NGC 6397

This is a globular cluster called NGC 6397. It’s about 7,800 light-years away, one of the closest globular clusters to Earth.

The cluster’s blue stars are near the end of their lives, having used up their hydrogen fuel. They’re now fusing helium into heavier elements in their cores, a higher temperature process resulting in a blue color. The reddish glow in the cluster is from red giant stars that have consumed most their hydrogen fuel but have expanded in size. The myriad small white objects include stars like our Sun.

Image Credit: NASA / ESA

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