ABOUT STAR BIRTH AND DEATH

2. WHAT IS A STAR?
The word star is well familiar to us since nursery with help of
some rhymes i.e. “twinkle twinkle little star” . But it is very
important to know something about it in detail .First of all it
is a astronomical object and a luminous ball of gas mainly
hydrogen and helium which are held together by its own
gravity. We have seen many stars at night and we have also
seen them twinkling. So the question arises that why star
twinkle at night? But the answer is so simple, it is because of
the effect of the atmosphere. As the light of the star enters the
atmosphere it is affected by winds and also by the temperature
change which makes the star to twinkle. It is well known to us
that sun is also a star and is also the closest star to earth.
After sun, Proxima centauri or Alpha centauri is the closest
star to earth about 4.22 light years away. In next few slides
I will tell you about the life of star from starting to the end.

3. FORMATION OF A STAR!
The birth of a star takes place in some steps. These steps are
given below-
1. The Interstellar cloud
stars are born within cold and dense clouds of space dust
and gases. The formation of the star starts by the
disturbance of the cloud by some collision or a explosion like a
supernova.
2. The fragments are formed
the cloud becomes unstable and is broken into several
fragments and these fragments are of different size as well as
different mass. The larger and denser of these fragments
turn into tighter clumps when pulled by their own gravity.
Now these fragments turn into a protostar. Protostar is the
early stage of star where it still finds its mass from the
interstellar cloud.

4. 3. Protostar
now the gravity pulls the material into its core. Now Here the
density, temperature and pressure builds up.
4. Spinning disk
Now due to the density, temperature and pressure at the
center creates a gravitational pull which attracts more dust
and gases inward. Now it starts to spin blowing winds.
5. A star is born
due to this the protostar’s core become too hot and dense that
nuclear reactions take place and star becomes to shine. The
core produces outward pressure that balances the inward
gravitational pull and the star becomes stable. And finally
the original star is formed
This is how a star is formed. But these stars are also of different
sizes and of different temperature. So it is important to
classify them. The stars are of four types i.e red giant,
white dwarfs, blue super giants and super giants

5. THE DYING STAR!
As the stars are of different size, temperature and masses so
different stars dye differently-
1. Small stars
these stars are those which are half of the size of the sun.
the process of dyeing of these stars is very slow. Firstly the
fuel in the star runs out and it fades. Now the star begins
to shrink. The process continues and the light of the star
becomes dim. And finally fuel is used up and turns into
black dwarf.
2. Medium stars
these stars are those which are nearly same of the size of
the sun. these stars use hydrogen in its core and nuclear
fusion spreads outside the core. Nuclear fusion is a nuclear
reaction in which atomic nuclei of low atomic number fuse to
form a heavier nucleus with the release of energy. Now the
star starts to expand into a red giant. Now when the helium
runs out it becomes a white dwarf.

6. 3. Massive stars
these are those stars which are eight times more than the sun.
The end of these stars are in strange and violent ways. Here
the heat and pressure inside the core becomes so great that
nuclear fusion not only fuses the hydrogen to form helium but
also helium to create carbon and oxygen. Here the star
expands and becomes the largest star that is red supergiant.
The process continues, and the core generates the outward
pressure to resist force of gravity and it collapse creating a
super nova. The star destructs it self. But the core of the star
continues the same process. If the core is small it becomes a
neutron star but if the core is big then it becomes a massive
black hole. In the first picture it is the supernova then a
neutron star then a black hole.
So this was about the star, its formation as well as its ending. We
are completely dependent on stars as if a star dyes it can
create a massive destruction. It may be one day we will be
also a part of this destruction. As a star namely Spica can
undergo supernova which is only 240 light years away from
earth.