LOS ANGELES (Reuters) – Justin Bieber topped Billboard's "21 Under 21" list of the world's top young musical acts for the second year in a row, fending off stiff competition from British boy band One Direction. Bieber, 18, "remains more powerful in the pop universe than ever", Billboard said, having released two No. 1 albums in the last year – holiday set "Under the Mistletoe" and his latest pop album, "Believe". "Bieber is the supernova of teen pop stars with charisma, popularity and swagger to spare … it's Biebs' world, and we're lucky to live in it," the music publication said. …
