Post by | Ghulam Muhammad Faiq | Class VA
LIFE OF A STAR
Stars are born in clouds of gas and dust called nebulae. Where the gas and dust are thicker, gravity starts to pull them inwards. It collapses into a ball called a protostar. As this gets smaller the temperature rises until the core is hot enough for nuclear reactions to begin. Hydrogen nuclei fuse together producing energy. This energy pushes the gases outwards against the pull of gravity and the star becomes a stable glowing ball. Leftover material swirls in a disc around the new star and condenses to make planets and the moon.
In very small protostars, with masses less than 8 percent of the Sun’s mass, the temperature never reaches the point where nuclear reactions can start. These become brown dwarfs that glow because they are hot but never produce energy like proper stars so they gradually cool down.
A star will shine steadily for millions or billions of years depending on its size. The Sun will shine for about 10 billion years. Eventually, the hydrogen fuel in the core will run out. Then the Sun will swell up into a huge red giant star and the outer layers will drift outwards leaving a small hot white dwarf star surrounded by a glowing cloud of gas called a planetary nebula.
GIANT STAR
A giant star with a mass about 100 times that of the Sun burns very brightly and quickly and will use up its hydrogen fuel in less than a million years. Then it will swell up into a red supergiant and very suddenly collapse and explode as a supernova. This explosion throws out a shell of glowing gas called a supernova remnant leaving a tiny hot star, called a neutron star, in the center. The biggest star continues to collapse until they become black holes.
The gas and dust from planetary nebulae and supernova remnants then become the materials for a new generation of stars.
