Stars

A star is a massive celestial body carrying out nuclear fusion within its core. There are approximately 100 billion stars in the Milky Way galaxy. They tend to exist at the centre of star and planetary systems, being orbited by one or more planets. Those systems generally share the name of the star(s) they host. Fully explored and inhabited star systems are officially named by the Galactic Astronomical Union while the rest are referred to by their Celestial Classification.

There are a number of different types of stars, and they are primarily classified based on physical attributes. New stars fusing hydrogen to helium are categorised as main sequence stars and are placed into a spectral class depending on their mass relative to Sol. Different spectral classes are visually distinct, as they emit different wavelengths of light. Stars that have depleted their useful hydrogen fuel begin fusing helium into further heavier elements, expanding in volume and eventually becoming either red giants or blue supergiants depending on their mass at the time of depletion. Once this new fuel is expended, the star "dies". Red giants tend to dissipate, leaving behind their inactive core in the form of a white dwarf. Blue supergiants tend to undergo supernovae, leaving behind either a neutron star or a black hole.