We know that there are different types of galaxies according to their formation and morphology. The composition of each of the galaxies is different and this makes it have unique characteristics. Today we are going to talk about irregular galaxies. It is a conglomeration of stars, planets, gas, dust and matter that are united by the force of gravity but visually lack a type of organization.
In this article we are going to tell you all the characteristics, formation and evolution of irregular galaxies.
Key features
Irregular galaxies are known to be those that do not have a visual organization. Studies estimate that approximately 15% of galaxies are irregular. Unlike galaxies such as the Milky Way and Andromeda that have a nucleus, a disk and some well-defined spiral arms, there are galaxies that do not have any type of symmetry or structure. Some of them have incipient bars or arms. But it is not a definite morphology.
The lack of organization that exists in irregular galaxies is attributed to several causes. One of the most common causes used to explain the formation of this type of galaxy is that there was a colossal explosionThe colossal explosion took place at the core of the galaxy and caused fragmentation is the dispersion of almost all content without losing all cohesion. In irregular galaxies you can find a deformation due to gravity exerted by some other neighboring galaxy that is larger.
We know that our galaxy, being spiral-shaped and large in size, has managed to distort two tiny galaxies known as the Magellanic Clouds. It has been suggested that these two small galaxies are merging with our own. In the distant future, it is possible that all this matter they contain will become part of the Milky Way. To learn more about these fascinating galaxies, you can consult the article on the magellanic cloud.
There is another irregular galaxy well known for being very bright. It's about the Cigar galaxy. It is a type of galaxy that is very rich in interstellar matter and in its interior the stars are forming at an accelerated rate. When they are young, the stars are blue and very bright, which explains the extraordinary brightness of this irregular-type galaxy.
Shapes and description of irregular galaxies
One of the characteristics that distinguishes irregular galaxies from other galaxies is their luminosity. This luminosity comes from the energy emitted per second by the galaxy at all frequencies and is proportional to the number of stars it contains. Irregular galaxies usually have a large number of stars, making them very luminous.
The color that galaxies have is related to the stellar populationThere are two types of stellar populations. Stars belonging to stellar population I are those that are young and dominated by heavier elements such as helium. On the other hand, in population II there are some elements of low metallicity and are considered to be older stars.
In the red sequence of the stars we see that galaxies appear with little or no stellar genesis. This type of galaxy category encompasses almost all elliptical galaxies. In contrast, galaxies with a high rate of star formation are found in the bluest zone. Among these galaxies that are full of new star formation we find the aforementioned Cigar Galaxy.
The greenest zone is a transition region where galaxies that have both young and old stellar populations meet. We can say that the Milky Way and Andromeda are examples of these galaxies that contain of the two stellar populations. These types of irregular galaxies are quite interesting to explore because they are the bluest of all. Although they don't have a distinctive shape, they do have a center. The highest stellar birth rates are found in the centers of these galaxies. Irregular galaxies are typically considered the youngest.
Types of irregular galaxies
Edwin Hubble was an astronomer who was in charge of classifying the different galaxies according to their apparent shape. After analyzing many photographic plates with the galaxies he was able to establish the basic patterns and the different types of galaxies. We have elliptical, lenticular, barred spiral, spiral, and irregular galaxies. Irregular ones are those that do not have any kind of apparent shape. Most of the galaxies that exist in the universe are of the elliptical or spiral type.
As we have learned about the galaxies, the classification has been expanded to be able to classify all these categories that do not meet a specific form. Here we find type I and II irregular galaxies. Although with some limitations, Edwin Hubble's scheme is of great help in establishing the characteristics and properties of these irregular galaxies. We are going to describe what are the characteristics of each type:
- Type I irregular galaxies: are those in which the original Hubble sequence appears, such as Magellanic cloud-type galaxies. It can be considered that they are a mixture between spiral galaxies that have not fully developed the structure or that have a rudimentary structure.
- Type II irregular galaxies: are those that are composed of very old and red stars. Normally, these stars tend to have less luminosity and they are galaxies as matter is already diffuse and they do not have any shape.
We see the example of the Magellanic cloud. They are two irregular galaxies. The large Magellanic cloud is 180.000 light-years away, while the small one is 210.000 light-years away. They are one of the few galaxies, next to Andromeda, that can be seen without the need for a telescope or very advanced technology.
I hope that with this information you can learn more about irregular galaxies and their characteristics.