Life Cycle of Stars

Stars are formed from an enormous cloud of dust and gas in space.
In millions of light-years, the force of gravity continuously pulls these gases and dust together, leading to the formation of a ball-like object.
The majority of this gas is mainly hydrogen.
As more gas and dust is pulled into the object, it starts to spin.
As the object spins, the hydrogen atoms start to collide with one another. As a result of these collisions, the object's temperature starts to rise. This temperature rises continuously to over 10 million degrees Celsius. A chemical reaction called the nuclear fusion of the hydrogen atoms starts to take place. In this reaction, two atoms of hydron fuse or combine to form helium. After this reaction, the gas in the object starts to slow. At this stage, the object is called a protostar, and it is the first stage of star formation. The fusion that occurs is an exothermic reaction that gives off large amounts of heat.

After forming a star from a cloud of gas and dust called nebulae, the star remains in a period called the main sequence. This is where a star spends most of its life for millions of light-years.
A star depends on nuclear fusion throughout its life to produce energy and internal pressure that acts outward against the force of gravity to keep it in shape.
Once the supply of hydrogen runs out, the star's internal pressure reduces, and it can no longer withstand the force of gravity acting on it. This marks the beginning of its demise. Because of decreased internal pressure, the star begins to collapse inwards towards its core. The collapsed materials exert more pressure on the core leading to an increase in temperature. The increased temperature and pressure push the outer layers outward but for a short time. This outward push expands the star leading to the formation of a red giant. What happens after the formation of a red giant depends entirely on the initial mass of a star. For instance, the sun-sized stars form a white dwarf and then a black dwarf. The massive and supermassive stars explode through a supernova, forming neutron stars and finally the black holes.

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