Galaxy

From TinWiki.org

A galaxy is an accumulation or mass of interstellar gas, stars, dust, dark energy, and dark matter. Galaxies are enormous in size compared to a star or even a solar system, usually comprising of billions of stars.

[[1]] The M101 galaxy - a classic spiral galaxy.

1 Types of Galaxies
2 Galactic Collisions
3 The Nucleus
4 External Links

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Types of Galaxies

The categories for each of the three galaxies are solely based on their shape/form.

Spiral-Most galaxies in the universe are spirals and this shape is considered the norm; our very own Milky Way is spiral galaxy and about average in size. They are about 100,000 light years in diameter and resemble a flat disk. Spiral galaxies have arms (also called spirals), made up of dust and stars.

Elliptical-These are spheres or globs of stars that vary quite a bit in size and luminosity. There is hardly in cosmic dust in these types of galaxies and may not have a distinguishable nucleus. Also, the stars are older in elliptical galaxies than that of spirals. [[2]]

Irregular-Are very rare and don't exhibit qualities of spiral of elliptical galaxies and usually created by galaxies colliding.

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Galactic Collisions

These very rare events are massive collisions between two galaxies which result in one deformed galaxy - an irregular. When they collide, gravity brings them together to bind to each other and the centers merge. The Andromeda galaxy, or closest neighbor will eventually collide with ours, but that will be after the our Sun has turned into a red giant and engulfed the entire earth.

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The Nucleus

The center of almost all galaxies known to date have a super-massive black hole residing in them. The cause for these immensely large black holes is still a bit of a mystery, but some theories include the accumulation of many star-sized black holes in the history of a galaxy or each galaxy in the early universe formed around black holes, which added matter to the clump of dust to eventually create a massive galaxy.

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