Panning over the Jewel Box

Several very bright pale blue supergiant stars, a solitary ruby-red supergiant and a variety of other brilliantly coloured stars are highlighted in this Hubble Space Telescope image of the famed Jewel Box, or NGC 4755. The huge range in brightness exists because the brighter stars are 15 to 20 times the mass of the Sun, while the dimmest stars are less than half the mass of the Sun. This is the first comprehensive image of an open galactic cluster with imaging extending far into the ultraviolet.