Galactic Collisions

 

      

       

        In the previous blog "Galaxies" we saw about the types of galaxies, active galaxies and that the Andromeda galaxy will collide with the Milky Way galaxy.

The collision is inevitable but won't happen now as it may take several billion years. When the collision occurs both galaxies may pass each other the first time, but in the next few hundred million years it will bounce back and collide that may form one bigger galaxy probably an elliptical galaxies which astronomers call the "Milkomeda". During the collision the sun may go farther into the galactic suburbs or further into the galaxy. It may still orbit around the new center of Milkomeda and earth may still exist, that is if it survives for a few billion years.

Fact: It is believed that elliptical galaxies are formed due to Galactic Collisions.

It is less likely that two stars will collide when the galaxies merge, as they a have a lot of space between them. The two super massive black holes may eventually go into orbit around one another and any gas and dust left out by star formation during the collision will be gobbled up by the black holes. During this event the galaxy may turn into an active one. All galaxies doesn't form Elliptical galaxies on collision. If there is a big spiral galaxy and a smaller one collides it just gets absorbed by the big spiral galaxies. It's believed that most of the large galaxies are formed by devouring smaller galaxies.

Our own galaxy is in the process of devouring such smaller galaxies.

Now comes the peculiar galaxies. These are also formed due to collision. These galaxies form all kinds of distorted shape.

Sometimes a small galaxy plunges right through the heart of a bigger one. The gravity of the small galaxy draws in stars from the bigger one and flings them away. In simple words, like ripples in a pond. This results in the formation of ring like galaxy. The famous Cartwheel galaxy is a good example of this.

There are also irregular galaxies. Their shape is so distorted that they they lost their original structure due to collisions.

Now things are gonna get pretty large.

When we venture out of the local group, there are many similar clusters of galaxies. The closest one to the local group is the "Virgo super cluster" in the direction of the star Virgo. It is about 15 million light years away and contains thousands of galaxies. Galaxies in a galaxy cluster are bound to each other because of their mutual gravity. There are many such clusters of galaxy. But this is not the end. Several dozen clusters clump together to form a super cluster that are hundreds of millions of light years across. The local group and the Virgo super cluster is located in the "Laniakea Supercluster" that spreads across 500 million light years. There are many such Superclusters in the universe. They form a network and has a lot of space between them or void.

And Finally a question arose. How many galaxies are there in the Universe, can we count them all? 

To know the answer they aimed the Hubble space telescope at the most empty part of the night sky. They let it collect light for a long period of time to detect faint objects and the results they got was mind-boggling.

There was thousands of galaxies in a tiny segment of the empty night sky. This is the Hubble deep field. This tiny portion of the sky was the size of a grain of sand.

This experiment was performed in different sections of the sky and the same results were found. This give us an idea about the size of the universe and the number of galaxies. So the Universe has billions of galaxies, with each galaxy having billions of stars.