Formation of stars
Stars vary in their composition and may be divided into generations. The first generation of stars, which were primordial megastars, were extremely large and consisted mostly of helium and hydrogen. However, second and third- generation stars have been smaller and richer in composition, as they were formed from the enriched by exploded megastars interstellar medium.
The first stars
The first stars in the universe may have formed only 200 millions after the Big Bang.They were made almost entirely of hydrogen and helium (the only two existing chemical elements at that time in the early universe, with 76% and 24% of hydrogen and helium respectively). As there were no other elements, gas clouds had to condense into extremely large clumps for the star-formation process to begin. Therefore, first generation of stars were extremely large and hot, 100 to 1000 times the mass of the Sun.
As pressure and temperature in massive stars are extremely high, nuclear reactions within them proceed rapidly. Thus, first stars perhaps lasted only for several million years before exploding as supernovae.
Star formation and life
As a rule, stars are formed in the regions rich with interstellar matter, such as gas clouds (nebulae). First of all, clouds of gas begin to concentrate due to the gravity. The more the concentration , the higher are pressure and temperature in the center of such cloud. Finally they become so high that the cloud collapses and nuclear reactions start. With the beginning of the nuclear reactions the star ignites and begins its existence. A star converts the hydrogen in its core into helium, releasing energy that escapes through the star and radiates out in space. As a result, we can see the stars' radiation in form of light.
Star's life, behaviour and evolution depend on the balance between its internal pressure and its gravitational force. The pressure of the escaping energy would blow the star apart if there were not for the force of gravity acting in opposition. However, as the star burns its hydrogen and more and more heavy elements such as iron are produced in its core, the balance gets lost. Finally, the equilibrium between internal pressure and gravity gets disrupted which leads to the star's explosion.
Death of megastars and black holes
The first massive stars exploded into supernovae, from which the new generation of stars have been formed. However, some of the first megastars may have exploded as hypernovae. These events associated with black-hole formation and violent bursts of gamma rays. Thus, it may be implied that the largest black holes which now lie in the centre of most or all galaxies have originated from the first megastars explosion.
Stars and life evolutions
During the course of their lives and deaths, the first megastars created and then dispersed new chemical elements into space. Nuclear fusion within hot star cores formed such elements as carbon, silicon, oxygen and iron. While during the explosion of megastars, heavier elements, such as barium and lead were formed. These elements were utilised by the second and third-generation stars, where more and more of heavy elements were created. Explosions of stars have returned the elements into interstellar medium. Consequently, galactic mergers and stripping of gas have led to further intergalactic mixing and dispersion. These processes enrich the cosmos until today and are essential for the development of the universe and, in particular, for the formation of rocky planets and life forms. For example, in the Solar system, the new heavier elements have been essential for the formation of the Earth and life.
Stars vary in their composition and may be divided into generations. The first generation of stars, which were primordial megastars, were extremely large and consisted mostly of helium and hydrogen. However, second and third- generation stars have been smaller and richer in composition, as they were formed from the enriched by exploded megastars interstellar medium.
The first stars
The first stars in the universe may have formed only 200 millions after the Big Bang.They were made almost entirely of hydrogen and helium (the only two existing chemical elements at that time in the early universe, with 76% and 24% of hydrogen and helium respectively). As there were no other elements, gas clouds had to condense into extremely large clumps for the star-formation process to begin. Therefore, first generation of stars were extremely large and hot, 100 to 1000 times the mass of the Sun.
As pressure and temperature in massive stars are extremely high, nuclear reactions within them proceed rapidly. Thus, first stars perhaps lasted only for several million years before exploding as supernovae.
Star formation and life
As a rule, stars are formed in the regions rich with interstellar matter, such as gas clouds (nebulae). First of all, clouds of gas begin to concentrate due to the gravity. The more the concentration , the higher are pressure and temperature in the center of such cloud. Finally they become so high that the cloud collapses and nuclear reactions start. With the beginning of the nuclear reactions the star ignites and begins its existence. A star converts the hydrogen in its core into helium, releasing energy that escapes through the star and radiates out in space. As a result, we can see the stars' radiation in form of light.
Star's life, behaviour and evolution depend on the balance between its internal pressure and its gravitational force. The pressure of the escaping energy would blow the star apart if there were not for the force of gravity acting in opposition. However, as the star burns its hydrogen and more and more heavy elements such as iron are produced in its core, the balance gets lost. Finally, the equilibrium between internal pressure and gravity gets disrupted which leads to the star's explosion.
Death of megastars and black holes
The first massive stars exploded into supernovae, from which the new generation of stars have been formed. However, some of the first megastars may have exploded as hypernovae. These events associated with black-hole formation and violent bursts of gamma rays. Thus, it may be implied that the largest black holes which now lie in the centre of most or all galaxies have originated from the first megastars explosion.
Stars and life evolutions
During the course of their lives and deaths, the first megastars created and then dispersed new chemical elements into space. Nuclear fusion within hot star cores formed such elements as carbon, silicon, oxygen and iron. While during the explosion of megastars, heavier elements, such as barium and lead were formed. These elements were utilised by the second and third-generation stars, where more and more of heavy elements were created. Explosions of stars have returned the elements into interstellar medium. Consequently, galactic mergers and stripping of gas have led to further intergalactic mixing and dispersion. These processes enrich the cosmos until today and are essential for the development of the universe and, in particular, for the formation of rocky planets and life forms. For example, in the Solar system, the new heavier elements have been essential for the formation of the Earth and life.
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