Galaxies are vast groups of stars held together by a pulling force called gravity. Inside a galaxy the region in between stars called interstellar, can be empty or full with gaseous dust clouds like nebula, rocks planets, ice elements, etc.
Found Something Interesting? This is our galaxy, we call it MILKY WAY.
People used to think that our own galaxy, the Milky Way, was the whole universe. So, the universe is often called ‘the Galaxy’.
Later, the famous astronomer Edwin Hubble proved that swirly star clouds called spiral nebulae (later named as Spiral galaxies) were not inside our galaxy, they are separated and very far away from ours. He also showed that the farest galaxies are moving farther with time.
Suddenly, we had found the universe is a lot bigger. And, it is expending.
With increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary—the utmost limits of our telescopes.
Types of Galaxies
Even though there are many type of classifications for galaxies but most popular classification is based on by their shapes and they are three types.
Spiral and barred spiral galaxy
A barred spiral (SB) galaxy is a spiral galaxy (S) with a central bar-shaped structure composed of stars.
Irregular galaxy (Irr) doesn’t fit into spiral and elliptical type of galaxies. Some of deformed spiral or elliptical became irregular galaxy also.
Elliptical and Lenticular Galaxy
A lenticular galaxy ( S0) is a type of galaxy intermediate between an elliptical (E) and a spiral galaxy (S).
A diagram called "Hubble Tuning Fork Diagram" can show the galactic classification.
Other Well-known Types of Galaxies
NGC 5477, small size
NGC-5128,Active Galactic Nucleus (AGN)
The Antennae Galaxies, peculiar interacting galaxies
NGC 7742, bright core