Classification of Galaxy

Classification of Galaxy 

Classification of Galaxy


What is Galaxy?

A galaxy is a large collection of stars, gas, dust, and other celestial objects held together by gravity. Galaxies come in a variety of shapes and sizes, ranging from small irregularly shaped galaxies with just a few hundred million stars to massive spiral and elliptical galaxies with trillions of stars. The stars within a galaxy are organized into various structures, such as spiral arms, bulges, and halos. Galaxies also contain supermassive black holes at their centers, as well as clouds of gas and dust that form new stars. The study of galaxies and their properties is an important area of research in astronomy and astrophysics, providing insight into the formation and evolution of the universe.

Classification of Galaxy 

Galaxies are classified based on their morphology or structure. The most common classification system was developed by Edwin Hubble in 1926, known as the Hubble sequence, which divides galaxies into three main categories: Thes are given below ⬇️

  1. Elliptical, 
  2. Spiral, and 
  3. Irregular.

Elliptical

Elliptical galaxies are shaped like ellipsoids or spheres and have a smooth and featureless appearance. They are classified according to their degree of flattening or elongation, ranging from E0 (perfectly spherical) to E7 (highly elongated).


Spiral

Spiral galaxies are characterized by a central bulge and arms that spiral outwards. They are further subdivided into two types: barred and unbarred, depending on whether a straight bar of stars runs through the center of the galaxy or not. The arms of spiral galaxies can be tightly wound (classified as Sa), moderately wound (Sb), or loosely wound (Sc).


Irregular

Irregular galaxies do not have a well-defined shape or structure and are classified as such due to their chaotic appearance. They can be further subdivided into two types: Irr I and Irr II, with Irr I being more asymmetrical than Irr II.


In addition to the Hubble sequence, there are other classification systems that take into account other properties of galaxies such as their color, size, and luminosity. However, the Hubble sequence remains the most widely used and recognized system for classifying galaxies.


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