... Where do the most massive stars form? Observational evidence indicates that the outskirts of developing open clusters of stars are primary locations. ... Visible in the image center are massive stars in the open cluster. ... The Horsehead Nebula . ... Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s. Ganymede: Torn Comet Crater Chain . ... The South Pole of Mars . ... Stars, like bees, swarm around the center of bright globular cluster M15. ...