What are all your options here?
Are you talking about one summer, and that's it, and then you'd be back? Or are you talking about studying this summer, then staying for years apart?
Does she have an option to come with you if you are going to be gone for years?
It seems like there's a lot of flexibility here, it doesn't have to be all one way or all the other.
The other obvious choice is considering adoption, but it doesn't sound like she'd be open to that.
How open is she to other types of compromise, in the short term?
I agree 100% with the above posters. Although it may seem harsh, you two decided to have unprotected sex and took the chance of conceiving a child. Now that it has happened you want to just abandone your child and the mother for your own career. She can't think only of herself now and I'm sure her plans have changed due to the pregnancy. Just because the baby is coming does not mean that your life is over. Yes, it causes a strain and yes it is difficult but you need to work around this challenge now. You need to figure out what would be best for all of you now not just what's easy and convenient for you. There are other ways of making your career work, you just have to come up with some new ideas. Remember it's not this child's fault so don't become resentful to the baby or the mother. You were equally responsible for this child and to place blame because your career paths may not be what you bargained for is not fair.
You know that s e x can lead to pregnancy...that being said, if your plans were as important as you state they are, you could have prevented that and you didn't. Now you have a child and it's no longer "ME" it's "WE". This baby and the mother of your child should now be your #1 priority. Priorities change. You have obstacles and you can overcome them. Make a new plan that includes all of you. Be there for her and your unborn child. That is the right thing to do.
Your priority is with your child (I am assuming it is yours?). Honor your commitments and the rest will fall into place, even if it takes longer to do so. Once you make a baby, everything changes...she can't walk away from this either. Don't see it as messing up your life--see it as an opportunity for growth and maturity. Sometimes our goals have to shift and change due to circumstances--even a sports injury can finish a career very quickly. Go to plan B now and you never know, plan A still may work out in the end, but at least you have done the honorable thing. You will be rewarded for that in life.