The Star Formation: How A Star Born ?

Stars: Star is self-luminous bodies that account for 98 percent of the material in the galaxy. The rest 2 percent consists of interstellar or galactic gas and dust in an attenuated form. Stars are formed by gravitational contractions from these vast clouds of galactic gas and dust. Star-forming clouds are thousands of times denser than the normal interstellar gas. The star-forming matter is richer in hydrogen and helium.

The Star Formation: How A Star Born ?

A star's color indicates the temperature of its surface. Blue color denotes maximum temperature. Then comes yellow, then red, etc.
The life of a star is spread over billions of years. It begins to form by compression of galactic gas and dust. Compression generates heat which in turn causes hydrogen to be converted into helium nuclear fusion, thereby emitting a large amount of heat and light.

Continued nuclear fusion over a period of time starts depletion of hydrogen and the helium core becomes increasingly heavy, resulting in swelling and reddening of outer regions. Such starts of gigantic dimensions are termed as Red Giants.

If the star of sun's size, it becomes a White Dwarf. Their density can reach up to 10 grams per cubic cm. If the star is bigger than the sun but not more than twice as big, it will turn into a Neutron Star or Pulsar. Their central density 1014  grams per cubic cm. They are formed due to Novae or Super Novae explosion.
Stars having a mass greater than three times that of the sun, because of their great gravitational power, have contracted so much that they have developed super density of 1016 grams per cubic cm. 

It is so dense that nothing, not even light, can escape from its gravity and hence called 'Black Hole'.
Brightest star outside our solar system is Sirius, also called Dog Star.

Closest star of Solar System is Proxima Centauri (4.2 light years away). Then come Alpha Centauri (4.3 light years away and Barnard's Star (5.9 light years away).

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