Madison Beer may be the next pop superstar. The 13-year-old singer signed a contract with recording giant Island Def Jam just months after Justin Bieber called her a “future star.” Def Jam represents Biebs and Rihanna. But Long Island teen Beer awaits a judge’s approval of the contract because she is a minor. The deal entitles her to 12 percent of net sales and a $50,000 advance for her first album, according to court documents. Since Bieber tweeted links to Beer’s YouTube videos in July, her rendition of Etta James’ “At Last” has topped a half-million views. Entertainment lawyer David Fritz, whose clients include Wyclef Jean and Marc Anthony, represents Beer. He did not return calls seeking comment.