INTRO...
Welcome to the world of STARS. Hello friends welcome to my blog and this brand new post .Today I am going to tell you about Stars , yes the complete life cycle of a star , that how it is born , what is the origin , and where does it ends . Full story of a star .In my earlier post I described about the origin of this universe , I told you about different theories related to the birth of universe .I hope you liked that posts and I hope that after reading that post you are curious to know about stars . Therefore I have brought this post to fulfill your curiosity . So lets begin the tour...
WHAT ARE STARS...
So before starting about the life cycle of a star , let me first tell you about what is a star .A star can be defined as follows-:
"A star is a massive , luminous sphere of plasma which is held together by its own gravity . "
Let me explain it . Basically this definition says that a star is a very large glowing body which is made up of plasma or gases , and which is held together in combined form by its own gravity . They are completely made up of gases and there is not a single piece of solid matter . It produces a large amount of energy due to nuclear fussion reaction which is going in it . The shine of star is due to this reason , that is due to thermonuclear fusion reaction in which hydrogen is converted into helium which produces a lrge amount of energy .
A lot of temperature is raised due to this reaction on the surface of the star . This temperature can be calculated by observing their color , like the stars with blue color are the hottest stars whereas the stars with red color are the coldest this because the star which is in blue color is completely made up of Hydrogen whereas the stars with red color contains carbon particles .
So the color of star can also be used to find out the composition of the star . The hottest star with the blue color can have the temperature up to 50,000 degree celsius .
BIRTH OF A STAR...
So after we know about what is star now we are curious to know about how the star is formed , what are the processes involved in the birth of a star .A star originates from the dark space and becomes a lightful object , which shines freely in space , for its life time. So basically a new star forms from the old stars . Similar to human beings as new babies are formed form their parents , same to this new stars are formed by the help of old stars . They are the next generation of the old stars . The star forming process is as follows....
"When a star becomes old and aged it ends its life by exploding itself . When this star explodes , a cloud is formed which contains the remaining components of the old star . We called it as "star dust" .They are also known as "nebulae" .It is cloud which contains helium and other heavy elements that were present in the old star . With the passage of time the cloud mixes with the gases in the surrounding and finally forms a new star."
To compress this star dust and initiate the gravity a lot of energy is required , which can be provided by many processes like supernova explosion which releases a large amount of energy in space .Galactic collisions can also trigger the star formation process . Emission of radio waves can also trigger the star formation .
As the star dust cloud collapses it breaks into smaller and smaller pieces . In each of these fragments , the collapsing gas radiates away the energy that is gained by release of gravitational potential energy .As the density increases , these fragments become opaque and becomes less efficient in radiating energy which raises the temperature of the cloud and inhibits further fragmentation , these fragements now condense to form the rotating spheres of gas which refer to as stars .
Stars of different masses are thought to form by slightly different mechanisms. The theory of low-mass star formation, which is well-supported by a plethora of observations, suggests that low-mass stars form by the gravitational collapse of rotating density enhancements within molecular clouds. As described above, the collapse of a rotating cloud of gas and dust leads to the formation of an accretion disk through which matter is channeled onto a central protostar. For stars with masses higher than about 8 M☉, however, the mechanism of star formation is not well understood.
Massive stars emit copious quantities of radiation which pushes against infalling material. In the past, it was thought that this radiation pressure might be substantial enough to halt accretion onto the massive protostar and prevent the formation of stars with masses more than a few tens of solar masses.[49] Recent theoretical work has shown that the production of a jet and outflow clears a cavity through which much of the radiation from a massive protostar can escape without hindering accretion through the disk and onto the protostar.[50][51] Present thinking is that massive stars may therefore be able to form by a mechanism similar to that by which low mass stars form.
END OF A STAR...
Now we know that how a star is born all the process related to the birth of a star . But now also the life cycle of a star is uncompleted , and will be not complete without the end of a star . S o now we are going to describe the end of a star means the death of a star .
After the birth of a star it begins to shine in the space and the process of star evolution takes place , this is the process by which the star changes over he period of time . But this change is very slow , therefore it could not be noticed by humans. It takes hundreds of of years to happen the changes .The lifetime of a star depends upon the mass of the star , the heavier it is the older it is .
Nuclear fusion is the main source of energy for the star , hydrogen is converted in to helium through this process and a large amount of energy is released which acts as the fuel for the star . But as the time passes the hydrogen of the star begins to reduce , and then the star starts to convert the helium into heavier elements like carbon , iron and the center is accumulated with the heavier elements.So the center of the star begins to contract as there is no force which can stop the contraction so when the core of the star contracts the heavier elements rushes into each other and a huge amount of energy and pressure is produced . Because of which the outer part expands and cools , which make the star a red giant or red super giant .
The next stage of the end of star depends upon the mass of star . Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula . Whereas the stars having the mass 10 times more than our sun , rushes out of the fuel they explodes forming a supernova , and at the end when the remaining iron particles generate the strong gravitational force and it starts to contract and there is no force which can stop the gravitational contraction of the star. It collapses to a point of infinite density .
Before this stage is reached within a certain radius , light itself becomes trapped , and the object becomes invisible and it becomes a "black hole" let me explain what is black hole...
"A black hole is a region of of spacetime of huge density where gravity prevents everything even light from escaping. "
So when supernova takes place it spreads a lot of elements into the universe , all the elements which are present in our universe are provided to us by these supernovas only.
These are also responsible for the formation of new stars , so this process in continuous , all the stars die and give birth to new stars .This cycle will kept on going till the universe remains.
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