PIX4564803: Globular cluster NGC 6397 in the Altar - Stars in globular cluster NGC 6397 in Ara - Image of the center of the globular cluster NGC 6397 located 8200 years - light in the southern constellation of the Altar. The density of stars is very important, the stars are distant from each other only a few weeks light (the star closest to our Sun is four years away - light). Sometimes a collision between two stars occurs; they merge into a single, young, bright and warm star called a blue straggler; some of these stars are visible near the center of the image. This Hubble Space Telescope view of the core of one of the nearest globular star clusters, called NGC 6397, located 8,200 light - years away in the constellation Ara. The stellar density is about a million times greater than in our Sun's stellar neighborhood. The stars are only a few light - weeks apart, while the nearest star to our Sun is over four light - years away. The ancient stars are so crowded together that a few of them inevitably collide with each other once in a while. Near misses are even more common. Even so, collisions only occur every few million years or so. When direct collisions occur, the two stars may merge to form a new star called a “” blue straggler”””; these hot, bright, young stars stand out among the old stars that make up the vast majority of stars in a globular cluster. Several such bright blue stars are visible near the center of the cluster in the image. This Hubble image is a mosaic of two sets of images taken several years apart by the Wide Field Planetary Camera 2 taken in 1997 and 1999 / Bridgeman Images