Disk galaxies or spiral galaxies are a type of galaxies which were first discovered by the American astronomer Edwin Hubble. Spiral galaxies are flat and disk-shaped. They contain stars, dust, asteroids and gas and serve as a residence to a group of stars located in the center of the galaxy. This center is known as the bulge.
Spiral galaxy is the most common type of galaxy, as almost 60% of observed galaxies in the universe are spiral galaxies. There is no surprise here that spiral galaxies look like spirals, but if you are able to get a distant clear view from the side then galaxy would look like a vast circle. A clear view of this galaxy is called the "Face on Spiral", and from the side it is called "Edge on Spiral". Spiral galaxies usually have arms (cluster of stars) that are joined very closely to them, while other galaxies are not so much close to their exterior clusters of stars.
Spiral Galaxy Formation
No one really knows how various galaxies were formed and how was the universe created. But we do have some rough information about the origin of spiral galaxies.
In early 20th century astronomy, Edwin Hubble formed an idea about the expansion of universe. People have estimated the approximate age of the universe based on its rate of expansion. Some existing galaxies are a billion light years away from us, which means that they are the oldest. In 1962, astronomers Olin Eggen, Donald Lynden-Bell and Alln Sandage suggested that spiral galaxies form due to the collapsing of large gas clouds. When the cloud falls it settles and the erupting gas takes a form of a rotating disk. This theory was very popular at some point, but is no longer accepted.
Spiral galaxies are quite fragile and thin so they merge with other galaxies very easily, this merger makes it more difficult to understand their formation. As spiral galaxies continue their joining streak they gather more and more mass which makes them thin. This thinness causes the expansion of gas in the galaxy to contract thus making it extremely thinner. Astronomers still don't have a definite answer on the formation and merger of galaxies, however, in recent years a great amount of research has been done to understand this concept. Galaxies travel the universe and collide with each other, sometimes this collision destroys them and sometimes they merge and become a bigger galaxy.
Now that the concept of a spiral galaxy is clear, let's have a look at some of its facts which would help to simplify this concept a little more.
- In 2005, it was confirmed that our own galaxy, the Milky Way is an example of a barred spiral galaxy.
- According to many leading space research websites, out of over three quarters of galaxies discovered, 80% of them are spiral galaxies.
- NASA claims that all spiral galaxies rotate and some of them take help of eons to complete one single rotation. The organization has also named almost every galaxy known to man.
- How close are the arms of spiral galaxies actually help astronomers classify the additional group of stars around them.
- Some researchers believe that the spinning motion of galaxies which is at hundreds of kilometers per second is responsible for the distinctive spiral shape of the galaxy.
- Within a spiral galaxy, millions of new stars are born after a specific period and scientists believe that their disks are made of halo, which is supposed to be rich source of dark matter. With the birth of these new stars large amounts of gases and dust are also formed.
- Small clusters that are formed outside the spiral galaxy have more than a million stars in them which constantly encircle these galaxies.
There are many more amazing facts about the universe that are yet to be discovered. If you find any more interesting information about spiral galaxies, please leave your valuable comments in the suggestion box.