Classification and Characteristics of Galaxies, Essay Example

Like animals and plants are classified in biology, galaxies too have classifications and defining characteristics, which help scientists to identify and study them. “Hubble divided galaxies into two principal categories Elliptical and Spiral, with a third “Irregular” category left to catch those galaxies which defied regular classification” (Galaxies – The Spiral Nebulae, 2000). In this paper I will give a list of the known types of galaxies and describe their features.

Spiral galaxies are thought to be the first galaxies to form out of a cloud of material after the overall construction of the universe. As the cloud was steadily collapsing, it spun up, forcing some of the material to shape a disk. The defining feature of the spiral galaxies is their spiral ‘arms’ made of luminous stars. There is the same amount of matter between the arms as there is in the arms, but the starts outside the arms are not so luminous, and as a result, are not so noticeable.

Barred spirals are formed much like the spiral galaxies. These galaxies are recognized by the ‘bar’, a highly centered concentration of gas. Some researchers state that these regions form when the two galaxies collide or miss each other while drifting in the open space.

Elliptical galaxies do not have spiral arms. These galaxies contain neither free gas nor dust to form new stars, therefore, they are made of old, low-mass stars.

Lenticular galaxies are spiral galaxies that do not have the spiral configuration. These galaxies look much like elliptical ones, as far as they also contain old stars, with the building matter all used up.

Irregular galaxies are simply galaxies that cannot fit into other classifications. These galaxies often look distorted and weirdly shaped, due to the constant formation of new stars in them.

References

Galaxies – The Spiral Nebulae. (2000, March). Center for Astrophysics and Space Sciences. Retrieved February 15, 2009, from http://cass.ucsd.edu/public/tutorial/Galaxies.html