A star is referred to a luminous sphere of plasma which is held together by its own gravity. It consists of the thermonuclear fusion of hydrogen and helium in its core and thus appears to shine. Astronomers often use the words 'birth' and 'death' of a star in order to explain the complex relationship between matter and energy resulting in a star.
According to NASA, astronomers opine that the stars are born in the dense molecular clouds of gas found in the galaxies. Dense regions in these clouds break down to give rise to "protostars". As a star gets so much contracted that its central core can burn hydrogen into helium, it attains the rank of a "main sequence" star.
For a certain period of time, the luminosity of a star is dependent solely on its mass. Stars appear to be ten times more massive and thousand times more luminous than the Sun. However, due to a limited supply of hydrogen in their cores, stars have a limited lifetime in their main sequence ranks. As a star's core supply of hydrogen expires, it sheds it blur form and starts turning red, eventually becoming red and more massive in form.
According to National Radio Astronomy Observatory, there are various types of stars in the universe. Most of them, including the Sun, are called dwarf stars and appear to be smaller in size. Bigger than them are the brown dwarfs, which grow almost 8 percent more than the mass of the Sun, while the yellow dwarfs are said to have 120 percent more mass than that of the Sun. The giant stars that are found rarely reportedly consist of a mass 100 times more than the Sun.
While brown dwarfs collapse under their own weight and eventually become dark balls of cold gas, the yellow dwarfs turn into red giant stars by the infusion of hydrogen and helium inside their cores. Eventually, the core stops fusing due to the iron present inside a giant star, turning it into a swelling mass of gas that finally explodes. This phenomenon is known as a supernova.
The massive star collapse into a stage where its gravitational pull becomes stronger than the speed of light. As light doesn't shine off its surface, it ultimately becomes a corpse that astronomers mention as a black hole.
