The irregular galaxies do not have any definite shape as like spiral or elliptical galaxies. Irregular galaxies are very small and about one tenth of the mass of the milkyway galaxy. These galaxies contain both old and young stars and full of gas and dust due to that continues star formation is going in it. About 20% of all galaxies are irregular galaxies in the Universe.
Formation & Structure
At early stage some of the irregular galaxies were spiral or elliptical but due to uneven external gravitational attractions they were deformed into irregular galaxies.
They are rich in gas and dust but it is not true for Dwarf irregular galaxies. Dwarf irregular galaxies are as small as 3 kilo parsecs having 108 solar masses while larger irregular galaxies are about 10 kilo parsecs and 1010 solar masses. Due to lots of gas and dust, more star formation is going in it which makes them too bright. Irregular galaxies are distorted by neighbour galaxies. Small and large Magellanic clouds distorted by milky way is the best example.
Types of Irregular Galaxies
There are three main types of irregular Galaxies.
- Irr-I Galaxy : It has some structure but not enough to place into Hubble Sequence. Among them some have spiral structures which are called Sm galaxies while without spiral structures are called Im galaxies.
- Irr-II Galaxy : It has no specific structure which place into Hubble Squence.
- Dlrr Galaxy : These galaxies are dwarf galaxies with low metallicity and high level of gas.
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Authored by BK Suthar.
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