STELLAR POPULATIONS
Stars in the Milky Way come in two main types, known as populations. The stars of Population I are found in the spiral arms and the galactic disc between them. They are generally brighter and hotter and contain greater amounts of heavy elements. Like all stars, Population I are dominated by the lightweight gases hydrogen and helium, but these heavy elements boost the rate of nuclear fusion in their cores – this is why Population I stars tend to shine hotter and brighter than Population II stars of a similar mass, but it also means they have shorter life spans.