Massive Stars

- Evolution of Massive Stars

The evolution of stars which have a mass 5 or more times than M☉ ( solar mass ) have several stages of nuclear reactions after the formation of the red giant.

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- Formation of protostar

When huge gaseous clouds of hydrogen contract due to gravity, there is an increase in density leading to increase in pressure. The cloud finally contracts having a spherical mass made of hydrogen at its core and is now called a protostar. 

- Formation of steady star

A steady star is formed from a protostar due to the nuclear fusion of hydrogen to form helium. The energy released tries to expand matter in the star.
Eventually, the outward push due to the radiation generated during the expansion balances the inward gravitational pull. The protostar reaches a steady state and is called a steady star.

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- Formation of Red giant

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The process of fusion continues and this results in the formation of a helium inner core. The inner core is surrounded by hydrogen which continues to fuse at a rapid rate to form helium. 
The energy released causes the star's outer envelop to expand and therefore cool. The colour of the star changes to red and the star is called a Red giant.
The star's envelop expands while its core contracts resulting in a very high temperature of about 10^8 kelvin resulting in the fusion of helium in the core to form carbon.  Once the fusion is complete, the core cannot contract further.
The outer envelop of the red giant gets detached and it is thrown into outer space. It forms a cloud of hydrogen gas called Planetary nebula. 

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- Further nuclear reactions

The Carbon core produced ignites further to produce a core of oxygen. 
The chain continues leading to the production of heavier elements like magnesium, silicon, iron etc. When a new core is formed, it is placed to the inside of the existing core.

- Supernova

When iron forms the innermost core, the star explodes and the event is called supernova.
During supernova, most of the materials are thrown out at speeds 10^4 km/s. A sphere of neutrons called neutron star remains at the center.  The The supernova initially looks like a nebula. It gradually mixes with other gaseous clouds, to initiate star formation.
The stars formed this way will be made up of elements heavier than hydrogen and helium.

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- Black hole

When supernova occurs for stars whose masses are about 30 times the mass of the Sun, a huge amount of matter is compressed into a small region.
This region has intense gravitational field and is called a black hole.

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Dark Blue

Blue

Bluish White

 White

Yellowish White

Yellow

Orange

Red

Colour of the stars

The Spacestellar Creations