Just how massive can stars get? Maybe not *quite* as massive as we thought

Massive stars — I mean truly massive, with 20 or more times the Sun’s mass — are terrifyingly powerful. 

The energy they produce scales steeply with mass, so at the top end of this range stars can blast out so much light they can be seen in other galaxies with small telescopes, and would cook any planets they have to a crisp. They can light up entire nebulae, and when they explode at the ends of their short, violent lives they can outshine entire galaxies. Galaxies plural.