As galaxies are one of the most fascinating structures in the whole universe. They are gigantic conglomerates of celestial bodies gravitationally bound. But how are they formed? This is a question that still intrigues astrophysicists around the world.
Estimates indicate that there are at least 200 billion of them in the universe. But there are those who think that this number is modest, and there may be up to 10 times more. We don’t know the exact amount, but we already know millions of them.
The galaxy we live in is called the Milky Way (Source: Wikimedia Commons/Pablo Carlos Budassi)Source: Wikimedia
This is because they are relatively easy to observe. The amount of energy these systems emit is so great that it reaches us even over the greatest distances. One of them is the object astronomical farther than we know. It’s called GN-z11 and it’s 32 billion light-years away.
When you look up at the night sky, you might be seeing a lot of them. It’s just that seen from here, they can look like a single bright dot and we mistake them for stars. But looking better, with a telescope, for example, it is possible to see beyond appearances.
The origin of galaxies may be linked to the universe itself. After the Big Bang, space was composed only of hydrogen and helium atoms. Observations made by Hubble point out that in just 1 billion years later there were already conglomerates of celestial bodies.
How did galaxies arise?
There are two main theories about their formation. According to the first, the galaxies were born after primitive stars emerged from the two original chemical elements and collapsed under their own gravitational pull.
The second, which is gaining a lot of attention lately, states that the universe young already had small “clumps” of agglomerated matter that, with time, gained mass and evolved to form galaxies.
Galaxies are some of the oldest objects in the universe (Source: Wikimedia Commons/ESO)Source: Wikimedia
THE Hubble Telescope was able to photograph these supposedly smaller sets of space objects, lending strength to the theory.
Until the beginning of the 20th century, it was thought that everything in the universe was it was within our own galaxy. But some astronomers have hypothesized that there could be more beyond here.
They pointed to spiraling bubbles in the sky and called them universes. islanders. Until then they were believed to be formed of dust and gas, but in 1924 Edwin Hubble identified clusters of pulsars that were beyond the distance that the Milky Way reached.
What types of galaxies?
Today, we already know millions of them, and we can categorize them according to their characteristics. In general, the shape of one says a lot about it, so that’s the first factor we take into account. There are two main groups.
As galaxies elliptical, as the name implies, has an ellipsoidal shape, without spiral arms. Therefore, they have a more homogeneous distribution in the three directions of space, without a rigidly organized structure.
The galaxy NGC 1316 is of the elliptical type (Source: Wikimedia Commons/NASA)Source: Wikimedia
Their format varies. Some are nearly spherical and others are very elongated. They tend to have less gas and dust, and older stars, which in turn may have more random orbits.
Some astronomers believe that ellipticals are actually formed from the collision of two (or more) galaxies spirals. This second type is the one with arms, like ours, that circle around its center.
It represents most of the galaxies known to us. Their shape is caused by a translational motion of all the gas and dust they contain at speeds of hundreds of kilometers per second, around their center.
The barred spiral galaxy NGC 1300 (Source: Wikimedia Commons/NASA)Source: Wikimedia
They all have two arms, which can be more or less tight around the core. Some are also barred, that is, they have a linear band of stars at their center. This is our case.
Generally, the closer to the center, the older the stars. In the arms is where the star formation regions are concentrated.
The core of these galaxies it is formed by very old stars and very close to each other. In addition, they often have one or more black holes that can be very large and massive in some cases.
An irregular, ring-shaped galaxy called the Hoag Object (Source: Wikimedia Commons/NASA)Source: Wikimedia
Even more impressive are those that have a quasar at their center. These objects are the result of a supermassive black hole, capable of releasing immense amounts of energy — the largest in the entire universe.
The rest of the galaxies, that is, those that are not elliptical or spiral, are grouped under the heading of irregular or peculiar. They occur in the most varied formats and structures, and are very interesting.
One of them is the galaxy ring, which consists of a group of stars that surround an empty core. It is believed that they are formed by the passage of a dwarf galaxy by the core of a larger spiral that destabilizes it.
The Large and Small Magellanic Clouds, which can be seen with the naked eye, are galaxies (Source: Wikimedia Commons/ESO)Source: Wikimedia
Another curious type is that of galaxies lenticulares. They are in the middle ground between elliptical and spiral: they are formed by very elongated disks, but they do not form arms. In general they have few young stars.
There are also dwarfs and satellites. That is, smaller groupings, or that accompany galaxys bigger. The Milky Way alone has more than 50 of them. Two are visible at night and have been known since antiquity. They are the Small and Large Magellanic Clouds.
Galaxies are fascinating stellar objects that have enchanted human beings since the dawn of time. In the last century we have advanced a lot in studies and learned more about them, and yet there is still much to discover in our sky.