1. A method comprising: by one or more processors of a set of machines, performing an analysis of a plurality of documents among which some documents each reference a common topic; by one or more processors of the set of machines, clustering the plurality of documents by topic into a set of document clusters that each correspond to a different topic and that includes a document cluster in which the documents that reference the common topic are grouped; by one or more processors of the set of machines, detecting that a first member of a social networking service has interacted with a first document in the document cluster, the social networking service storing a profile that indicates a type of relationship between the first member and a second member of the social networking service; by one or more processors of the set of machines, determining a rank of the document cluster, the rank representing a likelihood that the second member is interested in the common topic of the document cluster, the determining being based on the detecting that the first member has interacted with the first document and based on the type of relationship between the first and second members; and by one or more processors of the set of machines, presenting the second member with a reference to a second document selected from the document cluster based on the determined rank of the document cluster.