What is a star?
A star is an enormous sphere of hot plasma — mostly hydrogen and helium — held together by its own gravity and powered by nuclear fusion in its core. Our Sun converts about 600 million tonnes of hydrogen into helium every second, releasing the energy that lights the entire solar system.
How a star ignites
Stars are born inside cold clouds of gas and dust called nebulae. When a region of the cloud collapses under gravity, the core heats up; at around 10 million °C, hydrogen nuclei begin fusing into helium and the object officially becomes a star. Below roughly 8% of the Sun's mass, fusion never starts — those 'failed stars' are brown dwarfs.
Why stars don't explode (or collapse)
A star spends its life in a balance called hydrostatic equilibrium: gravity pulls everything inward while the pressure of fusion pushes outward. The Sun has held this balance for 4.6 billion years and will keep it for roughly 5 billion more.
How stars die
Mass decides everything. Sun-like stars swell into red giants and shed their outer layers, leaving a white dwarf. Stars above ~8 solar masses die as supernovae, leaving neutron stars or black holes. The heavy atoms in your body — iron, calcium, iodine — were made inside dying stars.
You can watch the nearest star live in Cosmik's 3D solar system — the Sun at the centre, rendered with real physics-inspired lighting.