Running android apps directly on ubuntu or gentoo I wonder if is it possible to run android applications DIRECTLY on a Linux distribution like ubuntu or gentoo?
I mean running the apps on linux without the help of virtualbox,simulators like genymotion, on google chroom...

is it possible to compile a linux kernel in such a way to do this?
if so, is there any guide to to describe the process step by step?

any help is appriciated
Yes, there is, though right now it's still experimental. It's called Anbox, and it uses kernel features to share the kernel between the distro and the Android system.

Oh, and no need to recompile the kernel at all.