The open star cluster Pismis 24 in the Scorpius nebula NGC 6357 is approximately 8,000 light-years from Earth. The brightest object, Pismis 24-1, was initially thought to have a mass between 200 and 300 solar masses, making it the most massive known star in the galaxy, exceeding the estimated upper mass limit of 150 solar masses for individual stars.
However, higher-resolution images taken by the Hubble Space Telescope revealed that Pismis 24-1 is two stars, each with a mass of approximately 100 solar masses. Analysis of their eclipses shows they are almost identical, with temperatures around 42,000 K. Collectively, the pair are nearly 800,000 times brighter than the Sun.
Spectroscopic observations from Earth-based telescopes also revealed that one of these stars is a close binary system, too compact for even Hubble to resolve. This means that the estimated mass of Pismis 24-1 is distributed among these three stars, and although they remain among the most massive stars known, the mass limit is not exceeded due to their multiplicity.
The images of NGC 6357 were taken with Hubble’s Wide Field and Planetary Camera 2 in April 2002. Credit: Credit: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)
Banner image: The images of NGC 6357 were taken with Hubble’s Wide Field and Planetary Camera 2 in April 2002. Credit: Credit: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)
Image credit:
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