How to get a cosmic champion?

Sorry if this is a noob question. Just got the game last Sunday, and I've been working on getting the exploration rewards for act 1. However, I can't, since I have yet to obtain even one cosmic champion to open up the cosmic gates. Is there something I'm missing? Once again, sorry if this is a stupid question. Even if there is a way to get a one star cosmic, it would really help. Thanks!