Solar system: Sun + 8 planets + dwarf planets + moons + asteroids + comets. Inner rocky planets; outer gas giants. Gravity provides centripetal force for orbits. For a stable orbit, as the orbital radius decreases, the orbital speed must increase, and vice-versa.
Star life cycle — Sun-sized: Nebula → protostar → main sequence → red giant → white dwarf.
Massive stars: → red supergiant → supernova → neutron star or black hole.
During the main sequence, the inward force of gravity is balanced by outward radiation pressure from nuclear fusion.
Elements heavier than iron are formed in supernovae. Our solar system formed from the remains of previous supernovae.