Thursday, January 1, 2009

Types of Galaxies

Galaxies are separated into three main types. These types are elliptical, spiral, and barred spiral. Elliptical galaxies, range from perfectly spherical to flattened discs. About 12% of the galaxies in the Universe are elliptical, and they can hold from hundred millions to trillions of stars and are commonly found at the centers of star clusters. Elliptical galaxies are older and very little star formation occurs in them, resulting in an old population of stars.

The next type, spiral galaxies, are centers of ongoing star formation, and are found in low density areas of galaxy clusters. Young and luminous stars illuminate bands in the galaxy, giving it a spiral appearance, but in reality, there are unseen stars outside the bands, forming what is called a galaxy halo.

These galaxies are almost identical to barred spiral galaxies and 2/3 of all spirals have bars. The structure is thought to help stellar formation.

Also, a quarter of all galaxies are irregular. They were formerly ellipticals or spirals, but were deformed by gravitational pull.

Images provided by Wikipedia.

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