What is in the center of our galaxy?
No body really knows, but the most likely answer is a super massive black hole.
We have no idea what a black hole really looks like, as we have never taken a photo of one and most depictions (apart from the one from Interstellar) are incorrect, depicting it as a 2 dimensional shape in a 3 dimensional universe- so it would be a sphere (of sorts) like in Interstellar. Don't forget the fact they reflect NO light, so you can never actually see them.
Most scientists agree that a super massive black hole sits in the middle of most galaxies, slowly sucking everything up around them, although some of this matter does go fast enough that it will orbit the hole like a moon does a planet.
Hope this helps!