Just how big can a star get? The biggest stars in terms of diameter are red supergiants J that swell to enormous sizes as their lives come to an end. As they begin to exhaust their fuel and go through internal changes, these stars brighten, swelling in size as their surfaces become cooler and redder. But if by defining the biggest star you simply mean the most massive, the answer is very different. The most monstrous stars of all are hypergiants, with many times the mass of the Sun. The most massive of all was discovered in a neighbouring galaxy of the Milky Way in 2010 – a hypergiant star with up to 230 times the mass of the Sun, called R136a1.
Fittingly, this stellar bruiser is a resident of the largest star-forming nebula in our Local Group – the Tarantula Nebula in the Large Magellanic Cloud (LMC). Looking at first glance like a detached portion of the Milky Way in far southern skies, the LMC is one of the largest and brightest of several satellite galaxies trapped in billion-year orbits around the Milky Way. Huge tidal forces are compressing its copious reserves of gas and dust to trigger the birth of new stars at a much faster rate than in our own galaxy, giving rise to the Tarantula Nebula.
Within this region, some 650 light years across, radiation from newborn stars excites the surrounding gas to glow intensely. The Tarantula Nebula is famously so large
