Sources adds background info, stuff that may not be apparent from the top results
Google is running a very interesting experiment with structured data, it is now adding a side panel with additional info for some searches, as some users have spotted.For example, a search for the artist Rihanna would surface the regular organic results, but also a panel dubbed 'Sources' on the right which contains info and facts on the artist pulled from various sources, hence the name of the feature, perhaps.
In the Sources box there's a photo of the artist, a short bio from Wikipedia and biographical info as well. Her top songs are listed too, with links, and there are thumbnails and to similar or related artists.
This is nothing that couldn't be found in the search results already, if you knew what to search for and where to look, but it wouldn't have been obvious from a generic search like this.
Her Wikipedia page is the top result organically, followed by her official website, so, presumably, all the info is there.
Google has been moving towards providing users with answers not just links and is providing direct info and answers where possible. But it has never done anything like this, it stuck to providing simple direct answers and info like the weather, stock quotes and so on.
'Sources' is not restricted to people, it can apply to several types of searches. Another example that Cyrus Shepard, who discovered the feature, has stumbled onto is a search for Twitter which prompted a Sources box with info about the company.
Its logo and Wikipedia entry were listed, as well where it was founded and where it's headquartered. There were some odd entries such as "Name" which only listed "Sign in" and "Category" which said "Private."
But the feature seems to be rather experimental and unreliable. The Twitter logo for example was not pulled from any official site but rather from some random blog, Shepard noted.
The feature is clearly build on Google's structured data efforts, like the retired Squares. But it doesn't seem like something that will see the light of day any time soon, at least not in this form.