The universe we know has great dimensions and there is not only the galaxy in which we live. There are numerous galaxies and not all are the same. There are galaxies of different shapes and sizes, from giants to dwarfs. Edwin Hubble made a classification of the galaxies in 1936 to be able to separate which are the different types of galaxies according to their shapes and their visual appearance. All this classification has been expanded over time, but today it is still in force.
In this article we are going to tell you what are the different types of galaxies that exist and what are their main characteristics.
Classification of the different types of galaxies
Galaxies are classified into different types. We can see the main types of galaxies like elliptical, lenticular, spiral, and irregular. Since Edwin Hubble thought that there was an evolution and development in galaxies from elliptical lenticular wings and from these to spirals, he made what is known as the Hubble sequence. Since irregular galaxies do not fit with the rest they do not enter into any kind of sequences.
We know that a galaxy is an entity or composite object made up of a large number of stars and interstellar matter that is held together each other by their own action of gravity. By having its own action of gravity on the components that make up the galaxy they remain isolated from space. There are an estimated 100.000 billion galaxies in the known universe. However, surely this number increases with the passage of time thanks to the advancement of technology. All this number of galaxies are grouped into clusters normally.
We know that the Milky Way is our home and another 200 billion stars and is what gives the galaxy its name. In addition, it is important to know the dimensions of the observable universe to better understand the vast number of galaxies that exist. You can also read more about how many galaxies are there in the universe to get a better idea of the size of the cosmos.
Types of galaxies
We are going to classify the different types of galaxies that exist and to name their main characteristics.
Elliptical galaxies
It is shaped like an ellipse and can have a greater or lesser eccentricity. They are usually galaxies that They are named with the letter E followed by a number that goes between 0 and 7. The number is presented to be able to point out the eccentricity liver of the galaxy. These types of galaxies are divided into 8 different types named from E0 to E7. It can be said that the former is practically spherical and has no eccentricity, while the latter has a high eccentricity and a more elongated appearance.
Elliptical galaxies have very little gas and dust and virtually no interstellar matter. With few young stars, most of these stars are old. Almost most of them revolve around the nucleus in a messy and random way. We can find a great variety of sizes from giant to dwarf. The largest galaxies are elliptical since, when galaxies hatch they merge to form enormous elliptical galaxies. These are, without a doubt, of great interest for the study of the types of stars that compose them. In this regard, you can also consult another article on galaxies in general for more information.
Lenticular galaxies
Only one type of galaxies that are classified between ellipticals and spirals. They are dominated by an almost spherical nucleus made up of old stars, as is the case with ellipticals. They also have a disk of stars and gas around them just like spirals. But it has no spiral arms. It doesn't have much more interstellar and hardly any new star formation.
Lenticular galaxies can have a roughly spherical nucleus or a central band of stars. A barred lenticular galaxy is called a SO, and a barred lenticular galaxy is called a SOB. These types of galaxies are essential for understanding the formation of spiral galaxies over time, as well as for the study of the galaxies in the Laniakea cluster.
Spiral galaxies
These types of galaxies are formed by a shower of old stars. This core has a rotating disk of stars and lots of interstellar material that is orbiting around this nucleus of old stars. The rotating disk of stars is known to be made up of spiral arms that extend from the central nucleus. In these arms we have both young stars, more direct stars of the main sequence. These arms are what makes this type of galaxy called a spiral.
The spiral arms have a continuous star formation. If we analyze the disk we can find that there is a halo with globular clusters and scattered stars of different types. Among them we find old stars. This type of galaxy is designated with a letter S followed by another lowercase letter that can be a, b, c or d. This varies depending on the size and appearance of the core and arms. If we take a galaxy Sa we will see that they have a large nucleus in size with respect to the arms. These arms will find the core tighter as they are also smaller.
On the other hand, we have Sd galaxies, which have a smaller nucleus but larger, more widely dispersed arms. In many types of spiral galaxies, we can see a straight bar on both sides of the nucleus from which the spiral arms emerge. This type of galaxy, like the previous one, is known as barred spiral galaxies. They are usually denoted with SB and the letter, just like the previous one. This combination of letters has the same meaning as unbarred spirals. If you'd like to delve deeper into this topic, you can read more about the sombrero galaxy which is a clear example of a spiral galaxy, and it is also interesting to explore some very beautiful galaxies that can be observed.
Irregular galaxies
As we mentioned before, irregular galaxies lack any defined structure or symmetry. Therefore, it's more difficult to fit them into any galaxy sequence. They don't have an elliptical shape, nor do they fit into the Hubble sequence. They are smaller galaxies with a large amount of interstellar gas and dust.
Their nomenclature is designated with Irr and they are classified into two types. The Irr I or Magellanic type and the Irr IIThe former are the most common and are formed by old stars with very low luminosity. These galaxies have no nucleus. The latter are more active and are formed by young stars. They usually form through the interaction between the gravitational force of nearby galaxies. They can also arise from the collision of two galaxies. For a better understanding, you can read more about irregular galaxies.
I hope that with this information you can learn more about the types of galaxies.