What are Stars?

Stars are the heavenly bodies like the Sun that are extremely hot and have light of their own.Stars are made up of Hydrogen gas, some helium and dust. In all stars (including the sun), hydrogen atoms are continuously being converted into helium atoms and a large amount of nuclear energy in the form of heat and light are released during this process. All stars are very big in size. the stars twinkle at night ,i.e. the intensity of their light appears to increase and decrease continuously.

Birth, Evolution & Death of a Star

Like human beings stars also take birth and after completing their growth stages they finally die. So, lets have a look at the different stages of star’s birth , evolution and Death of a star.

Intro: The raw material for the formation of a star is mainly hydrogen gas and some Helium gas. The life cycle of a star begins with gathering of Hydrogen and helium gas present on galaxies to form dense clouds of these gases.

1) First Stage- Formation of a Protostar

Protostar is a highly condensed cloud of gases, mainly Hydrogen and some Helium, formed by the gravitational contraction of gases present in the galaxy. A protostar looks like a huge, dark, ball of gas.This protostar does not emit light. it is only a stage in the formation of a complete star.

2) Second Stage- Formation of Star from Protostar

In this stage we will get to know how a complete star is formed.

The protostar formed above is highly dense gaseous mass which continues to contract further due to high gravitational force. Due to contraction, the hydrogen atoms presents in the gas cloud collide with one another more frequently thus raises the temperature of protostar more and more for about millions of years( temperature increases from -173 degree Celsius in the beginning to about 10*7 times degree Celsius).So as a result, nuclear fusion reaction of hydrogen start taking place, resulting in formation of the core of Star.

4 H1                      …..FUSION….>                      4 He           +              Tremendous Energy

Four hydrogen                                     One Helium

Nuclei                                                    Nucleus

Here, 4 Hydrogen Nuclei fuse to produce a bigger Helium Nucleus. Thus a star formed containing a core(in center) and an outer shell or envelope covering it.

3) Final stage

Now in this stage a star first reaches its maturity(adulthood)- Red giant phase and after that its ageing depends upon its initial mass ,either equals to mass of sun or more than that.

We can get an idea of death of a star from the table below:

Final Stage Final phase(adulthood) Ageing Condition for initial mass, if, Dying stage Death
Star Red giant Depends on initial mass Mass = Sun’s Mass White dwarf Dense lump of matter in space
Star Red giant Depends on initial mass Mass > Sun’s Mass Supernova Black hole( a neutron star)

Now we will discuss these phases one by one:-

# Red Giant Phase

This is the adulthood phase of the star. This stage is achieved when all the hydrogen in the core get converted into helium and eventually the fusion process get stopped, as a result the core begin to shrink under its own gravity. Due to this the whole equilibrium of the star get disturbed and to readjust it , the star begins to expand its exterior. Hence as a result it becomes enlarged and giant and its color changes to red.

This is an unstable phase of star’s life.

Now come to the other alternative phase i.e, white Dwarf Phase

# White Dwarf Phase

Now the death of the star depends upon the initial mass of a star. Here the initial mass is similar to that of sun, then the red giant star would lose its expanding outer shell and the only core remain behind.This small core then gradually shrink thus formation of other fusion reaction start taking place in which helium get converted into heavier elements like carbon, and an extremely large amount of energy is released.

3 4He                                ………Fusion…………>                 12C                   +         Tremendous Energy

Three Helium Nuclei                                      One Carbon Nucleus

The White Dwarf Star is a star of highly dense matter in the form of protons and electrons.Ultimately it will fade into space as a dense lump of matter.

# Supernova Phase

Here the Stars which have higher mass compared to sun end up in a more catastrophic way resulting in big explosion.The whole process is same as that of white dwarf phase but one difference lies , that during expansion of outer shell , the energy released is very high that makes the red giant star to explode with a brilliant flash like a nuclear bomb.This type of exploding star is called Supernova.

The energy released in 1 second of a supernova explosion is equal to the energy released by sun in 100 years.

The core which is left behind continues to contract rapidly thus forming a Neutron Star.

This Neutron Star composed material mainly in the form of Neutrons.

A spinning neutron star emits radio waves and is called a Pulsar.

So, finally we have seen that every star has a definite beginning and a definite end. The birth and death of a star takes millions of year.

Now, lets have a look about Black Holes.

What are Black Holes?

A black hole is an object with such a strong gravitational field that even light cannot escape from its surface.

Black Holes are formed by the indefinite contraction of heavy neutron stars under the action of their own gravity.

Black holes are invisible,they cannot be seen.The presence of a black hole can be felt only by the effect of its gravitational field on its neighboring objects in the sky.


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