Watch out, Pandora. The Swedish music streaming service Spotify launched in the United States on Thursday, offering users free access to its catalog of more than 15 million songs. The company is letting users stream music for free for six months, after which they will be capped at 10 hours a month. For $4.99 a month users can listen without ads, and for $9.99 they can access music from mobile devices. The streaming service has partnered with Facebook, allowing users to share songs they like. Spotify launched in Europe in 2008 and now has 10 million registered users, 1.6 million of whom are paying subscribers.