The star-forming process begins when the cloud becomes unstable and breaks into fragments. Gravity pulls the material into fragments into an ever-tighter clump, and the clump slowly forms a sphere as it shrinks. Now a protostar, this star-to-be carries on shrinking, its core getting denser and hotter.
The clouds that give birth to the stars are cold and dense and consist mainly of hydrogen gas. The newly formed stars are huge spinning globes of hot, glowing gas - mainly hydrogen, with helium and small amounts of other elements. Much of this material is packed tightly into the stars' cores, and it is here that nuclear reactions release energy in the form of heat and light.
Stars are born within enormous, cold, dense clouds of gas and dust. The process of star formation may be triggered if something disturbs the cloud, such as a collision with another cloud with another cloud or a shockwave from a supernova explosion. Now unstable, the cloud breaks up into fragments of different sizes and masses. These fragments will eventually turn into protostars.
A protostar forms. Gravity pulls material into its core, where density, pressure, and temperature build up. The more matter the original cloud fragment contained, the greater the temperature and pressure rise as the protostar develops. The growing mass at the center creates a gravitational pull, drawing ever more gas and dust inwards. A bit like water going down a plughole, the material being pilled in starts to spin round. Po
Squeezed by the force of gravity, the protostar's core becomes so hot and dense that nuclear reactions occur, and the star begins to shine. The glowing core produces an outward pressure that balances the inward pull of gravity, making the star stable. It is now a "Man sequence star". But not all of the material from the gas cloud has been used to make a star. The leftovers form a spinning disc of gas and dust around the star. The debris may be lost into space, or it may clump together to form planets, moons, comets, and asteroids.
Like earth stars generate the force of gravity, which squeezes their hot cor. The more matter the star has, the greater the force of gravity and denser and hotter and denser the core becomes. The way a star dies depends on how much it contains and how powerfully its core is squeezed by gravity. Star makes heat and light by the process of nuclear fusion: hydrogen atoms in the core crash together to form helium, releasing energy. In small stars, when hydrogen in the core runs out, the star's light slowly fades away.
Stars die in four different ways, all of which are shown below. Our Sun, a typical star, will follow the third way of dying, but not yet - it has enough fuel to keep shining for 5 billion years. When larger stars die, they turn hydrogen into heavier chemical elements such as carbon and oxygen, which are later recycled to form new stars and planets.
Stars with less than half the mass of the sun fade away very slowly. Once the hydrogen in the core is used up, the star begins to feed off hydrogen in its atmosphere. But it doesn't generate enough gravity to use other elements as fuel, so it slowly shrinks to become a black dwarf. *BLACK DWARF* A star that used up its hydrogen, fades and extinguishes its light, to form a black dwarf.
When a Sun-like star has used up the hydrogen in its core, nuclear fusion spreads outside the core, making the star expand into a red giant. The core collapses until it is hot and dense enough to fuse helium, but eventually, it runs out of helium too. Finally, It becomes a dwarf, and its outer layers spread into space like a cloud of debris and form a planetary nebula.
Stars over eight times more massive than our sun end their lives in a strange and violent way. The heat and pressure in the core become so great that nuclear fusion can not only fuse atoms together to form helium and larger atoms to create elements such as carbon or oxygen. As this takes place, the star swells into the largest star of all: a supergiant.
The Sun is a nearly perfect sphere of hot, glowing gas. Its source of power lies buried deep in the central core, where a nuclear furnace rages nonstop, turning matter into pure heat and light. Slightly bigger than a typical star, the Sun is large enough to swallow 1.3 million Earths. It contains 99.8% of all matter in the solar system, and the force of gravity generated by enormous mass keeps the planets trapped in its orbit.