I saw an interesting article on the BBC science pages today.
It seems that NASA’s Spitzer IR telescope has discovered a dust ring around the white dwarf situated at the centre of the Helix Nebula (IR pic of the nebula below)! Puzzling indeed as one would expect all dust in the system to have been blown away during formation of the planetary.
They surmise that the dust ring, which is a mere 35-150 AUs from the star itself must be formed by continuous impacts between comets within the system.
It may solve another problem scientists ran into while studying the nebula. It seems that the white dwarf is producing an unusual amount of x-ray emmissions. These new observations suggest that the emmissions may be caused by material from this dust disc falling onto the star itself.
Here is a link to the whole article: