C2 Space & Stars til 3)Post main sequence star

Space
-The universe contains hundreds of billions of galaxies, which contain billions of stars.
-Stars with planet orbiting them are called solar systems
-Other objects in orbit around stars are asteroids(rocky with circular orbits) and comets(icy with eccentric(not specific shape) orbit)
-Planetary satellites in orbit could be natural shape moons or man-made.
Stars
Stellar Evolution
stars flow diagram img:
Stages of stellar evolution
1)Protostar
-The mass of dust and gas of the stellar nebula clumps together under the force of gravity before the start of nuclear fusion
-The irregular clumps of varying density, rotate and the undergo gravitation force collapse to form a large dense centre, called the protostar
2)Main sequence star
-Gravitational collapse heats up the star, causing it to start hydrogen fusion.
-Eventually, the star reaches equilibrium at which
/>The energy radiated by the star balances the energy produced in thermonuclear fusion - temperature is constant

The radiation pressure outwards from the core of the star balances the gravitational pressure tending to collapse the star-star is constant
-Greater the mass, shorter the main-sequence period, since it uses fuel quickly
3)Post main sequence star
-Once the H is used up, it has mainly He.
-The core then contracts, reducing its gravitational energy and increasing its temperature, which causes the star to expand and its outer layers to cool.
-A red giant(or red supergiant depending on mass) is produced
-The core of the red giant continues contracting, increasing the temperature till its's enought to start the He fusion to form Be, C and O nuclei.