Irregular galaxy

Large Magellanic Cloud

Irregular galaxies , i.e. H. irregular galaxies , have neither clear structures nor symmetries:

• no excellent plane of symmetry
• accordingly, there are no spiral arms as in the spiral galaxies .
• They also do not have an elliptical shape like elliptical galaxies .
• They also lack a galaxy core.

Instead, irregular galaxies have several, irregularly distributed smaller densities. They can therefore not be included in the Hubble sequence , but rather form a special class, which is abbreviated as Ir or Irr . The best-known representatives of this type are the two magellanic clouds .

properties

Irregular galaxies have much less mass (between 700 million and 130 billion solar masses ) and a significantly lower gravitational field than regular galaxies, and on average they are less luminous . Irregular galaxies make up about 4 percent of all galaxies.

Irregular galaxies contain a lot of gas and dust and young stars that are very irregularly distributed. Most of the older stars are often distributed in a more regular, flattened structure and rotate as in spiral galaxies.

Emergence

NGC 1569 , an irregular dwarf galaxy with violent starbursts

In principle, several different development scenarios are known / imaginable:

• Primordial gas falls into a relatively shallow gravitational potential well created by dark matter and forms distributed first chaotic small star formation regions ( Blue compact dwarf galaxies : blue compact dwarf galaxies ).
• Regular galaxies in galaxy clusters are deformed by the tidal forces of larger galaxies.
• Two smaller galaxies merge .
• The previously regular structure is severely deformed by an extreme local star formation phase within a galaxy.

Individual evidence

1. ↑ http://www.astro.uni-bonn.de/~geffert/prakt01I/galaxien.html#24 ( Memento from August 6, 2007 in the Internet Archive )
2. ↑ http://www.br-online.de/wissen-bildung/spacenight/sterngucker/deepsky/galaxietypen.html#elliptische

literature

• Joachim Krautter, Erwin Sedlmayr, Karl Schaifers : Meyers Handbuch Weltall . 7th edition. Bibliographisches Institut, Mannheim 1994, ISBN 978-3-411-07757-1 , p. 469, 470 .

Web links

• What are irregular galaxies? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Oct 26, 2005.