A galaxy is a vast collection of stars, gas, dust, plasma, and (possibly) unseen dark matter bound together by gravity. Though each galaxy has its own unique shape, the three main shapes are Elliptical, Spiral and Irregular. Our galaxy, the Milky Way, is a spiral galaxy. Some galaxies are found alone scattered about the universe. However most galaxies are found huddled in clusters. There are also clusters of clusters of galaxies known as superclusters.
History
At one second the universe was an atom. Microseconds later it became what it is today. In the first few minutes of the Universe, when the temperature was above a trillion trillion degrees celsius, chemical reactions within atoms caused the first elements to be formed, hydrogen and helium. These elements were soon found in large chunks known as stars. Due to gravity stars started to be found in clusters known as galaxies.
Galaxies started to move away from each other in the ever expanding universe. Galaxies are fighting between the battle of forces in which gravity is trying to collide galaxies and the universe is trying to spread out galaxies.
Discovery
In ancient times, people thought that the Earth was in the center of the Universe and all other bodies revolve around it. Only objects in the solar system that could be seen by naked eye were believed to exist.
Copernicus, who opposed this model, proposed his own model in which the Sun was in the center of the solar system and its gravitation held planets in its orbit.
With the invention of the telescope, various astronomers discovered various celestial bodies outside the solar system.
Before Edwin Hubble, astronomers assumed that the Milky Way was the entire universe. Hubble proposed that there are many galaxies. Charles Messier produced a catalogue in which he wrote his observation. However little did he know that many of his observations were actually galaxies. Such as M31 was later found to be the galaxy Andromeda.
Scientists today have identified thousands of galaxies across the Local Supercluster and beyond.
Future
There is a long debate between cosmologists about the future of galaxies and the universe. Many think that at one point gravity will merge galaxies together and bring the universe into what it was earlier: The size of an atom. However, many also think that gravity will never be able to stop the Universe form expanding and the Universe will last for ever.
Gallery
References
- DK Encyclopedia of Space.
- Starmatt.com