Basic concept of star
STAR : Clumps of dust and gas in a nebula come together due to their own gravity and from stars. There are millions of stars. Stars are made of hot burning gases. They emit light of their own. They are very large and very hot. Light takes about 4.3 years to reach us from the next nearest star proxima centauri.Brightest star outside our solar system is sirius,is also called Dog star.Star are self-luminous bodies that account for 98 percent of the material in the galaxy.The rest two percent consists of interstellar or galastic 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.Star forming matter is richer in hydrogen and helium.A star's colour indicates the temperature of its surface.Blue colour denotes maximum temperature .Then comes yellow, then red, etc.The life of a star is spread over billions of years .It begins to formby compression of galactic gas and dust.Compression generates heat which in turn causes hydrogen to be converted into helium in nuclear fusion, thereby emitting large amount of heat and light .Continued nuclear fusion over a period of times starts depletion of hydrogen and the helium core becomes increasingly heavy, resulting into swelling and reddening of outer regions.Such stars of gigantic dimensions are termed as red giants.If the stars is of sun's size, its becomes a white dwarf. Their central density can reach up to ten degree 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 is ten two the power fourteen grams per cubic cm.They are formed due to novae or super novae explosion.Stars having 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".
STAR : Clumps of dust and gas in a nebula come together due to their own gravity and from stars. There are millions of stars. Stars are made of hot burning gases. They emit light of their own. They are very large and very hot. Light takes about 4.3 years to reach us from the next nearest star proxima centauri.Brightest star outside our solar system is sirius,is also called Dog star.Star are self-luminous bodies that account for 98 percent of the material in the galaxy.The rest two percent consists of interstellar or galastic 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.Star forming matter is richer in hydrogen and helium.A star's colour indicates the temperature of its surface.Blue colour denotes maximum temperature .Then comes yellow, then red, etc.The life of a star is spread over billions of years .It begins to formby compression of galactic gas and dust.Compression generates heat which in turn causes hydrogen to be converted into helium in nuclear fusion, thereby emitting large amount of heat and light .Continued nuclear fusion over a period of times starts depletion of hydrogen and the helium core becomes increasingly heavy, resulting into swelling and reddening of outer regions.Such stars of gigantic dimensions are termed as red giants.If the stars is of sun's size, its becomes a white dwarf. Their central density can reach up to ten degree 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 is ten two the power fourteen grams per cubic cm.They are formed due to novae or super novae explosion.Stars having 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".
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