Picture From: SPL
Astronomers have found that certain white dwarf stars have atmospheres which are very rich in the rocky elements (such as silicon) which comprise Earth-like planets. A white dwarf is the core of an initially much larger star, whose outer layers have been lost when the star expanded to become a red giant. Astronomers suspect that as the star expands, it perturbs the orbits of any planets around it, perhaps leading to collisions. Repeated collisions grind down the planets into smaller and smaller pieces of rubble until the star, now a white dwarf, is surrounded by a disc of dust and hot gas. This image depicts the various stages in this process. At the top we see the planetary system it its youth. In the middle, the star has become a red giant and some planets have started to collide. And in the last frame, we see the resultant disc surrounding the white dwarf.