JP Maheu, CEO of Bluefin Labs Twitter has acquired Bluefin Labs, a social TV analytics company that was founded in 2008, sources say.

Although we don't know the exact acquisition price, we were told this is Twitter's biggest acquisition to date.

(Presumably these sources were excluding Twitter's early stock aquisition of Summize, which would now be worth ~$800 million.)

Prior to Bluefin Labs, Twitter's highest acquisition (as far as we can tell) was TweetDeck for $40 million in May 2011.

Since Bluefin Labs has raised $20.5 million to date, we assume the price is between $50 and $100 million (or higher), a healthy return for its investors, Time Warner Investments, SoftBank Capital, Acadia Woods Partners, Bedrocket Media's Brian Bedol, Jim Pallotta, Redpoint Ventures, Dan Gilbert, Lerer Ventures, Kepha Partners and the National Science Foundation.

Twitter's move into social TV makes a lot of sense. It hired a Head of TV last fall and there's a strong correlation between people watching shows and tweeting about them. Just look at last night's Super Bowl. With the help of a lengthy blackout, it was the most social event to ever air. According to Bluefin Labs, the event racked up 30.6 million mentions on Twitter, Facebook, and GetGlue, up from 12.2 million one year prior.

In addition Twitter has been dubbed the new TV Guide by Ad Age, and it secured a multi-year partnership with Nielsen in December to produce the first-ever social TV ratings.

The ratings will use a standard metric and reflect how many times a program is mentioned on Twitter. They'll be available for commercial use during the fall 2013 TV season.

Earlier this year, Twitter's UK team published a report about how its users interact with TV.

A few slides from the deck offer a strong hint as to why Twitter is making this deal:

The relationship between Twitter and television is strongly symbiotic. Twitter users love talking about what is happening on TV, TV viewers love using Twitter to see other viewers‘ opinions.

Twitter is increasingly acting as the second screen to TV. In this publication we explore the links between these two screens. Twitter is the shortest distance between you and what interests you most.

This interest is expressed in a huge volume of conversation. 400 million Tweets are sent every day. As a result when events happen in the real world, they happen on Twitter.

More and more we’re ﬁnding this is true for TV. When stand-out moments happen on TV, spikes in related conversation happen on Twitter. In fact, according to Second Sync, 40% of all UK Twitter traffic at peak TV viewing time is about TV.

Through the two distinct phenomena of discovery and engagement, Twitter and TV drive each other in a complimentary cycle. For example, a hashtag on air can boost engagement by organising viewers to tweet and interact. In the other direction, a TV-related Trend, or Tweet in a user’s timeline, can drive discovery.

Twitter is a real-time, public mirror for both broadcast content and advertising. Every programme - and every ad - has a Twitter presence.

Integration of Twitter into TV content can further stimulate engagement and discovery.

Simply adding hashtags on air - or in ads - helps to organise and steer the conversation.

In advertising, we’re seeing that deeper integration of Twitter not only drives discovery and engagement but also drives increases in brand recall scores and other marketing goals

In the eyes of advertisers, Twitter is arguably the most important social network. Again, if you look at last night's Superbowl, 50% of ads that ran mentioned Twitter. Only 8% mentioned Facebook; none mentioned Google +.

Bluefin Labs offers detailed reports about which brands are discussed most on social media. It can provide Twitter the ammo it needs to hook advertisers by showing who needs to spend money to up their social media status, and who needs to spend money to maintain their place at the top.

We've reached out to both Twitter and Bluefin Labs and will update if either has a comment.