Interstellar Medium- The total mass of gas and dust between stars.
Stellar Nebulae- A cloud of gas and dust where new stars are born.
Protostar- The birth of a star caused by dense regions in a nebula collapsing due to gravity. When the temperature reaches a high enough point, hydrogen nuclei undergo nuclear fusion to form helium nuclei. The huge amount of energy released keeps the star's core hot.
Main sequence star- The longest , most stable period of a star's life where it converts hydrogen to helium in its core, generating heat and light. The outward pressure caused by thermal expansion balances the force of gravity pulling everything inwards. The heavier the star, the shorter the main sequences period.
Red Supergiant- As the core runs out of hydrogen and helium, the force of gravity is stronger than the force of thermal expansion which causes the star to compress. This makes the core hot and dense so the outer layers expand. They cool, giving it the red colour. This is 100 times larger and 1000 times brighter than a normal sequence star. Largest star in the Universe.
Supernova- A dying star that explodes violently, producing an extremely bright object that can actually last for months. It emits visible light, X-rays and infrared radiation
Neutron star- If the mass of the supernova core is not enough, it forms a star made entirely of neutrons instead of a black hole.
Black hole- Created when a giant star undergoes a supernova, it's an object so dense that not even light can escape its gravity.