We’re moving into the realms of the true giants when we start to look at the biggest stars in the universe. Unlike planets, asteroids and other celestial objects that are too dark and too small to give away obvious clues to their presence from afar, these colossal balls of fusing hydrogen can bloom up to spheres so big that they’re difficult to comprehend, blazing multi-spectra radiation across interstellar space and making their exact location known by the massive gravitational influence they have over their local environment.
There are an estimated 100 to 400 billion stars in the Milky Way alone and because many are fairly easy to spot, we’ve been able to observe some serious contenders for the ‘biggest star’ accolade. VY Canis Majoris is huge beyond belief: this monster of a star is so big it would make our Sun seem like a pin-prick next to it. Found 5,000 light years from Earth, it has a radius of 1,420 times that of the Sun and was once thought to defy theory on the size and luminosity of stellar objects. However, since 2009 an even bigger star has been discovered. With a diameter of around 2.3 billion kilometres (1.4 billion miles), 400 million kilometres (250 million miles) wider than VY Canis Majoris, NML Cygni is a true intergalactic heavyweight. Placed at the centre of our Solar System, this stellar giant would swallow up the entire inner Solar System, including the asteroid belt, Jupiter and over half the distance between Jupiter and Saturn. You can fit a billion Earth-sized objects into NML Cygni and still have room left over. In terms of mass, too, it’s pretty hefty, weighing in at 50 times that of the Sun, more than enough to create a huge supernova at the end of its life cycle. For the most massive star though, we have to look to the Wolf-Rayet star R136a1. It’s found in a cluster of massive stars called R136, 165,000 light years away from Earth in the Large Magellanic Cloud. At a ‘mere’ 30 times the size of the Sun it’s no NML Cygni, but it has 265 solar masses and is a million times brighter than the Sun: if placed in the Solar System it would outshine the Sun by as much as the Sun outshines the Moon. R136a1 is thought to have been even more massive too, as much as 320 solar masses but has lost a significant portion of this since its birth. But if we’re talking about galactic-scale masses, it’s the objects that are sometimes left behind in the death throes of massive stars that steal the show.