1. A method for generating a stream of content for a user in real time, the method comprising: generating a model based on at least one interest of the user and at least one prior action from a group of heterogeneous data sources; receiving a request from the user for a real-time content stream; determining contextual cues surrounding the request including a time of day and a geographic location of the user associated with the request; retrieving fresh content items from the heterogeneous data sources based upon recency; storing and indexing the fresh content items in a real-time index; querying the heterogeneous data sources using search terms based on the real-time index and the contextual cues for a set of candidate content items; determining interestingness of each candidate content item to the user based on social relevance and an interest match of each item to the user; computing a first score for each candidate content item in the set using the model and based upon the interestingness of each candidate content item to the user; computing a threshold based at least in part on an extent of an increase in popularity within a geographic area and quality of content items having a similar subject in the geographic area; determining whether the first score for each candidate content item in the set exceeds the threshold; generating the stream of content in real-time from the set of candidate content items responsive to the first score for each candidate content item in the set exceeding the threshold; and adjusting the threshold based on activities including generating the stream of content.