A lot of astronomers (that I've heard discuss this topic), seem pretty sure that what lies beyond the observable edges of this Universe, is more of the same stuff (planets, galaxies, stars, etc...).

It's almost a near certainty that there are portions of the Universe that have already expanded beyond our current observable range.

So what lies beyond that visible edge is simply just more of the same old everyday "stuff".

And that stuff is simply part of our Universe (but is un-observable, unless we develop warp drive).

However, if what you are really asking and wondering about is what is OUTSIDE of our Universe... (for example when a black hole punches a hole in the fabric of space and time, and it's matter exists our universe...)... then

that's an entirely different question (and different place)!