I completely understand your anxiety, but perhaps you could think of this new student as a boon to your research/education. Perhaps I am way off base, but if a new hot shot came into my group I would be slightly threatened. However, even though you are developing into a competitive researcher, you are also in grad school to learn as much as you can from every source/experience that you can get your hands on. Like ktel said, you could bounce ideas off of this person, learn what they know, and benefit from a fresh perspective. Unfortunately, you will always encounter new hot shots, but it is better to learn how to work with them rather than waste time comparing yourself to them.