Elon Musk announced his new company xAI, which he says has the goal to understand the true nature of the universe.Jaap Arriens | Nurphoto | Getty ImagesElon Musk's artificial intelligence company xAI has raised $15 billion from investors, sources familiar with the matter told CNBC's David Faber. The funding adds another $5 billion to the $10 billion round CNBC reported on in September, which valued the startup at $200 billion. Sources told CNBC that a lot of the money will fund graphic processin...