Massive Stars in NGC 6357 . ... Credit Copyright: CHART32 Team , Processing - Johannes Schedler Explanation: Massive stars lie within NGC 6357 , an expansive emission nebula complex some 6,500 light-years away toward the tail of the constellation Scorpius . In fact, positioned near center in this ground-based close-up of NGC 6357, star cluster Pismis 24 includes some of the most massive stars known in the galaxy, stars with nearly 100 times the mass of the Sun. ... NASA Official: Jay Norris. ...