Stars and space

Galaxies  Galaxies were created when gravity pulled dust and gas together after the big bang. As the universe expanded, it cooled and uncharged atoms formed.                                               The life history of a star   -          Particles in clouds of dust and gas gather together from their own gravity. As the clouds merge they get more and more concentrated to from a protostar.   -          As the protostar gets denser, it becomes hotter. If it gets hot enough, the nuclei of hydrogen atoms and other light elements fuse together. This releases energy making the core of the star hotter and brighter.   -          The star then becomes a main sequence star. Energy released in the core keeps the core hot so the process of fusion continues. This causes radiation to flow out steadily from the core in all directions.   -          The force of gravity that causes the star to contract is balanced by the outward pressure of radiation from the core. These forces stay balanced until most of the hydrogen nuclei in the core have been fused together.   -          When the star runs out of hydrogen nuclei to…