What is a Variable Star and Its Types

Introduction 

Our solar system has billions of galaxies. We live in a galaxy called the Milky Way. The whole universe has so many stars. A variable star is a concept associated with stars. A variable star is a star whose brightness is not constant. Let’s study the variable stars in depth.

What is a Variable star?

A star whose brightness is not constant is called a variable star. It simply means that the brightness of a variable star changes from time to time. The discovery of the variable star was made by David Fabricius in 1596. This discovery was possible after a very long observation of the stars for a long time. The first discovered variable star was named Mira.

Types of Variable Stars

There are two types of variable stars:

1. Intrinsic variable stars

An intrinsic variable star is a variable star whose intensity changes due to eruption due to shrinking or swelling or maybe due to pulsations.

The intrinsic variable stars have further classifications. It is further classified into pulsating variables, eruptive variables, and explosive variables. The explosive variables are also known as cataclysmic variables.

Types of intrinsic variable stars:

1. Pulsating variables

Its formation is mainly due to the change in the size of the star periodically. The periodic expansion or contraction of the star’s Stellar radius can occur for multiple reasons. This leads to the change in brightness of the star with a change in size. It is termed a pulsating variable star.

Some examples:

• RR Lyrae
• Cepheids
• Betelgeuse
• Orionis
• Antares

1. Eruptive variables

The stars in the solar system sometimes undergo violent processes. The eruptions on the surface of stars due to flares or maybe due to mass ejections can be the reason for the variable intensity of light or brightness on the star. These eruptions can cause a change in brightness which is visible. Hence, the stars whose brightness changes because of violent processes like eruption are called eruptive variable stars.

Some examples:

• Supernovas
• Novae
• Flare stars

1. Explosive variables or Cataclysmic variables

A star is a huge mass of hot gases. Thermonuclear processes may undergo on the surface of the star or maybe deep inside the star. Due to many processes, the brightness of a star may vary. These kinds of stars are hence called explosive variable stars and called cataclysmic variable stars.

Some examples:

• Dwarf novae
• Supernovas
• Novae
• Recurrent novae

2. Extrinsic variable stars

An extrinsic variable star is a type of available star whose intensity changes because of an eclipse that it faces by the rotation of any other star or planet in the solar system.

The extrinsic variable stars also have further classifications. These are further classified into rotating stars as well as Eclipsing binaries.

Types of extrinsic variable stars:

1. Rotating Stars

The stars that are present in the solar system undergo differential rotational motion. Because of this rotational motion, they may have patches on their surface. Just rotation exposes dark and light spots on the surface of the star. These dark and light spots on the surface of the stars are called patches or star spots. This may be the reason for the variable intensity of light of brightness on the stars. And These types of stars are called rotating variable stars.

Some examples:

• Ellipsoidal variable stars
• Pulsars
• Optically variable pulsars
• Alpha 2 variable stars
• SX Arietis variable stars

1. Eclipsing Binaries

We know that all the bodies in the solar system are constantly moving from one place to another. Not even a single body in the solar system is constantly present in one location. Due to this variable nature of the different bodies, it is obvious that at some other time, these bodies can come in the path of each other, or it is also possible that this body can form an eclipse. All of us are well aware of solar eclipses and lunar eclipses. We know that when the moon comes between the sun and the earth, then the light of the sun does not reach the earth.

Sun is also a star, and this is a kind of eclipse that we all are aware of and every one of us has witnessed. The same phenomenon goes with Eclipse in binaries. When a binary star in the solar system forms an eclipse with the star such that the star’s brightness does not reach us in a constant mode, then what we get is eclipsing binaries.

And these types of stars are called eclipsing variable binaries.

Some examples:

• Algol
• The brighter B-8

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