WHAT ARE IRREGULAR GALAXIES? - SCIENCE - 2025

The irregular galaxies are collections of stars that are not grouped following a typical pattern. While most galaxies are spiral, lenticular, or elliptical in shape, irregular galaxies always take on an amorphous appearance.

These types of galaxies are among the smallest in the entire Universe. They are usually made up of large amounts of gas and stardust. In general, a multitude of new stars are created inside it.

Irregular galaxies make up 20% of all galaxies in the known Universe. Two of the best known are the Magellanic Clouds, the large and the small, which orbit the Milky Way.

Types of irregular galaxies

Irregular galaxies can be classified into three types, based on their composition, their age, and their internal activity.

Irregular type I galaxies

This type of irregular galaxy is the more common of the two. These galaxies are made up of old, low luminosity stars. In general, they do not have a visible nucleus.

Most of them are classified as dwarf galaxies. They usually have a certain structure, although not enough to classify them within other types of galaxies.

Within this type of irregular galaxy, some scientists further classify them based on whether they exhibit features of spiral galaxies, ellipticals, or no structure at all.

Type II irregular galaxies

Type II irregular galaxies are made up of very young stars, and they are the ones with the most internal activity.

This type of galaxy does not present any type of shape. In general, they were created due to the interaction of strong gravitational forces, such as the collision of two larger galaxies.

This interaction was strong enough to erase all traces of their original structure.

Dwarf irregular galaxies

These irregular galaxies are mainly characterized by being much smaller than the other two types. Some may have a trace of structure, while others are totally amorphous.

There is no official consensus on how large an irregular galaxy must be to stop being considered a dwarf.

However, most of them share certain traits, such as that their stars are very young and there is not a great presence of complex elements within them.

Formation of irregular galaxies

The prevailing theory in astronomy is that irregular galaxies were formed by the interaction between two galaxies of another type. This interaction could have been a collision, which caused the stars of both formations to mix without a specific shape.

Another option is for a small galaxy to pass close to a larger one, and the effect of gravity from this second galaxy will deconstruct the first.

This is probably what happened to the Magellanic Clouds: as they passed close to the Milky Way, they lost their original structure and acquired the one we can observe today.

Most scientists agree that our own galaxy will suffer a similar fate in the next few million years.

At some point in the future, the Milky Way will collide with the Andromeda Galaxy, forming a new super-galaxy that will be irregular in shape.

References

1. "What is an irregular galaxy?" in: Cool Cosmos. Retrieved on: December 2, 2017 from Cool Cosmos: coolcosmos.ipac.caltech.edu.
2. "Irregular galaxies: Oddly shaped mysteries of the Universe" in: Thought Co. Retrieved on: December 2, 2017 from Thought Co: thoughtco.com.
3. "Irregular galaxies" in: Ecured. Retrieved on: December 2, 2017 from Ecured: ecured.cu.
4. "Irregular galaxy" in: Wikipedia. Retrieved on: December 2, 2017 from Wikipedia: en.wikipedia.org.
5. "Irregular galaxies" in: Escuelapedia. Retrieved on: December 2, 2017 from Escuelapedia: Escuelapedia.com.