According to a new study conducted by Yahoo Research “a whopping 50% of all content consumed on Twitter is generated by only 20,000 users.” The study examined 260 million posts sent via Twitter “between July 28, 2009 and March 8, 2010 containing bit.ly-shortened URLs.”

As a summary of the report by Patricio Robles at E-consultancy.com notes, the study has two other major findings:

(1) That Twitter isn’t very “social“: individuals on Twitter follow back far less than they’re followed.

According to the researchers, “The Twitter follower graph, in other words, does not conform to the usual characteristics of social networks, which exhibit much higher reciprocity and far less skewed degree distributions, but instead resembles more the mixture of one-way mass communications and reciprocated interpersonal communications“.

(2) There’s significant fragmentation on Twitter. In other words, “Celebrities listen to celebrities, while bloggers listen to bloggers.” Even if this isn’t necessarily surprising, it does highlight the fact Twitter users organize themselves around subjects more than they do other people.