What are the different shapes of galaxies?

In the vast space around us, there are numerous galaxies present, which are known as large groups filled with stars, dust, and gases all held together due to gravity. All the galaxies are likely to contain stars, planets, moons, comets, asteroids, black holes, nebulae, dust, neutron stars etc. 

Just like our solar system that lies in the Milky Way galaxy, there are many galaxies in the space. Every galaxy moves at certain speed and exists in a certain shape. Our milky way galaxy is in the spiral shape with a bright bulge at its center.

The famous astronomer Edwin Hubble studied the galaxies for many years and found that there are four shapes in which the galaxies expand. This classification system is known as Hubble sequence and the four types are

• Spiral
• Lenticular or Barred spiral
• Elliptical
• Irregular

Spiral Galaxy:

Spiral galaxy is the Galaxy that was formed in a spiral shape with a distinct flattened disk-like structure with a bright center called a nucleus. Our Milky Way galaxy is an example of the spiral galaxy. The young stars are formed in the outer arms of the galaxy while the old stars are formed in the inner arms. There are four subgroups of spiral galaxies, such as

• S0- have bright nucleus but no spiral arms
• Sa -have spiral arms that wound tightly around the nucleus
• Sb – have spiral arms that tend to extend like barred spiral ones
• Sc – galaxies are wound much more loosely

Barred Spiral Galaxy: 

The Barred spiral galaxies which are one-third of the universe are the ones that have their arms spiral out from a straight bar of stars instead of coming from a nucleus. The barred spiral galaxies are represented by the letters SB are divided into barred subgroups as SBA, SBb and SBc which differ from having a short bar of stars to long and well-defined bar of stars extending out.

Elliptical Galaxy:

The Elliptical galaxies vary in shape from round to extremely elongated oval but have no bright nucleus. These galaxies are represented by the alphabet E and are divided into seven sub-groups from E0 to E7 which range from nearly circular to extremely elongated ones.

Irregular Galaxy:

As the name implies, these galaxies have no discernible shape or structure. These are divided into two classes such as Im and I0. Im class galaxies show some kind of structure which are faint remnants of spiral ones, whereas I0 class galaxies are chaotic in shape.

A galaxy can be defined as a gravitationally bound system comprise of stars, interstellar gas, stellar remnants, dark matter, and dust. There are three types of galaxies which are elliptical, spiral and irregular, based on their visual morphology.

Elliptical Galaxies:

The shape of Elliptical galaxies is like an elongated sphere or a spheroid. Only two out of its three dimensions are visible in the sky. As you go farther from the center the light tends to get smoother with the decreasing surface brightness. 

Elliptical galaxies have been provided a classification that corresponds with their elongation which is from a perfect circle also known as ellipticity. Its ellipticity is directly depending on the number. If the number is large the galaxy becomes more elliptical. Elliptical galaxies have no specific axis of rotation.

Spiral Galaxies:

There are three main components of spiral galaxies which are a bulge, disk, and halo. The bulge is found at the center point of the galaxy and it has a spherical structure. It mainly contains the older stars. 

The disk comprises of gas, dust and younger stars and form arm structures. The halo is a spherical structure which is located near the budge and also around the disk. Spiral galaxies are further classified into two groups which are ordinary and barred.

Irregular Galaxies:

Irregular galaxies do not have any symmetrical or regular structure. They are classified into two groups which are Irr 1 and Irr 2. The galaxies which are Irr 1 type have regions which have elemental hydrogen gas and Population 1 stars which are hot young stars. 

Irr 2 type galaxies have a portion of dust which blocks the light coming from the stars. The visibility of distinct stars is almost nil due to this dust in the galaxy. 

These are the types of galaxies and their shapes which are found in the space.

Galaxy is coming from Greek word “galaxi” and is a vast collection of billions of stars, dust and hydrogen gas, isolated in space from similar systems. Galaxies are the building blocks of the universe. There are about 100 billion galaxies in the universe, and each galaxy has on an average 100 billion stars. The two important galaxies in the universe are:     

• Milky way galaxy
• Andromeda galaxy

Milky Way galaxy comprises of billions of stars, hydrogen gas and dust. It is 100,000 light years in diameter. The solar system is a part of the Milky Way galaxy. The galaxies were formed by the shrinking of vast over dense clouds of hydrogen gas and dust.

Classification of galaxies:

Galaxies have many different shapes and size. The galaxies are usually classified on the basis of their shape. Three types of galaxies are discussed below:

• Spiral galaxies: They are the most familiar type in the universe. Our Milky Way is an example of a spiral galaxy. Spirals are large rotating disks of stars and nebulae which are bounded by a shell of dark matter.      

• Elliptical galaxies: Elliptical galaxies are almost egg-shaped which is present in galaxy clusters and smaller compact groups. Elliptical may have hundred million to hundred trillion stars, and they can range in size from a few thousand light-years across to more than a few hundred thousand. 
• Irregular galaxies: Irregular galaxies are irregular in shape. Small Magellanic Cloud is an example of the irregular galaxy. Irregulars generally do not have sufficient structure to describe them as spirals or ellipticals. They may have the active area of star arrangement, and a number of smaller ones are listed as “dwarf irregulars”.                    

According to the scientific findings, universe is composed of billions of galaxies and among them one is Milky Way. One single galaxy is composed of huge number of stars so big our whole universe is. Though much study is still in progress regarding various galaxies and their characteristics, one thing which we discovered earlier was their shape. Edwin Hubble, an astronomer, provided us with the information that galaxy can possess either of these four shapes, spiral, elliptical, lenticular and irregular.

Spiral Shape:

Spiral shape is most common shape of galaxy in Universe. Milky Way itself is spiral in shape. A spiral galaxy looks like a pin wheel and is basically the nucleus with arms spiraling outwards to inwards. It can be tight or loose or young or old, based on age of stars. Most commonly, young stars are located in the outer arms whereas older stars are located near the center.

Elliptical and Lenticular Shapes:

Elliptical and lenticular shaped galaxies are very similar to each other. Their prime features are they have very few dust lanes and are mainly composed of older mature stars. These shapes have star forming regions. Compared to other shapes, these shapes are more cohesive and organized.

Irrregular Shape:

Last galaxy shape is  irregular. They have an indeterminate shape. These galaxies are often small and don’t have enough gravitational force to organize into a more regular form. Many images of irregular galaxies have been taken fro Hubble telescope like the Magellanic Clouds. Irregular galaxies can also be large galaxies that have undergone a major gravitational disturbance.