A Galaxy is a massive system of stars, planets, interstellar dust and other celestial objects bound together by gravitational force. The word galaxy is derived from the Greek word Galaxias which means milky.
There are different types of galaxies depending on its shape :
- Elliptical Galaxy
- Spiral Galaxy
- Irregular Galaxy
A general galaxy has aprox. 10^10 stars. Every star has its solar system. Our solar system is one of them. Beside stars , planets and all other celestial bodies there are also some dark matter which is still to be discovered.Every galaxy has a Super Massive Black Hole (SMBH) as its core which is responsible for its formation. It attracts the clouds of Hydrogen and give birth to the galaxy. It is its gravitational pull which binds all the constituents of the galaxy together.
The galaxy having that type of SMBH that eats up the surrounding interstellar dusts and shoots up the jets are Active Galaxy and the one having no jets is known as Dead Galaxy. Our Milky Way is one among dead.
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