Template:POTD/2014-04-16
The star cluster Pismis 24 lies in the core of the large emission nebula NGC 6357, which extends one degree on the sky in the direction of the constellation Scorpius. Part of the nebula is ionised by the youngest (bluest) heavy stars in Pismis 24. The intense ultraviolet radiation from the blazing stars heats the gas surrounding the cluster and creates a bubble in NGC 6357. The brightest point of light above the centre of this image is Pismis 24-1, once thought to be the most massive known star but now known to be a binary system.Photograph: HST/NASA/ESA