Galaxies are huge containers of stars, whose diameter can be hundreds of thousands of light years, and as real islands in the universe are located in space at enormous distances (in billion) from each other. A separate single immense amount of intergalactic dust and interstellar material extremely rarefied (Evans, 1998).
The Milky Way Galaxy
The Milky Way is the galaxy where our Solar System together with at least 200 billion other stars, planets, thousands of clusters and nebulae, including almost all the Messier objects that are themselves galaxies (Bournaud, 2002). As a galaxy, the Milky Way is a giant with a mass between 750 and 1,000 billion solar masses and a diameter of about 100,000 light years. Radio astronomy research on the distribution of hydrogen clouds have revealed that our galaxy is of type Sb and Sc in the Hubble classification. It is not yet clear whether or not a structure is crossed, in the case would be type SB. The Milky Way belongs to the Local Group, a small group of three large and over thirty small galaxies, which occupies the second position for size but for the first mass.
Structure of the Galaxy
It belongs to the group of spiral galaxies and is composed of hundreds of billions of stars, interstellar gas and dust. It is shaped like a flattened disc with a diameter of 100 thousand light years, at whose center is the nucleus surrounded by filaments that are called spiral arms. Horizontally along the equatorial plane of the dark clouds which are apparently divided into two hemispheres (Rubin, 2000).
The core is composed of stars and star clusters whose birth dates back to the formative period of the same galaxy. It is located towards the constellation of Sagittarius, and was traced only by the abundance of the emitted radiation, since his vision is to us hidden by dark clouds. The disk is instead is composed largely of clouds of dust, interstellar gas and young stars and luminous blue. All around a halo composed of matter at low density, almost verging on absolute vacuum, and globular clusters.
Studies on the movements of the stars in the Milky Way indicate that it has a total mass equal to about 200 billion solar masses, considerably greater than that assessed by the visible matter. Astronomers believe therefore that the Milky Way is surrounded by an enormous region that contains dark matter. Recent hypothesis also suggests that our galaxy is classified as a barred spiral (Evans, 1998). ...