HP researchers recently examined how popular a subject needs to get to be listed among trending topics on Twitter.

“You might expect the most prolific tweeters or those with most followers would be most responsible for creating such trends, but that’s not the case,” says Bernardo Huberman,  HP Senior Fellow and director of HP Labs’ Social Computing Research Group.“User activity and number of followers do not contribute strongly to trend creation and its propagation,” he revealed further.

Instead, says Huberman, “we found that mainstream media play a role in most trending topics and actually act as feeders of these trends. Twitter users then seem to be acting more as filter and amplifier of traditional media in most cases.”

Bernardo and other researchers analyzed 16.32 million tweets on 3,361 different trending topics between September and October 2010 to figure out what made a topic trend.

Among a few factors, retweets seems to be the key. Around 31% of trending topics are retweets, and more importantly, 72% of those retweets come from mainstream media outlet like @breakingnews or @nytimes. The Telegraph, ESPN, Breaking News and The Huffington Post all made the list of top retweeted users in at least 50 different trending topics.

Huberman & co. also wanted to know why some trends last longer than others. “We discovered very few topics stay much more that 40 minutes at the top, but those that do persist engage an especially diverse audience.” Huberman then added, “we showed that the distribution of long-time trends is predictable, as is the total number of tweets and their growth over time.”