Information derived from APOD March and December 2016:
NGC 6357, the Lobster Nebula is home to unusually bright and massive stars. The overall blue(ish) glow near the inner star forming region at the centre of the image results from the emission of ionized hydrogen gas. The surrounding nebula holds a complex tapestry of gas, dark dust, stars still forming, and newly born stars. The intricate patterns are caused by complex interactions between interstellar winds, radiation pressures, magnetic fields, and gravity. The entire nebula, some of which lies out of frame, spans about 400 light years and lies about 8,000 light years away toward the constellation of the Scorpion.

The open star cluster Pismis 24 (above the bright area below centre frame) was once thought to contain a star (Pismis 24-1) with 200 to 300 times the mass of our Sun, making it one of the most massive stars known. It turns out that it's actually 2 stars with a combined mass of a mere 140 suns (Pismis 24-1 NE and SW). These stars appear as the single brightest star in the cluster located just above the bright gas front below centre in the frame. For a list of massive stars making up the Pismis 24 cluster see https://pbase.com/gailmarc/image/170843222/original.