Here's a great post from Neiman Lab exploring the relationship between social media trends, bias and news.
"Trends” is a great word, the best word to have emerged amidst the social media zeitgeist. In a cultural moment obsessed with quantification, defended as being the product of an algorithm, “trends” is a powerfully and deliberately vague term that does not reveal what it measures. Commentators poke at Facebook for clearer explanations of how they choose trends, but “trends” could mean such a wide array of things, from the most activity to the most rapidly rising to a completely subjective judgment about what’s popular.
But however they are measured and curated, Facebook’s Trends are, at their core, measures of activity on the site. So, at least in principle, they are not news, they are expressions of interest. Facebook users are talking about some things, a lot, for some reason. This has little to do with “news” which implies an attention to events in the world and some judgment of importance."