Many people tend to point out the different types of galaxies that exist , as studying and determining the shapes of these diverse galaxies has been a recurring focus of study in thousands of explorations throughout history. In this article, I will show you the various types of galaxies that exist.
In this sense, discussing the origin of galaxy shapes is a question many of us might ask. However, scientists state that if all the gas coalesces into stars before it has time to form a disk, it becomes an elliptical galaxy. On the other hand, they define that if the gas has time to stabilize into a disk before all the stars coalesce, it becomes a spiral galaxy. If you'd like to learn more about the general characteristics of galaxies, you can read about the characteristics of galaxies.
On the other hand, some elliptical galaxies are made up of several galaxies that have merged. Research on distant galaxies shows that spiral galaxies were more common in the past than they are today; therefore, perhaps what were once spiral galaxies are now elliptical.
In any case, this is an actively explored site. The difficulty lies in the fact that most of the mass in galaxies is not referenced, making it very difficult for us to understand the dynamics of galaxy formation. You can also learn more about galaxy formation in the article that details how galaxies and stars form.
Inquiries of galaxy classifications
Discussing the different types of galaxies is a fascinating topic, as understanding their nature requires first investigating their classification. This classification relates to the representation of the galactic center (the arrangement of stars at the galaxy's core) and the disk (the distribution of the galaxy's spiral arms). If you'd like to learn more about the types of galaxies in the universe, keep reading.
Spirals, as their name suggests, have large disks and galactic centers of regular dimensions . Ellipticals are essentially just galactic centers without disks. Irregulars have neither symmetrical representations, nor a center, nor any perceptible disks.
What are the types of galaxies that exist?
According to the Hubble telescope, in the Milky Way we can find four main types of galaxies, which are:
1.Galaxy elliptical
One common type is the elliptical galaxy, which, as its name suggests, has the bright profile of an ellipse . These galaxies are sparse in gas and dust and are composed of old, yellow, low-metallicity stars—in other words, Population II stars. It is presumed that all large elliptical galaxies harbor a supermassive black hole at their galactic center. This is a fascinating topic that can be explored further in the context of how black holes form.
Characteristics of the elliptical galaxy
Elliptical galaxies vary greatly in brightness, mass, and volume, ranging from small dwarf spheroidal galaxies, with features resembling those of a globular cluster, but very rich in dark matter. Their common characteristics are:
Missing or insignificant angular instant.
Lack or negligible sum of interstellar matter ( gas and dust ), no young stars, lack of open heaps (except for exact inequalities like NGC 1275).
Center Light Gathering
In the "square" ones there is a lack of light gathering in their center while the "discoid" ones have more light gathering there.
Stellar populations
While the former are made up of old stars with a greater wealth of charged elements , in the latter there is little or no gain of such elements and their stars are younger (not much more).
radio wave sources
" Square " elliptical galaxies sometimes host sources that produce strong radio wave manifestations; in ring galaxies this is much rarer.
light blue
The former usually possess hot gas that can be discovered thanks to its manifestation of X-rays, especially in the largest ones; in the latter it is much rarer to have such gas.
Globular clusters and satellite galaxies
Large elliptical galaxies often possess a system of globular clusters, double nuclei, and a large number of satellite galaxies. One possible definition is galactic cannibalism, that is, the absorption of a smaller galaxy by a larger one; for example, our Milky Way is known to be "digesting" a couple of smaller galaxies today.
Origin of the elliptical galaxy
The usual image of elliptical galaxies presents them as galaxies where star creation ended after the initial explosion, now showing only old stars.
Recent research has found clusters of young, blue stars within some elliptical galaxies, alongside other constituents that can be formed by galaxy mergers. In this new view, an elliptical galaxy is the result of a long process where several smaller galaxies, of any type, collide and merge into a larger one. If you are interested in the impact these mergers have on galaxies, you can read the article on galaxy types and their formation.
There are three formulas in which an elliptical galaxy can be achieved from the collision between two previous galaxies: an encounter that astronomers frequently refer to as wet, in which there is abundant cold gas and a stellar outburst, and another referred to as dry, in which there is no gas or it is very scarce and therefore very little or no star formation.
The first type gives rise to a " disc-shaped " elliptical galaxy , and the second to a "square-shaped" elliptical galaxy. An excellent example of the second type, observed with the help of the Spitzer Telescope, is what is taking place in the galaxy cluster CL0958+4702, almost five billion light-years from our galaxy, where four large galaxies are merging together to form a much larger elliptical galaxy surrounded by a large halo made up of billions of stars ejected during melting.
The third path involves a spiral galaxy that has consumed all its gas through star formation or lost it through other means, becoming a lenticular galaxy. In this space, the collision and infiltration of smaller galaxies —which in the case of a spiral galaxy would have little consequence, as the resulting star formation would mitigate the damage tolerated by the galaxy's disk—ultimately destroy the disk of the lenticular galaxy, transforming it into an elliptical galaxy.
It is believed that all huge elliptical galaxies possess a supermassive black hole at their center.
2. Spiral galaxy
This type of galaxy has a nucleus or bulge made up of Population II stars (old, yellowish-orange, and with low metallicity), and a disk with a large amount of interstellar gas and dust. This leads to the formation of young, bluish, and highly metallic stars (Population I stars), increasing the number of spiral arms, which are created as shock waves due to the differential rotation of the entire galactic disk. You can find more information about how galaxies are formed in this interesting article.
Essentially, spiral galaxies are categorized into two large groups: Normal spirals and barred spirals (with a beam of stars running through the nucleus).
3. Lenticular Galaxy
What types of galaxies exist is a very common question, so I'll introduce you to another one: the lenticular galaxy . These galaxies have the shape of a nucleus with a disk, but without spiral arms. They are made up of old, low-metallic stars and little interstellar gas or dust. To better understand the difference between these and other types, see the article on lenticular galaxies.
They differ from elliptical galaxies in that they do have a disk, unlike those that only showed a more or less flattened nucleus. And they differ from spiral galaxies in that the disk is similar, that is, without stellar arms due to the cohesive forces generated by the interlocking motion of stars near the galactic nucleus.
Lenticular galaxies are often found in rich galaxy clusters, often as extensions of spiral galaxies. They appear to have once been spiral galaxies that lost their gas through friction with the heated intergalactic gas that fills intergalactic space , or through gravitational interactions with other galaxies (resulting in starbursts that contribute to the loss of their celestial medium and the expansion of their central bulge). Discover more about dwarf galaxies in the corresponding article, which can be found under dwarf galaxies.
4. Irregular galaxies
An irregular galaxy is a galaxy that lacks a defined shape. These galaxies are neither spiral, lenticular, nor elliptical . Some irregular galaxies are small spiral galaxies distorted by the gravity of an extremely strong neighbor.
So take note of the types of galaxies that exist in our wonderful and vast Milky Way galaxy.
