Scientists say the practice of feeding biological material from cows to cows can spread the disease.

CNN: Democrats criticize administration over mad cow

"And based on the whole phenomenon of polluted white dwarfs and what we've learnt in the last few years, we know that there's a disc of material that must be feeding the star's atmosphere with this silicon-rich material, " he told BBC News.

BBC: 'Dirty' stars hint at Sun's future