Short story : Types of Stars

Short story : Types of Stars

Types of Stars
Life cycle of a star. A star has a lot of phases
In its life cycle.

Stars are the ultimate visibility factor we have in space. Without stars  the Universe would completely shred off to darkness. Stars are huge balls of burning gases, producing light and heat for billions of years. The fuel required for this bohemoth process comes from nuclear fussion, in this process the most common element found in the Universe Hydrogen is continously converted into Helium, which in turn produces energy in the form of heat and light.

But do all the stars in the Universe are of the same type ? Not exactly, on the basis of our understandings of the Universe, Stars may be the most diverse things possible present. From tiny brown dwarfs to red and blue supergiants. There are even more bizzare stars such as neutron stars and Wolf - Rayet stars. So let's see the different types of stars.


Types of Stars
Our Star The Sun is a yellow dwarf
Star type, currently it is half way its
Life, that is 5 billion years.

To understand the perception of different types of stars we firstly need to understand our own star The Sun and its physical characteristics. 

Our Star is a type Yellow Dwarf Star with life expectancy of about 10 billion years. Mass of our star is about 1.98 × 1030 kg. Average temperature being 5,500 °C with luminosity of  3.846 × 1026 W and radius 695,500 km.

Yellow Dwarf Stars

  • The Sun, Alpha centauri - A, Kepler - 22 and 51 Pegasi fall under this type.
  •  Stars falling under this group have a life expectancy of 4 - 17 billion years. 
  • Surface temperatures of 5,300 to 6,000 k.
  • These type of stars are main sequence stars ( stars which have attained their mature age), they are at their prime peak as they are burning hydrogen at their cores.
  • These stars after burning for about 10 billion years collapse under its own gravity, to become a red Dwarf much bigger in size than it used to be.
  • These stars are mainly white in colour, yes they do appear yellow from Earth due to transitions occured by our atmosphere.

Orange Dwarf Stars

Orange Dwarf Stars are K - type main sequence stars, in the intermediate class of M - type sequence stars ( red dwarfs ) and G - type sequence stars ( stars like our sun ).

•  These stars have masses of 0.5 to 0.8 to that of our Sun.

• Surface temperature of 3,900 to 5,200 k.

• Stars like Alpha Centauri B and Epsilon Indi fall under this category.

• Life expectancy is about 15 - 30 billion years.

• These stars are the particular interests to look for extraterrestrial life because they possess stable sequence star life for very long period (like our sun has life expectancy of just 10 billion years).

• These stars emit less ultraviolet radiations than the G - type Yellow Dwarfs.

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Red Dwarf Stars

• A Red Dwarf Star is smaller and relatively cooler in the main sequence.

• Red Dwarfs have mass about 0.075 to 0.50 to that of our Sun.

• Surface temperature of less than 4,000 k.

• Red Dwarfs are the most common type of stars found in the Milky Way, according to estimates 3/4 th of all the stars in the Milky Way are Red Dwarf stars.

• Due to low luminosity, these type of Stars are not easily observable.

Thermonuclear fusion in these type of stars are in prolonged state because helium produced during fusion is not accumulated at the core of the star due to convection.

• An example of this star is Proxima Centauri.

Blue Giant Stars

Types of Stars
In astronomy, blue colour indicates
Hot. Hence, the blue giant stars are
Very hot and luminous as well.

Blue Giants are hot stars with a luminosity of class III.

• These stars have radius of 5 - 10 times to that of our Sun.

• Temperatures of about 10,000 k and upwards.

• These Stars are not Blue giants all their lives rather they are a stage in the stars life.

• These stars can have the luminosity of about 100,000 times to that of our Sun.

Plaskett's star is an great example of such class.

• These stars are formed when the core Hydrogen is exhausted.

• These are massive stars with short life.

Red Giant Stars

Types of Stars
A red giant star burn out all the
Hydrogen in its core but hydrogen
Fusion still takes place inside shells
Around the core.

Red Giant Stars are huge luminous stars with low or intermediate mass, 0.3 to 0.8 solar mass.

• These stars have exhausted the supply of hydrogen in their cores and have started thermonuclear fusion of hydrogen in shells around the core.

• They remain inflated or swollen, hence their radii's are tens to hundreds times to that of our Sun.

• Despite of their lower density, Red Giant Stars are more luminous than our Sun because of their greater size.

• Surface temperatures about 3,000 to 4,000 kelvin.

Gamma Crusis, 88 light years away and Arcturus 36 light years away are best known examples of Red Giant Stars.

Red Supergiant Stars

Types of Stars
Betelguese : A Red Supergiant Star

Red Super Giants are cooler and larger.

• Temperatures below 4,100 K.

• They are about hundred to thousands times the radius of the Sun.

• These stars exhaust the hydrogen in their core, hence no hydrogen fusion is possible rather Red Super Giants fuse helium to produce Carbon and Oxygen.

• Although Red Super Giants are much cooler than the Sun but due to their greater size they are much more luminous as well.

• These stars have masses of about 10 million to 40 million Sun's.

• The lack of proper surface gravity and higher luminosity results in extreme mass loss, millions of times higher than that of the Sun, producing observable nubalae around the Star.

• More the size of the star more is the loss of mass. The mass of the stars reach about 10 million Suns by the time their cores collapse.

• Red Super Giants are observed to rotate slowly or very slowly.

Betelguese and Antares are the brightest and well known Red Super Giant Stars.

White Dwarfs

Types of Stars
White Dwarf : Sirius B

White Dwarfs are stellar core remnants composed mostly of electron degenerate matter.

• White dwarfs are very dense, its mass is comparable to that of Sun and its volume to that of the Earth.

• Its luminosity is due to the stored thermal energy.

• No fusion takes place in these stars.

• White dwarfs are thought to be last evolutionary stage of stars whose mass is not high enough to become a neutron star.

• A white dwarf is very hot when formed but due to no access of source for energy, it gradually radiates it energy to cool.

Sirius B and Procyon B are examples of White Dwarfs.

Black Dwarfs

A black dwarf is a stellar remnant, basically a white dwarf that has cooled down to such an extent that it now has no energy to emit heat or light.

• The time required for a black dwarf is estimated to be more than that of the age of Universe (13.8 billion years), hence it is believed that no black dwarfs exist.

• Black dwarfs would have a mass less than 0.8 the mass of the Sun.

• Due to a very low mass black dwarfs are not capable of hydrogen fusion.

Neutron Stars

Types of Stars
Neutron Stars are very small
And very dense.

Neutron Stars are the collapsed core of a giant star which during its life had about 10 to 29 solar masses.

• They are the smallest and densest.

• Radius of about 10 kms and mass between 1.4 to 2.16 solar mass.

• They are almost completely composed of neutrons (subatomic particles with no net charge).

• Neutron stars are very hot with surface temperatures about 600,000 K.

• Their magnetic fields are about 100 million to 1 quadrillion times to that of the Earth.

• Some stars emit beams of electromagnetic radiations and are known as Pulsars.

• There are thought to be about 100 million neutron stars in the Milky Way alone.

PSR J0108-1431 and LGM-1 are two common known neutron stars.

According to you what is the Sun's fate ? Let us know in the comments section !


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