NGC 6357
This nebula includes the open cluster Pismis 24. There are many massive stars in this cluster. One of the brightest stars in the cluster i, Pismis 24-1, It was thought to be the most massive star on record. The star measures almost 300 solar masses. It was later learned that it was a multiple system of at least three stars. These three stars are each near 100 solar masses. This makes them among the more massive stars on record.