The Facebook News Ticker displays updates from Facebook Pages that you have "liked" and activity of your Facebook friends in real time. Going forward, Facebook also plans to display ads and sponsored stories in the ticker alongside regular updates.
The news ticker is integrated with the Facebook Chat window and, until now, the ticker was only visible if your browser width was greater than 1200 pixels. If you were accessing Facebook on, say, a netbook with a small screen, the News Ticker may not be shown to you.
That seems to have changed now. If the width of your desktop screen (or the browser window) isn’t large enough to accommodate the News Ticker, it detaches itself from the Chat window and becomes part of Facebook’s right sidebar.