  The large availability of user provided contents on online social media
facilitates people aggregation around common interests, worldviews and
narratives. However, in spite of the enthusiastic rhetoric about the so called
{\em wisdom of crowds}, unsubstantiated rumors -- as alternative explanation to
main stream versions of complex phenomena -- find on the Web a natural medium
for their dissemination. In this work we study, on a sample of 1.2 million of
individuals, how information related to very distinct narratives -- i.e. main
stream scientific and alternative news -- are consumed on Facebook. Through a
thorough quantitative analysis, we show that distinct communities with similar
information consumption patterns emerge around distinctive narratives.
Moreover, consumers of alternative news (mainly conspiracy theories) result to
be more focused on their contents, while scientific news consumers are more
prone to comment on alternative news. We conclude our analysis testing the
response of this social system to 4709 troll information -- i.e. parodistic
imitation of alternative and conspiracy theories. We find that, despite the
false and satirical vein of news, usual consumers of conspiracy news are the
most prone to interact with them.
