Interstellar Inquiry #05: Galaxies Kaylen 25-26

Edwin Hubble invented a classification of galaxies and grouped them into four classes: spirals, barred spirals, ellipticals and irregulars.

He classified spiral and barred spiral galaxies further according to the size of their central bulge and the texture of their arms. The spiral arms can be wound tightly or loosely. Barred spirals sport ribbons of stars, gas, and dust that cut across their centers. Scientists think the presence of a bar indicates that a galaxy has reached full maturity. Older stars are found in the central bulge and younger stars are found in the spiral arms.

Elliptical galaxies look roughly egg-shaped and are relatively featureless. Apparent shapes range from almost circular (E0) to quite elliptical (E6) - these have the long axis four times the short axis. They contain very little gas and dust and primarily contain older stars. Scientists think elliptical galaxies originate from collisions and mergers with spirals.

Irregular galaxies do not fit into either category and have no defined shape. Scientists believe irregulars may the result of the gravitational pull of a neighboring galaxy or the result of a galactic collision. They can have a mix of old and young stars with a large amount of gas and dust necessary for forming new stars. They are believed to form due to gravitational attraction to a larger galaxy or by collision with another galaxy.