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. Galax i es plural.  But how massive can stars get? It’s an important question in astronomy. We have a decent grasp of how stars like the Sun behave, but as you add more mass to them their behavior can get wonky. They can become unstable, pulsating and even undergoing explosions that are just this side of a catastrophic supernova .  Also, when massive stars explode they seed the galaxy around them with heavy elements like iron that they make during their lifetime. Those elements are necessary to make planets, and life.…