Everyone knows about our solar system and the planets around it. Our galaxy, the Milky Way, is a bunch of thousands of solar systems, each with a dozen planets. That could mean millions of planets in our galaxy, but in the universe, there could be millions, if not billions of galaxies, each with millions of planets. The chances that there is only one planet with life on it (Earth) is astronomical. Today, we shall see the features of galaxies.
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Our Milky Way galaxy is about 12- 10 billion years old. Galaxies are made when immense clouds of gas collapse in on itself and start to rotate. They have nebulas, and due to nebulas stars are formed. I have explained in detail how stars are formed in ‘A Guide to Stars’, my earlier post. Almost all galaxies have a supermassive black hole in the center of the galaxy, around which all the stars and solar systems rotate around. This happens not because of the gravity of the black hole, but because of dark matter. I have explained dark matter in another post as well.
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           When the Milky Way was created, the universe was still young, and all things were ramming into each other. Now, the universe has settled down, and we have a spot in the most remote area of the galaxy. The supermassive black hole in the center of the Milky Way, is quiet, but other galaxies’ black holes can devour thousands of solar masses. We cannot see the black hole in the center of the galaxy, but we know it’s there, as the stars orbit a seemingly empty spot, and some stars too close just disappear.
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           The largest Galaxy in the universe is IC 1101. Galaxies also have groups called clusters. The Milky Way is in a group with the Andromeda galaxy and some other galaxies. This group is in a cluster, made of different groups. The Milky Way is in the Laniakea supercluster, which is the largest single thing in the universe.
Sources used-
·     Wikipedia
·     Space.com