Irregular galaxies lack a regular structure or rotation and can be classified by unusual features. They make up 3-25% of galaxies and have three classifications: Irr-1, Irr-2, and irregular dwarf. They tend to have a weight of 108-1010 solar masses, diameters of 1-10 kiloparsecs, and high amounts of gas and dust. They can form from collisions or young galaxies. The Large Magellanic Cloud is an example of an irregular galaxy with high amounts of gas and dust and an irregular shape possibly caused by a collision or the Milky Way’s gravitational forces.
An irregular galaxy typically refers to a galaxy that has no regular structure or shape, meaning that it has little or no symmetry in its rotation. Irregular galaxies can also be classified according to some unusual feature that makes them different. This can include features such as a low surface brightness or strange gas flows emanating from its core. Scientists estimate that irregular galaxies make up 3% to 25% of the galaxies in the universe.
Based on the standard Hubble sequence, galaxies are classified according to three types of rotation: elliptical, spiral and lenticular. An irregular galaxy has none of these rotations. Consequently, it is sometimes referred to as the fourth type of galaxy.
There are generally three classifications of irregular galaxies. Type Irr-1 usually has some kind of standard structure, but not enough to be considered part of the Hubble sequence. The Irr-2 type has no standard movement and often has a chaotic structure. The third type is known as an irregular dwarf galaxy. This galaxy has low levels of metallicity, meaning it is largely composed of the chemical elements of hydrogen and helium. Since scientists believe that galaxies were made almost entirely of hydrogen at the time of the Big Bang, this could suggest that irregular dwarf galaxies are among the oldest in the universe.
Irregular galaxies tend to share some common characteristics. They generally have a weight ranging from 108 to 1010 solar masses. Their diameters tend to be between 1 and 10 kiloparsecs. Its blue magnitude – a measure of apparent visual magnitude – can range from -13 to -20. Many irregular galaxies are also distinguished by large amounts of gas and dust.
There are many ways an irregular galaxy can form. For example, one may result from a collision of galaxies. When this happens, the gravitational forces between separate galaxies interact, causing an erratic type of rotation. A young galaxy may also take on an irregular shape, suggesting that it has not yet achieved a symmetrical rotation.
Some irregular galaxies that have been identified include the Large Magellanic Cloud (LMC). The LMC is thought to be the third closest galaxy to the Milky Way. It is located between the constellations Dorado and Mensa, at a distance of 163,000 light-years from Earth. Scientists speculate that its irregular shape is the result of a collision of galaxies or that the gravitational forces of the Milky Way are affecting its rotation.
The LMC also has high amounts of gas and dust, which is common to an irregular galaxy. Part of the LMC is the Tarantula Nebula, a very active region for star formation. However, no scientific connections have been established between irregular galaxies and the possibility of forming stars.
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