Astronomy

Galaxies Types and Classifications



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In the process of exploring the universe, the Hubble telescope, in an 11.6 day period, observed 10,000 galaxies. This brief peek into the unknown, confirmed what we already knew, that the number of galaxies are endless, and, that they come  in many shapes, and various colors.

Back home, our own galaxy, the Milky Way, has a spiral shape, in which its billions of stars are held together by gravity. More than two thirds of the known galaxies have this same shape, and in the center, most astronomers believe, lies the infamous supermassive black hole. The presence of this black hole has been determined due to the fact that objects close to the center of the galaxy are orbiting at an accelerated rate of speed, indicating that something unseen is causing an immense gravitational pull.

As for the formation of these galaxies, there are two possibilities. One is that particles formed stars, then clusters, then galaxies. The other is that there was one giant formation that split apart to form individual galaxies.

Edwin Hubble classified galaxies as elliptical, spiral, lenticular and irregular. In an effort to be more specific when identifying various forms, he also devised subcategories, identifying various elliptical galaxies according to how flat they look, and spiral galaxies on the basis of how bright or large their central areas are. They can also be categorized by the shape of the “arms” that extend out from the central region and how compact they are in relation to the rest of the galaxy. Disks with no spiral “arms” out from the center are called lenticular, and irregular galaxies include those that do not fit any of the other categories.

Spiral galaxies have a bulge in the center of the galaxy, a disk, that contains gas, dust and stars, and a halo, which consists of older stars and globular clusters. The disk is the part of the galaxy that forms the “arms” of the spiral galaxy.

Elliptical galaxies appear to be somewhat oval in shape and are classified by the degree of elongation.

Irregular galaxies can take on almost any shape and sometimes appear as merely long strings of light. They may also be the result of galaxies that are in the process of merging.

No doubt, considering the fact that there are literally billions of galaxies in the universe, science will discover more varieties in the future. Every galaxy that is discovered gives us new insight into the formation of our own.



    



"Galaxies." NASA Science. Web. 15 Feb. 2011. http://science.nasa.gov/astrophysics/focus-areas/what-are-galaxies/.

"Galaxy Classification." Web. 15 Feb. 2011. <http://astro.wku.edu/astr106/galaxy.html>.

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