Irregular galaxy

Irregular galaxies, ie irregular galaxies do not have excellent symmetry plane, corresponding to lack spiral arms as in the spiral galaxies. They also have no elliptical shape as elliptical galaxies. Also they lack a galaxy core, they have instead several irregularly distributed small condensations.

Properties

Irregular galaxies have much less mass ( between 700 million and 130 billion solar masses ) and a significantly lower gravitational potential than regular galaxies. Unlike them, show up at irregular galaxies neither clear nor structures symmetries. They can therefore not be classified in the Hubble sequence, but form a special class, with IR or Irr (English ) will be abbreviated.

They are on average fainter than the other types of galaxies. The best known representatives of this type are the two Magellanic Clouds.

Irregular galaxies contain a lot of gas and dust and young stars. The young stars are distributed very irregularly, often most of the older stars are distributed in a more regular, flattened structure and rotate as in spiral galaxies. Irregular galaxies make up about 4 percent of all galaxies.

Formation

There are basically several different development scenarios known / imagined:

• Primordial gas falling into a relatively flat created by dark matter gravitational potential well and is distributed first chaotic small star-forming regions (BCD blue compact dwarf galaxies)
• Regular galaxies in galaxy clusters are deformed by larger galaxies by tidal forces, and form irregular structures
• While two smaller galaxies merge, it forms an irregular galaxy
• With extreme local star formation phase within a galaxy previously regular structure is strongly deformed