible mass of stars and gas.

  • [8][9] However, later observations with the New Horizons space probe from outside the zodiacal light reduced this to roughly 200 billion (2×1011).

  • [70] Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.

  • The prototype example of such a starburst-forming interaction is M82, which experienced a close encounter with the larger M81.

  • They are very large with an upward diameter of 437,000 light-years (compared to the Milky Way’s 100,000 light-year diameter).

  • Formation Artist’s impression of a protocluster forming in the early universe[97] Current models of the formation of galaxies in the early universe are based on the ΛCDM model.


Works Cited

[‘Galaxies to the left side of the Hubble classification scheme are sometimes referred to as “early-type”, while those to the right are “late-type”.
2. ^ The term “field galaxy” is sometimes used to mean an isolated galaxy, although the same term is
also used to describe galaxies that do not belong to a cluster but may be a member of a group of galaxies.
3. Sparke & Gallagher 2000, p. i
4. ^ Hupp, E.; Roy, S.; Watzke, M. (August 12, 2006). “NASA Finds Direct Proof of Dark Matter”. NASA.
Archived from the original on March 28, 2020. Retrieved April 17, 2007.
5. ^ Uson, J. M.; Boughn, S. P.; Kuhn, J. R. (1990). “The central galaxy in Abell 2029 – An old supergiant”. Science. 250 (4980): 539–540. Bibcode:1990Sci…250..539U. doi:10.1126/science.250.4980.539.
PMID 17751483. S2CID 23362384.
6. ^ Hoover, A. (June 16, 2003). “UF Astronomers: Universe Slightly Simpler Than Expected”. Hubble News Desk. Archived from the original on July 20, 2011. Retrieved March 4, 2011.
1. Based upon: Graham, A. W.; Guzman,
R. (2003). “HST Photometry of Dwarf Elliptical Galaxies in Coma, and an Explanation for the Alleged Structural Dichotomy between Dwarf and Bright Elliptical Galaxies”. The Astronomical Journal. 125 (6): 2936–2950. arXiv:astro-ph/0303391. Bibcode:2003AJ….125.2936G.
doi:10.1086/374992. S2CID 13284968.
7. ^ Jump up to:a b Jarrett, T. H. “Near-Infrared Galaxy Morphology Atlas”. California Institute of Technology. Archived from the original on August 2, 2012. Retrieved January 9, 2007.
8. ^ Finley, D.; Aguilar,
D. (November 2, 2005). “Astronomers Get Closest Look Yet At Milky Way’s Mysterious Core”. National Radio Astronomy Observatory. Archived from the original on December 20, 2015. Retrieved August 10, 2006.
9. ^ “Astronomers were wrong about the number
of galaxies in universe”. The Jerusalem Post | Archived from the original on January 14, 2021. Retrieved January 14, 2021.
10. ^ Jump up to:a b Christopher J. Conselice; et al. (2016). “The Evolution of Galaxy Number Density at z
< 8 and its Implications “. The Astrophysical Journal. 830 (2): 83. arXiv:1607.03909. Bibcode:2016ApJ…830…83C. doi:10.3847/0004-637X/830/2/83. S2CID 17424588.
11. ^ Jump up to:a b Fountain, Henry (October 17, 2016). “Two Trillion Galaxies, at the
Very Least “. The New York Times. Archived from the original on December 31, 2019. Retrieved October 17, 2016.
12. ^ Staff (2019). “How Many Stars Are There In The Universe?
“. European Space Agency. Archived from the original on September 23, 2019. Retrieved September 21, 2019.
13. ^ Marov, Mikhail Ya. (2015). “The Structure of the Universe “. The Fundamentals of Modern Astrophysics. pp. 279–294. doi:10.1007/978-1-4614-8730-2_10. ISBN 978-1-4614-8729-6.
14. ^ Mackie, Glen (February 1, 2002). “To see the Universe in a Grain of Taranaki Sand
“. Centre for Astrophysics and Supercomputing. Archived from the original on December 23, 2018. Retrieved January 28, 2017.
15. ^ “Galaxy Clusters and Large-Scale Structure “. University of Cambridge. Archived from the original on May 24, 2012. Retrieved January 15, 2007.
16. ^ Gibney, Elizabeth (2014). “Earth\ ‘s new address: ‘Solar System, Milky Way, Laniakea ‘”. Nature. doi:10.1038/nature.2014.15819. S2CID 124323774.
17. ^ C. T. Onions et al., The Oxford Dictionary of English Etymology, Oxford, 1966, p. 385.
18. ^ Jump up to:a b Harper, D. “galaxy”. Online Etymology Dictionary. Archived from the original on May 27, 2012. Retrieved November 11, 2011.
19. ^ Waller & Hodge 2003, p. 91
20. ^ Konečný, Lubomír. “Emblematics, Agriculture, and Mythography in The Origin of the Milky Way” (PDF). Academy of Sciences of the Czech Republic. Archived from the original (PDF) on July 20, 2006. Retrieved January 5, 2007.
21. ^ Rao, J. (September 2, 2005). “Explore the Archer’s Realm
“. Archived from the original on October 31, 2010. Retrieved January 3, 2007.
22. ^ Plutarch (2006). The Complete Works Volume 3: Essays and Miscellanies. Echo Library. p. 66. ISBN 978-1-4068-3224-2. Archived from the original on March 24, 2021. Retrieved July 25, 2018.
23. ^ Jump up to:a b c Montada, J. P. (September 28, 2007). “Ibn Bâjja
“. Stanford Encyclopedia of Philosophy. Archived from the original on March 16, 2020. Retrieved July 11, 2008.
24. ^ Heidarzadeh 2008, pp. 23–25
25. ^ Mohamed 2000, pp. 49–50
26. ^ Bouali, H.-E.; Zghal, M.; Lakhdar, Z. B. (2005). “Popularisation of Optical Phenomena: Establishing the First Ibn Al-Haytham Workshop on Photography
” (PDF). The Education and Training in Optics and Photonics Conference. Archived (PDF) from the original on May 24, 2011. Retrieved July 8, 2008.
27. ^ O’Connor, John J.; Robertson, Edmund F., “Abu Arrayhan Muhammad ibn Ahmad al-Biruni “, MacTutor History of Mathematics archive, University of St Andrews
28. ^ Heidarzadeh 2008, p. 25, Table 2.1
29. ^ Livingston, J. W. (1971). “Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against
Astrological Divination and Alchemical Transmutation
“. Journal of the American Oriental Society. 91 (1): 96–103 [99]. doi:10.2307/600445. JSTOR 600445.
30. ^ Galileo Galilei, Sidereus Nuncius (Venice, (Italy): Thomas Baglioni, 1610), pages 15 and 16.
English translation: Galileo Galilei with Edward Stafford Carlos, trans., The Sidereal Messenger (London, England: Rivingtons, 1880), pages 42 and 43.
31. ^ O’Connor, J. J.; Robertson, E. F. (November 2002). “Galileo Galilei
“. University of St. Andrews. Archived from the original on May 30, 2012. Retrieved January 8, 2007.
32. ^ Thomas Wright, An Original Theory or New Hypothesis of the Universe … (London, England: H. Chapelle, 1750). From p.48: Archived November 20, 2016, at the Wayback Machine “… the stars are not infinitely dispersed and distributed in a promiscuous manner throughout all the mundane space, without order or design, … this phænomenon [is] no other than a certain effect arising from the observer ‘s situation, … To a spectator placed in an indefinite space, … it [i.e., the Milky Way (Via Lactea)] [is] a vast ring of stars …”
On page 73 Archived November 20, 2016, at the Wayback Machine, Wright called the Milky Way the Vortex Magnus (the great whirlpool) and estimated its diameter at 8.64×1012 miles (13.9×1012 km).
33. ^ Jump up to:a b c d Evans, J. C. (November 24, 1998). “Our Galaxy”. George Mason University. Archived from the original on June 30, 2012. Retrieved January 4, 2007.
34. ^ Immanuel Kant, [ Archived November 20, 2016, at the Wayback Machine Allgemeine Naturgeschichte und Theorie des Himmels …] [Universal Natural History and Theory of the Heavens …], (Königsberg and Leipzig, (Germany): Johann Friederich Petersen, 1755).
Available in English translation by Ian Johnston at: Vancouver Island University, British Columbia, Canada Archived August 29, 2014, at the Wayback Machine
35. ^ William Herschel (1785). “XII. On the construction of the heavens”. Giving Some Accounts of the Present Undertakings, Studies, and Labours, of the Ingenious, in Many Considerable Parts of the World. Philosophical Transactions of the Royal Society of London. Vol. 75. London. pp. 213–266. doi:10.1098/rstl.1785.0012. ISSN 0261-0523. S2CID 186213203. Archived from the original on November 20, 2016. Retrieved January 27, 2016. Herschel’s diagram of the galaxy appears immediately after the article ‘s last page.
36. ^ Paul 1993, pp. 16–18
37. ^ Trimble, V. (1999). “Robert Trumpler and the (Non)transparency of Space”. Bulletin of the American Astronomical Society. 31 (31): 1479. Bibcode:1999AAS…195.7409T.
38. ^ Jump up to:a b Kepple & Sanner 1998, p. 18
39. ^ Jump up to:a b “The Large Magellanic Cloud, LMC”. Observatoire de Paris. March 11, 2004. Archived from the original on June 22, 2017.
40. ^ “Abd-al-Rahman Al Sufi (December 7, 903 – May 25, 986 A.D.)”. Observatoire de Paris. Archived from the original on April 16, 2007. Retrieved April 19, 2007.
41. ^ Gordon, Kurtiss J. “History of our Understanding of a Spiral Galaxy: Messier 33”. Archived from the original on January 25, 2021. Retrieved June 11, 2018.
42. ^ Kant, Immanuel, Universal Natural History and Theory of the Heavens (1755)
43. ^ See text quoted from Wright’s An original theory or new hypothesis of the Universe in Dyson, F. (1979). Disturbing the Universe. Pan Books. p. 245. ISBN 978-0-330-26324-5. Archived from the original on March 24, 2021. Retrieved July 25, 2018.
44. ^
“Parsonstown | The genius of the Parsons family | William Rosse” Archived March 24, 2021, at the Wayback Machine.
45. ^ Slipher, V. M. (1913). “The radial velocity of the Andromeda Nebula”. Lowell Observatory Bulletin. 1 (8): 56–57. Bibcode:1913LowOB…2…56S.
46. ^ Slipher, V. M. (1915).
“Spectrographic Observations of Nebulae”. Popular Astronomy. Vol. 23. pp. 21–24. Bibcode:1915PA…..23…21S.
47. ^ Curtis, H. D. (1988). “Novae in Spiral Nebulae and the Island Universe Theory”. Publications of the Astronomical Society of the Pacific. 100: 6. Bibcode:1988PASP..100….6C.
48. ^ Weaver, H. F. “Robert Julius Trumpler”. US National Academy of Sciences. Archived from the original on December 24, 2013. Retrieved January 5, 2007.
49. ^ Öpik, E. (1922).
“An estimate of the distance of the Andromeda Nebula”. The Astrophysical Journal. 55: 406. Bibcode:1922ApJ….55..406O. doi:10.1086/142680.
50. ^ Hubble, E. P. (1929). “A spiral nebula as a stellar system, Messier 31”. The Astrophysical Journal. 69: 103–158. Bibcode:1929ApJ….69..103H. doi:10.1086/143167.
51. ^
Sandage, A. (1989). “Edwin Hubble, 1889–1953”. Journal of the Royal Astronomical Society of Canada. 83 (6): 351–362. Bibcode:1989JRASC..83..351S. Archived from the original on May 30, 2012. Retrieved January 8, 2007.
52. ^ Tenn, J.
“Hendrik Christoffel van de Hulst”. Sonoma State University. Archived from the original on May 29, 2012. Retrieved January 5, 2007.
53. ^ López-Corredoira, M.; et al. (2001). “Searching for the in-plane Galactic bar and ring in DENIS”. Astronomy and Astrophysics. 373 (1): 139–152.
arXiv:astro-ph/0104307. Bibcode:2001A&A…373..139L. doi:10.1051/0004-6361:20010560. S2CID 18399375.
54. ^ Rubin, V. C. (1983). “Dark matter in spiral galaxies”. Scientific American. Vol. 248, no. 6. pp. 96–106. Bibcode:1983SciAm.248f..96R. doi:10.1038/scientificamerican0683-96.
55. ^
Rubin, V. C. (2000). “One Hundred Years of Rotating Galaxies”. Publications of the Astronomical Society of the Pacific. 112 (772): 747–750. Bibcode:2000PASP..112..747R. doi:10.1086/316573.
56. ^
“Observable Universe contains ten times more galaxies than previously thought”. Archived from the original on December 23, 2020. Retrieved October 17, 2016.
57. ^ “Hubble Rules Out a Leading Explanation for Dark Matter”. Hubble News Desk. October 17, 1994. Archived from the original on August 1, 2012.
Retrieved January 8, 2007.
58. ^ “How many galaxies are there?”. NASA. November 27, 2002. Archived from the original on July 11, 2012. Retrieved January 8, 2007.
59. ^ Kraan-Korteweg, R. C.; Juraszek, S. (2000).
“Mapping the hidden Universe: The galaxy distribution in the Zone of Avoidance”. Publications of the Astronomical Society of Australia. 17 (1): 6–12. arXiv:astro-ph/9910572. Bibcode:2000PASA…17….6K. doi:10.1071/AS00006. S2CID 17900483.
60. ^ Lauer, Tod R.; Postman, Marc; Weaver, Harold A.; Spencer, John R.; Stern, S.
Alan; Buie, Marc W.; Durda, Daniel D.; Lisse, Carey M.; Poppe, A. R.; Binzel, Richard P.; Britt, Daniel T.; Buratti, Bonnie J.; Cheng, Andrew F.; Grundy, W. M.; Horányi, Mihaly; Kavelaars, J. J.; Linscott, Ivan R.; McKinnon, William B.; Moore, Jeffrey
M.; Núñez, J. I.; Olkin, Catherine B.; Parker, Joel W.; Porter, Simon B.; Reuter, Dennis C.; Robbins, Stuart J.; Schenk, Paul; Showalter, Mark R.; Singer, Kelsi N.; Verbiscer, Anne J.; Young, Leslie A. (January 11, 2021).
“New Horizons Observations of the Cosmic Optical Background”. The Astrophysical Journal. 906 (2): 77. arXiv:2011.03052. Bibcode:2021ApJ…906…77L. doi:10.3847/1538-4357/abc881. hdl:1721.1/133770. ISSN 1538-4357. S2CID 226277978. Retrieved January 15, 2021.
61. ^
“New Horizons spacecraft answers the question: How dark is space?”. Archived from the original on January 15, 2021. Retrieved January 15, 2021.
62. ^ Barstow, M. A. (2005). “Elliptical Galaxies”. Leicester University Physics Department. Archived from the original on July 29, 2012. Retrieved June 8,
63. ^ “Galaxies”. Cornell University. October 20, 2005. Archived from the original on June 29, 2014. Retrieved August 10, 2006.
64. ^ “Galactic onion”. Archived from the original on August 6, 2020. Retrieved May 11,
65. ^ Williams, M. J.; Bureau, M.; Cappellari, M. (2010). “Kinematic constraints on the stellar and dark matter content of spiral and S0 galaxies”. Monthly Notices of the Royal Astronomical Society. 400 (4): 1665–1689. arXiv:0909.0680. Bibcode:2009MNRAS.400.1665W.
doi:10.1111/j.1365-2966.2009.15582.x. S2CID 17940107.
66. ^ Smith, G. (March 6, 2000). “Galaxies — The Spiral Nebulae”. University of California, San Diego Center for Astrophysics & Space Sciences. Archived from the original on July 10, 2012. Retrieved
November 30, 2006.
67. ^ Van den Bergh 1998, p. 17
68. ^ “Fat or flat: Getting galaxies into shape” Archived March 24, 2021, at the Wayback Machine. February 2014
69. ^ Bertin & Lin 1996, pp. 65–85
70. ^ Belkora 2003, p. 355
71. ^
Eskridge, P. B.; Frogel, J. A. (1999). “What is the True Fraction of Barred Spiral Galaxies?”. Astrophysics and Space Science. 269/270: 427–430. Bibcode:1999Ap&SS.269..427E. doi:10.1023/A:1017025820201. S2CID 189840251.
72. ^ Bournaud, F.; Combes,
F. (2002). “Gas accretion on spiral galaxies: Bar formation and renewal”. Astronomy and Astrophysics. 392 (1): 83–102. arXiv:astro-ph/0206273. Bibcode:2002A&A…392…83B. doi:10.1051/0004-6361:20020920. S2CID 17562844.
73. ^ Knapen, J. H.; Perez-Ramirez,
D.; Laine, S. (2002). “Circumnuclear regions in barred spiral galaxies — II. Relations to host galaxies”. Monthly Notices of the Royal Astronomical Society. 337 (3): 808–828. arXiv:astro-ph/0207258. Bibcode:2002MNRAS.337..808K. doi:10.1046/j.1365-8711.2002.05840.x.
S2CID 10845683.
74. ^ Alard, C. (2001). “Another bar in the Bulge”. Astronomy and Astrophysics Letters. 379 (2): L44–L47. arXiv:astro-ph/0110491. Bibcode:2001A&A…379L..44A. doi:10.1051/0004-6361:20011487. S2CID 18018228.
75. ^ Sanders, R. (January
9, 2006). “Milky Way galaxy is warped and vibrating like a drum”. UCBerkeley News. Archived from the original on January 18, 2014. Retrieved May 24, 2006.
76. ^ Bell, G. R.; Levine, S. E. (1997).
“Mass of the Milky Way and Dwarf Spheroidal Stream Membership”. Bulletin of the American Astronomical Society. 29 (2): 1384. Bibcode:1997AAS…19110806B.
77. ^ “We Just Discovered a New Type of Colossal Galaxy”. Futurism. March 21, 2016. Archived from the original on March 24, 2021. Retrieved March 21, 2016.
78. ^
Ogle, Patrick M.; Lanz, Lauranne; Nader, Cyril; Helou, George (January 1, 2016). “Superluminous Spiral Galaxies”. The Astrophysical Journal. 817 (2): 109. arXiv:1511.00659. Bibcode:2016ApJ…817..109O. doi:10.3847/0004-637X/817/2/109. ISSN 0004-637X.
S2CID 35287348.
79. ^ Gerber, R. A.; Lamb, S. A.; Balsara, D. S. (1994). “Ring Galaxy Evolution as a Function of “Intruder ” Mass”. Bulletin of the American Astronomical Society. 26: 911. Bibcode:1994AAS…184.3204G.
80. ^
“ISO unveils the hidden rings of Andromeda” (Press release). European Space Agency. October 14, 1998. Archived from the original on August 28, 1999. Retrieved May 24, 2006.
81. ^ “Spitzer Reveals What Edwin Hubble Missed”. Harvard-Smithsonian Center for Astrophysics. May 31, 2004. Archived
from the original on September 7, 2006. Retrieved December 6, 2006.
82. ^ Barstow, M. A. (2005). “Irregular Galaxies”. University of Leicester. Archived from the original on February 27, 2012. Retrieved December 5, 2006.
83. ^ Phillipps, S.; Drinkwater,
M. J.; Gregg, M. D.; Jones, J. B. (2001). “Ultracompact Dwarf Galaxies in the Fornax Cluster”. The Astrophysical Journal. 560 (1): 201–206. arXiv:astro-ph/0106377. Bibcode:2001ApJ…560..201P. doi:10.1086/322517. S2CID 18297376.
84. ^ Groshong,
K. (April 24, 2006). “Strange satellite galaxies revealed around Milky Way”. New Scientist. Archived from the original on July 2, 2015. Retrieved January 10, 2007.
85. ^ Schirber, M. (August 27, 2008). “No Slimming Down for Dwarf Galaxies”. ScienceNOW.
Archived from the original on May 30, 2020. Retrieved August 27, 2008.
86. ^ Jump up to:a b c “Galaxy Interactions”. University of Maryland Department of Astronomy. Archived from the original on May 9, 2006. Retrieved December 19, 2006.
87. ^
Jump up to:a b c “Interacting Galaxies”. Swinburne University. Archived from the original on July 7, 2012. Retrieved December 19, 2006.
88. ^ “Happy Sweet Sixteen, Hubble Telescope!”. NASA. April 24, 2006. Archived from the original on July 14,
2012. Retrieved August 10, 2006.
89. ^ Jump up to:a b “Starburst Galaxies”. Harvard-Smithsonian Center for Astrophysics. August 29, 2006. Archived from the original on March 16, 2019. Retrieved August 10, 2006.
90. ^ Kennicutt Jr., R. C.; et al.
(2005). Demographics and Host Galaxies of Starbursts. Starbursts: From 30 Doradus to Lyman Break Galaxies. Springer. p. 187. Bibcode:2005ASSL..329..187K. doi:10.1007/1-4020-3539-X_33. ISBN 978-1-4020-3538-8.
91. ^ Smith, G. (July 13, 2006).
“Starbursts & Colliding Galaxies”. University of California, San Diego Center for Astrophysics & Space Sciences. Archived from the original on July 7, 2012. Retrieved August 10, 2006.
92. ^ Keel, B. (September 2006). “Starburst Galaxies”. University of Alabama. Archived from the
original on June 4, 2012. Retrieved December 11, 2006.
93. ^ Jump up to:a b Keel, W. C. (2000). “Introducing Active Galactic Nuclei”. University of Alabama. Archived from the original on July 27, 2012. Retrieved December 6, 2006.
94. ^ Jump up
to:a b Lochner, J.; Gibb, M. “A Monster in the Middle”. NASA. Archived from the original on July 10, 2012. Retrieved December 20, 2006.
95. ^ Jump up to:a b Heckman, T. M. (1980).
“An optical and radio survey of the nuclei of bright galaxies — Activity in normal galactic nuclei”. Astronomy and Astrophysics. 87: 152–164. Bibcode:1980A&A….87..152H.
96. ^ Ho, L. C.; Filippenko, A. V.; Sargent, W. L. W. (1997). “A Search for “Dwarf ” Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies”. The Astrophysical
Journal. 487 (2): 568–578. arXiv:astro-ph/9704108. Bibcode:1997ApJ…487..568H. doi:10.1086/304638. S2CID 16742031.
97. ^ Peterson, Bradley M. (1997). An Introduction to Active Galactic Nuclei. Cambridge University Press. ISBN 978-0-521-47911-0.
98. ^
Jump up to:a b Beck, Rainer (2007). “Galactic magnetic fields”. Scholarpedia. Vol. 2. p. 2411. Bibcode:2007SchpJ…2.2411B. doi:10.4249/scholarpedia.2411.
99. ^ “Construction Secrets of a Galactic Metropolis”. ESO Press Release. Archived
from the original on March 24, 2021. Retrieved October 15, 2014.
100. ^ Jump up to:a b “Protogalaxies”. Harvard-Smithsonian Center for Astrophysics. November 18, 1999. Archived from the original on March 25, 2008. Retrieved January 10, 2007.
101. ^
Firmani, C.; Avila-Reese, V. (2003). “Physical processes behind the morphological Hubble sequence”. Revista Mexicana de Astronomía y Astrofísica. 17: 107–120. arXiv:astro-ph/0303543. Bibcode:2003RMxAC..17..107F.
102. ^ McMahon, R. (2006).
“Astronomy: Dawn after the dark age”. Nature. 443 (7108): 151–2. Bibcode:2006Natur.443..151M. doi:10.1038/443151a. PMID 16971933. S2CID 28977650.
103. ^ Wall, Mike (December 12, 2012). “Ancient Galaxy May Be Most Distant Ever Seen”. Archived from the original on May 4,
2019. Retrieved December 12, 2012.
104. ^ “Cosmic Detectives”. The European Space Agency (ESA). April 2, 2013. Archived from the original on February 11, 2019. Retrieved April 15, 2013.
105. ^
“HubbleSite – NewsCenter – Astronomers Set a New Galaxy Distance Record (05/05/2015) – Introduction”. Archived from the original on December 9, 2016. Retrieved May 7, 2015.
106. ^ “This Galaxy Far, Far Away Is the Farthest One Yet Found”. May 5, 2015. Archived from the original on October 2, 2015. Retrieved May 7, 2015.
107. ^
“Astronomers unveil the farthest galaxy”. Archived from the original on September 11, 2017. Retrieved May 7, 2015.
108. ^ Overbye, Dennis (May 5, 2015). “Astronomers Measure Distance to Farthest Galaxy Yet”. The New York Times. ISSN 0362-4331. Archived from the original on April 13,
2019. Retrieved May 7, 2015.
109. ^ Oesch, P. A.; van Dokkum, P. G.; Illingworth, G. D.; Bouwens, R. J.; Momcheva, I.; Holden, B.; Roberts-Borsani, G. W.; Smit, R.; Franx, M. (February 18, 2015).
“A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE”. The Astrophysical Journal. 804 (2): L30. arXiv:1502.05399. Bibcode:2015ApJ…804L..30O. doi:10.1088/2041-8205/804/2/L30. S2CID 55115344.
110. ^ “Signatures of the Earliest Galaxies”. Archived from the original on August 6, 2020. Retrieved September
15, 2015.
111. ^ Eggen, O. J.; Lynden-Bell, D.; Sandage, A. R. (1962). “Evidence from the motions of old stars that the Galaxy collapsed”. The Astrophysical Journal. 136: 748. Bibcode:1962ApJ…136..748E. doi:10.1086/147433.
112. ^ Searle, L.;
Zinn, R. (1978). “Compositions of halo clusters and the formation of the galactic halo”. The Astrophysical Journal. 225 (1): 357–379. Bibcode:1978ApJ…225..357S. doi:10.1086/156499.
113. ^ Heger, A.; Woosley, S. E. (2002).
“The Nucleosynthetic Signature of Population III”. The Astrophysical Journal. 567 (1): 532–543. arXiv:astro-ph/0107037. Bibcode:2002ApJ…567..532H. doi:10.1086/338487. S2CID 16050642.
114. ^ Barkana, R.; Loeb, A. (2001).
“In the beginning: the first sources of light and the reionization of the Universe” (PDF). Physics Reports (Submitted manuscript). 349 (2): 125–238. arXiv:astro-ph/0010468. Bibcode:2001PhR…349..125B. doi:10.1016/S0370-1573(01)00019-9. S2CID 119094218. Archived (PDF) from the original on March 14, 2021. Retrieved July 25, 2018.
115. ^
Sobral, David; Matthee, Jorryt; Darvish, Behnam; Schaerer, Daniel; Mobasher, Bahram; Röttgering, Huub J. A.; Santos, Sérgio; Hemmati, Shoubaneh (June 4, 2015).
“Evidence for POPIII-like Stellar Populations in the Most Luminous LYMAN-α Emitters at the Epoch of Re-ionisation: Spectroscopic Confirmation”. The Astrophysical Journal. 808 (2): 139. arXiv:1504.01734. Bibcode:2015ApJ…808..139S. doi:10.1088/0004-637x/808/2/139. S2CID 18471887.
116. ^ Overbye, Dennis (June 17, 2015). “Traces of Earliest Stars That Enriched Cosmos Are Spied”. The New
York Times. Archived from the original on June 29, 2019. Retrieved June 17, 2015.
117. ^ “Simulations Show How Growing Black Holes Regulate Galaxy Formation”. Carnegie Mellon University. February 9, 2005. Archived from the original on June 4, 2012.
Retrieved January 7, 2007.
118. ^ Massey, R. (April 21, 2007). “Caught in the act; forming galaxies captured in the young Universe”. Royal Astronomical Society. Archived from the original on November 15, 2013. Retrieved April 20, 2007.
119. ^
Noguchi, M. (1999). “Early Evolution of Disk Galaxies: Formation of Bulges in Clumpy Young Galactic Disks”. The Astrophysical Journal. 514 (1): 77–95. arXiv:astro-ph/9806355. Bibcode:1999ApJ…514…77N. doi:10.1086/306932. S2CID 17963236.
120. ^
Baugh, C.; Frenk, C. (May 1999). “How are galaxies made?”. PhysicsWeb. Archived from the original on April 26, 2007. Retrieved January 16, 2007.
121. ^ Gonzalez, G. (1998). The Stellar Metallicity — Planet Connection. Brown dwarfs and extrasolar
planets: Proceedings of a workshop … p. 431. Bibcode:1998ASPC..134..431G.
122. ^ Moskowitz, Clara (September 25, 2012). “Hubble Telescope Reveals Farthest View Into Universe Ever”. Archived from the original on May 5, 2020. Retrieved
September 26, 2012.
123. ^ Conselice, C. J. (February 2007). “The Universe’s Invisible Hand”. Scientific American. Vol. 296, no. 2. pp. 35–41. Bibcode:2007SciAm.296b..34C. doi:10.1038/scientificamerican0207-34.
124. ^ Ford, H.; et al. (April
30, 2002). “The Mice (NGC 4676): Colliding Galaxies With Tails of Stars and Gas”. Hubble News Desk. Archived from the original on September 7, 2016. Retrieved May 8, 2007.
125. ^ Struck, C. (1999). “Galaxy Collisions”. Physics Reports. 321 (1–3):
1–137. arXiv:astro-ph/9908269. Bibcode:1999PhR…321….1S. doi:10.1016/S0370-1573(99)00030-7. S2CID 119369136.
126. ^ Wong, J. (April 14, 2000). “Astrophysicist maps out our own galaxy’s end”. University of Toronto. Archived from the original
on January 8, 2007. Retrieved January 11, 2007.
127. ^ Panter, B.; Jimenez, R.; Heavens, A. F.; Charlot, S. (2007). “The star formation histories of galaxies in the Sloan Digital Sky Survey”. Monthly Notices of the Royal Astronomical Society. 378
(4): 1550–1564. arXiv:astro-ph/0608531. Bibcode:2007MNRAS.378.1550P. doi:10.1111/j.1365-2966.2007.11909.x. S2CID 15174718.
128. ^ Kennicutt Jr., R. C.; Tamblyn, P.; Congdon, C. E. (1994). “Past and future star formation in disk galaxies”. The Astrophysical
Journal. 435 (1): 22–36. Bibcode:1994ApJ…435…22K. doi:10.1086/174790.
129. ^ Knapp, G. R. (1999). Star Formation in Early Type Galaxies. Star Formation in Early Type Galaxies. Vol. 163. Astronomical Society of the Pacific. p. 119. arXiv:astro-ph/9808266.
Bibcode:1999ASPC..163..119K. ISBN 978-1-886733-84-8. OCLC 41302839. Archived from the original on March 24, 2021. Retrieved July 25, 2018.
130. ^ Jump up to:a b Adams, Fred; Laughlin, Greg (July 13, 2006). “The Great Cosmic Battle”. Astronomical
Society of the Pacific. Archived from the original on July 31, 2012. Retrieved January 16, 2007.
131. ^ “Cosmic ‘Murder Mystery’ Solved: Galaxies Are ‘Strangled to Death'”. May 13, 2015. Archived from the original on March 24, 2021.
Retrieved May 14, 2015.
132. ^ Pobojewski, S. (January 21, 1997). “Physics offers glimpse into the dark side of the Universe”. University of Michigan. Archived from the original on June 4, 2012. Retrieved January 13, 2007.
133. ^ McKee, M. (June
7, 2005). “Galactic loners produce more stars”. New Scientist. Archived from the original on October 20, 2012. Retrieved January 15, 2007.
134. ^ “Groups & Clusters of Galaxies”. NASA/Chandra. Archived from the original on July 7, 2012. Retrieved
January 15, 2007.
135. ^ Ricker, P. “When Galaxy Clusters Collide”. San Diego Supercomputer Center. Archived from the original on August 5, 2012. Retrieved August 27, 2008.
136. ^ Dahlem, M. (November 24, 2006).
“Optical and radio survey of Southern Compact Groups of galaxies”. University of Birmingham Astrophysics and Space Research Group. Archived from the original on June 13, 2007. Retrieved January 15, 2007.
137. ^ Ponman, T. (February 25, 2005). “Galaxy Systems: Groups”. University of Birmingham Astrophysics and
Space Research Group. Archived from the original on February 15, 2009. Retrieved January 15, 2007.
138. ^ Girardi, M.; Giuricin, G. (2000). “The Observational Mass Function of Loose Galaxy Groups”. The Astrophysical Journal. 540 (1): 45–56. arXiv:astro-ph/0004149.
Bibcode:2000ApJ…540…45G. doi:10.1086/309314. S2CID 14059401.
139. ^ “Hubble Pinpoints Furthest Protocluster of Galaxies Ever Seen”. ESA/Hubble Press Release. Archived from the original on June 12, 2018. Retrieved January 22, 2015.
140. ^ Dubinski,
J. (1998). “The Origin of the Brightest Cluster Galaxies”. The Astrophysical Journal. 502 (2): 141–149. arXiv:astro-ph/9709102. Bibcode:1998ApJ…502..141D. doi:10.1086/305901. S2CID 3137328. Archived from the original on May 14, 2011. Retrieved January
16, 2007.
141. ^ “ATLASGAL Survey of Milky Way Completed”. Archived from the original on March 24, 2021. Retrieved March 7, 2016.
142. ^ Bahcall, N. A. (1988). “Large-scale structure in the Universe indicated by galaxy clusters”. Annual Review
of Astronomy and Astrophysics. 26 (1): 631–686. Bibcode:1988ARA&A..26..631B. doi:10.1146/annurev.aa.26.090188.003215.
143. ^ Mandolesi, N.; et al. (1986). “Large-scale homogeneity of the Universe measured by the microwave background”. Letters to
Nature. 319 (6056): 751–753. Bibcode:1986Natur.319..751M. doi:10.1038/319751a0. S2CID 4349689.
144. ^ Horváth, István; Bagoly, Zsolt; Hakkila, Jon; Tóth, L. Viktor (2015).
“New data support the existence of the Hercules-Corona Borealis Great Wall”. Astronomy & Astrophysics. 584: A48. arXiv:1510.01933. Bibcode:2015A&A…584A..48H. doi:10.1051/0004-6361/201424829. S2CID 56073380.
145. ^ Horváth, István; Bagoly, Zsolt; Hakkila, Jon; Tóth, L. Viktor (2014).
“Anomalies in the GRB spatial distribution”. Proceedings of Science: 78. arXiv:1507.05528. Bibcode:2014styd.confE..78H.
146. ^ Balazs, L. G.; Bagoly, Z.; Hakkila, J. E.; Horváth, I.; Kobori, J.; Racz, I.; Tóth, L. V. (2015). “A giant ring-like structure at 0.78<z<0.86 displayed by GRBs”.
Monthly Notices of the Royal Astronomical Society. 452 (3): 2236. arXiv:1507.00675. Bibcode:2015MNRAS.452.2236B. doi:10.1093/mnras/stv1421. S2CID 109936564.
147. ^ van den Bergh, S. (2000). “Updated Information on the Local Group”. Publications
of the Astronomical Society of the Pacific. 112 (770): 529–536. arXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. doi:10.1086/316548. S2CID 1805423.
148. ^ Tully, R. B. (1982). “The Local Supercluster”. The Astrophysical Journal. 257: 389–422.
Bibcode:1982ApJ…257..389T. doi:10.1086/159999.
149. ^ “Near, Mid & Far Infrared”. IPAC/NASA. Archived from the original on December 30, 2006. Retrieved January 2, 2007.
150. ^ “The Effects of Earth’s Upper Atmosphere on Radio Signals”. NASA.
Archived from the original on May 29, 2012. Retrieved August 10, 2006.
151. ^ “Giant Radio Telescope Imaging Could Make Dark Matter Visible”. ScienceDaily. December 14, 2006. Archived from the original on July 3, 2017. Retrieved January 2, 2007.
152. ^
“NASA Telescope Sees Black Hole Munch on a Star”. NASA. December 5, 2006. Archived from the original on June 4, 2012. Retrieved January 2, 2007.
153. ^ Dunn, R. “An Introduction to X-ray Astronomy”. Institute of Astronomy X-Ray Group. Archived from the original on July 17, 2012. Retrieved January
2, 2007.
154. ^ “Squabbling Galactic Siblings”. Archived from the original on July 26, 2021. Retrieved July 16, 2021.
155. ^ “Hubble Returns to Science Operations”. Archived from the original on July 19, 2021. Retrieved July 26, 2021.
156. ^
NASA (May 2, 2019). “Hubble astronomers assemble wide view of the evolving universe”. EurekAlert!. Archived from the original on March 24, 2021. Retrieved May 2, 2019.
2. “Unveiling the Secret of a Virgo Dwarf Galaxy”. ESO. May 3, 2000. Archived
from the original on January 9, 2009. Retrieved January 3, 2007.

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