The galaxies: Everything you need to know about

Introduction

Almost everyone is familiar with the word Galaxy. But people know very little about them. So here in this article, we are going to discuss galaxies. Our solar system is a part of the galaxy which is known as the Milky way galaxy. The galaxy is simply a huge collection of stars and they are very very vast in size. Galaxies usually contain stars, white dwarfs, neutron stars, black holes, interstellar gases, dust, and dark matter. So you can see how many things the galaxy contains but still most of its space is empty. Most galaxies are organized in a group which is called a cluster or supercluster. The reason behind this organization is the force of gravity that holds them together. The Milky Way galaxy is a part of a local group that is again a part of a supercluster which is known as the Virgo supercluster.

Most of the galaxy contains black holes. These black holes produce a tremendous amount of energy. And they can be seen easily by astronomers from the farthest distances. These black holes may be active and very big. While some of the galaxies contain quasars. Quasars are the most energetic and shiny objects in the universe. Quasars are billions of times bigger than our sun.

Formation of galaxies

No one knows exactly about the formations of the galaxies. As we already know, after the big bang the universe contains only two main particles, helium, and hydrogen. Some astronomers think that the formation of stars from gas and dust takes place first. And then they all group into a galaxy by the force of gravity. While some astronomers think that the cloud is organized together by gravity before the formation of the stars. And after this organization, the formation of stars takes place within the space of the Galaxy.

Historical background

If we look into history, at the beginning of the 20th-century astronomers thought that the whole universe was within our Milky Way galaxy. Or we can say our galaxy is the only universe. And nothing is there beyond our galaxy. But later on, the researcher concludes that there are also some stars or we can say galaxies are there which are very far away from our Milky way galaxy. Then we come to know that our galaxy is not only one, it is only a small part of the universe. And the universe includes millions and trillions of galaxies.

Later Hubble, while measuring the distance of other galaxies from us, discovered that the galaxies are moving away from us at a tremendous speed. And he also discovered that the more the distance of the galaxy from our galaxy the more accelerating speed it is moving away from us. This discovery leads to the conclusion that the universe is expanding at an accelerating speed.

Shape of the galaxies

Astronomers classified galaxies based on their shapes. These shapes are particularly of three to four types. Shapes of galaxies are classified based on their appearance. And named also based on their appearance from our earth. Also based on their shapes they have different properties and characteristics. And also just by seeing their shape, we can make productions about its history of evolution. So let’s discuss different types of shapes of galaxies.

Spiral

In this particular type of shape, there is a central hub of the stars which is surrounded by spiral arms. Our Milky way galaxy comes in this category. And also interestingly the gas and dust in this type of shape revolve around the center at a tremendous speed of hundred miles per second. And due to the presence of gas and dust in the galaxy the formation of new stars is a constant process.

How spiral arms form

As in the solar system, the planets revolve around the sun in the galaxy the star orbits the center of the galaxy. Spiral arms appear where the star passes in and out through the crowded areas. One theory says that these happened because the stars don’t have neat and parallel orbits.

Elliptical

In this type of shape, there are no spiral arms present in the galaxy. Also, their shapes range from very stretched out to circular. They also lack the amount of dust so the formation of new stars does not take place. This shape-type galaxy usually contains older stars. Also, astronomers think that more than half of galaxies are elliptical.

Irregular

This type of shape is rare in the universe. They are neither spiral nor elliptical. They lack the perfect shape or appearance of a distorted one. This type of shape is Highly affected by the gravity and influence of the neighboring galaxies.

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Collision of galaxies

Galaxies don’t flow freely in space as they are part of clusters(a group of galaxies). Some of the clusters are large and contain many galaxies while some are small. Our Milky Way galaxy is part of the cluster known as the local group. And the local group contains 50 galaxies. Galaxies collide and merge their stars and dust. This is one of the important steps in their growth and evolution. In the collision of the galaxies, the individual stars do not collide with each other but the gas clouds do. But due to the influx of gas and dust the rate of formation of stars increases. Galaxies merge into a new shape after the collision.

There are some predictions that our Milky Way galaxy is going to collide with the Andromeda galaxy. The Andromeda galaxy is the nearest neighbor of our galaxy. During the collision, the galaxies are rushing toward each other at any speed of 112 km per second.

Text credit: European Space Agency (ESA)
Image credit: ESA/Hubble & NASA, A. Adamo et al.

Last Updated: Oct 30, 2020

Some important information 

The galactic center is the center of the galaxy. It contains the stars and gas cloud packing. And a black hole is usually found in this area of the galaxy. Our Solar system is located in a minor spiral arm called Orion’s arm. Solar system orbits around the center of the Milky way galaxy. It took 200 million years for our solar system to complete one cycle of orbit. Our solar system orbits the center of the Milky Way at a speed of 200 km per second. We know that the cloud of gas and dust can be found everywhere in the Milky way galaxy especially in the spiral arm.

A crab nebula is the cloud of breakage left behind by a dying star that exploded. The region above and below the spiracle disc is known as the halo. And some of the stars also lie in that region. The globular cluster is tightly packed balls of an ancient star floating in the halo region.

Some important fact about galaxies

  • The average size of galaxies is 3,000 to  3,00,000 light-years ( 2.83 × 10^16 km to 2.83 × 10^18 km).
  • Galaxies that contain hundred million (10^8) stars are known as dwarfs. While galaxies that contain hundred trillion (10^14) stars are known as giants.
  • GN-z11 is the galaxy that is the oldest and at the farthest distance from us among the all known galaxies. And the distance between the Earth and GN-z11 is about 32 billion light-years.
  • In 2021, the discovery by NASA’s new horizon space probe discloses that the actual number of galaxies in the observable universe is 2×10^11 and the number of stars is 1×10^24.
  • The number of stars in the Milky Way galaxy is near about 200 billion.
  • Our solar system has orbited the Milky Way galaxy 23 times.
  • 6000 years is the time it would take you to count the Milky Way’s Stars at the rate of one a second.

Conclusion

Not only the universe but also our Milky Way galaxy is full of mysteries and beyond imagination. No one knows everything about the galaxies. The new theories, observations, and facts get updated almost every year. Many mysteries were solved by discoveries and many are remaining. I hope after reading this article you get much knowledge about the word Galaxy. We discussed the formation, history, and the different shapes of the galaxies. Some interesting facts are also discussed here. We also mentioned the collision of galaxies in this article. But many things are still under investigation, many types of research are kept going on the things which we are not familiar with. I hope you enjoyed the article.

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