Hi guys

Currently I am studying in the us and I am a permanent resident. I would like to go to europe for my Phd.

So what do I need to do for that. As you guys know permanent resident cannot go away from the us not more than 6 months. But in this case , is there any provision so that I can stay away from the us more than 6 months. If so what do I have to do? Do i loose my permanent residency or not? Or do I still need to visit in every 6 months?

Honest answer please.

Thanks