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Astronomers who studied two star clusters using NASA's Chandra X-ray Observatory and infrared telescopes discovered that the simplest ideas for the birth of star clusters cannot work. This composite image shows one of the clusters, NGC 2024, which lies in the center of the “Flame Nebula,” about 1,400 light years from Earth. In this image, X-rays from Chandra appear purple, while infrared data from NASA's Spitzer Space Telescope appear red, green and blue. A study of NGC 2024 and the Orion Nebula Cluster, another region where many stars currently form, suggest that the stars on the outskirts of these clusters have an older age than those in the central regions. This finding differs from what the simplest idea of star formation predicts, where stars manifest first in the center of a collapsing cloud of gas and dust when the density grows large enough. [See more photos here.]