SPACE SERIES - 4

 LIFE CYCLE OF A STAR - 2

WHITE DWARF STAR :

                          A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. 

A white dwarf's faint luminosity comes from the emission of residual thermal energy; no fusion takes place in a white dwarf.

The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun.

 The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Williem Luyten in 1922.

YELLOW DWARF STAR :

                               G-type main-sequence star (Spectral type: G-V), often called a yellow dwarf, or G star, is a main-sequence star(luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective measures between about 5,300 and 6,000 k. Like other main-sequence stars, a G-type main-sequence star is converting the element hydrogen to helium in its core by means of nuclear fusion. 

The Sun, the star to which the Earth is gravitationally bound in the Solar system, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton - proton chain (4 hydrogens form 1 helium),converting about 4 million tons of matter to energy.

Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha centurai B,Tau ceti, and 51 Pegasi

 LIFE CYCLE OF G-TYPE MAIN SEQUENCE STAR :

          

RED DWARF STAR :

                                 A red dwarf is the smallest and coolest kind of star on the main sequence .

 Red dwarfs are by far the most common type of star in the Milky way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed.

 From Earth, not one star that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima centurai.

The nearest star to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way.