The small open star cluster Pismis 24 lies in the core of the NGC 6357 nebula in Scorpius, about 8,000 light-years away from Earth. The brightest object in the center of this image is designated Pismis 24-1; Hubble Space Telescope images of the star show that it is really two stars orbiting one another that are each estimated to be 100 solar masses, among the heaviest stars known. Photo Credit: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)
