NGC 6397 and NGC 6121: Two globular clusters located in the Milky Way.
Caption: These two Chandra images are part of a study that shows that globular clusters, some of the oldest known objects in the Universe, may be less mature in their development than previously thought. The amount of bright X-ray sources is an indication of where each globular cluster stands in its evolution. In these images, red, green, and blue represent low, medium, and high-energy X-rays detected by Chandra. NGC 6397 has a clear surplus of X-ray sources, suggesting that it is in its middle age, while NGC 6121 appears to still be in adolescence.
Scales: Left panel 2.33 arcmin across and
right panel 3.65 arcmin across.
Chandra X-ray Observatory ACIS Images