"When a star like our Sun reaches the end of its life and becomes a red giant, it consumes any inner planets and perturbs the orbits of the surviving planets and asteroids. A white dwarf is the end result of this stellar expansion and subsequent collapse. Objects wrenched out of their former orbits should, like the asteroids in question, occasionally drift close enough to the star to be pulled apart by its gravity. Such a star, showing the excess infrared signature of a circumstellar disk that is likely caused by the tidal disruption of asteroids, is called a ‘polluted’ white dwarf." - Steven Perez from Bookmarklet