Planets Around White Dwarfs

Planetary sytems that are in orbits that are greater than roughly a few AU should survive their host star's evolution off of the main sequence. Eventually the star will become a white dwarf, which is much dimmer than its progenitor. White dwarfs are thus attractive targets for planet searches, since it is easier to detect a companion close to the white dwarf. I have embarked on several attempts to find planets around white dwarfs and have looked at roughly twenty nearby objects to a high degree of sensitivity both on the ground and with the Hubble and Spitzer space Telescopes. So far I haven't found anything, but I'm confident that some white dwarfs actually show evidence of having planets. These white dwarfs are polluted with metals and some of them even have dust disks. These disks could be created by asteroids or comets being ripped apart by the gravity of the white dwarf.