Sunday, February 21, 2021

Psimis 24

Pismis 24 is an open cluster inside NGC 6357, an emission nebula located about 8000 light years away from Earth.

This cluster has been studied very carefully by astronomers, especially those interested in stellar formation and evolution models. In fact, several stars with a mass much higher than that of the Sun have been discovered inside it.

The brightest star in the image, Pismis 24-1, was in fact for a long time believed to be the most massive star ever observed. From its distance and brightness and from the stellar evolution models, a mass greater than 200 solar masses had in fact been obtained.

From the high resolution images taken by the Hubble Telescope, however, it was then understood that Pismis 24-1 is actually a binary (if not triple) star. According to the most recent observations, the two components of the system should both have a mass between 70 and 100 solar masses. The two components of Pismis 24-1 taken individually are therefore not even the most massive stars in the cluster: in fact, other stars with a mass of just over 100 solar masses have been observed.

Credit: NASA, ESA, Hubble, Jesús Maíz Apellániz, Davide De Martin. 

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