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galaxies are vast collection of stars gas and dust, they come in a variety of shapes and sizes, the most familiar galaxy shape is a spiral pattern, traced out by bright stars and by dark dust lanes, some spiral galaxies have many spiral arms while others have just a couple. a good percentage of spiral galaxies have an elongated straight region across the middle, these are barred spiral galaxies all of these spiral arms are within a thin disc, resembling the shape of a pancake. in the center of the disk is a rounded bulge of stars, some bulges of stars are very small compared to the size of their disk. while others are quite large a galaxy, that is entirely this rounded shape is called an elliptical galaxy, elliptical galaxies are dominated by stars and generally have very little gas and dust, elliptical galaxies can appear roughly spherical or they can be rather elongated. the largest galaxies in the universe are giant elliptical galaxies found in the cores of large clusters of galaxies. on the other end of the scale dwarf elliptical galaxies can be found as small satellites around larger galaxies. while dwarf elliptical galaxies can have as few as tens of millions of stars, giant ellipticals can have as many as a trillion stars, other dwarf galaxies have no specific shape, these are irregular galaxies, irregular galaxies exhibit a wide variation in their shapes and their composition, many dwarf irregular x' have lots of gas dust and bright regions where stars are forming. it is important to note that there are many more dwarf galaxies elliptical and irregular then there are large galaxies in the universe. large irregular galaxies also exist but their shapes are due to the collisions and mergers between galaxies across the entire universe, there are about a hundred billion galaxies, they come in spiral elliptical and irregular shapes and their sizes range from dwarfs to Giants.



CREDITS:
Produced by the Space Telescope Science Institute, Office of Public Outreach
All images, illustrations, and videos courtesy of NASA, ESA, and STScI except:
• Messier 74 image courtesy of Gemini Observatory - GMOS Team;
• NGC 1232 image courtesy of ESO/IDA/Danish 1.5m/R. Gendler and A. Hornstrup;
• Messier 51 image courtesy of NASA, ESA, S. Beckwith (STScI), and the Hubble Heritage Team (STScI/AURA);
• NGC 1300 image courtesy of NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgement: P. Knezek (WIYN);
• NGC 891 image courtesy of Robert Gendler, NOAJ, HST/NASA, BYU (Michael Joner and David Laney);
• NGC 3982 image courtesy of NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgement: A. Riess (STScI);
• Sombrero Galaxy image courtesy of NASA and the Hubble Heritage Team (STScI/AURA);
• NGC 1132 image courtesy of NASA and the Hubble Heritage Team (STScI/AURA);
• Messier 87 image courtesy of Robert Lupton and the SDSS Consortium;
• NGC 4150 image courtesy of NASA, EAS, R.M. Crockett (University of Oxford, U.K.), S. Kaviraj (Imperial College London and University of Oxford, U.K.);
• Messier 31 image courtesy of Bill Schoening, Vanessa Harve/REU program/NOAO/AURA/NSF;
• NGC 1427a image courtesy of NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgement: M. Gregg (University of California-Davis and Institute for Geophysics and Planetary Physics, Lawrence Livermore National Lab)
• I Zwicky 18 image courtesy of NASA, ESA, Y. Izotov (Main Astronomical Observatory, Kyiv UA) and T. Thuan (University of Virginia);
• NGC 4449 image courtesy of NASA, ESA, A. Aloisi (STScI/ESA), and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration;
• NGC 6240 image courtesy of NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)
• Messier 101 Hubble image courtesy of NASA and ESA; Acknowledgement: K.D. Kuntz (GSFC), F. Bresolin (University of Hawaii), J. Trauger (JPL), J. Mould (NOAO), Y.H. Chu (University of Illinois, Urbana); CFHT image courtesy of Canada-France-Hawaii Telescope/ J.C. Cuillandre/Coelum; NOAO image courtesy of G. Jacoby, B. Bohannan, M. Hanna/NOAO/AURA/NSF
• NGC 5982 image courtesy of T.A. Rector (University of Alaska, Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF)
• Small Magellanic Cloud image courtesy of NOAO/AURA/NSF

Written by Frank Summers
Designed by Marc Lussier