Welcome to Gaia! ::

hello i am new i want to be an anstronomer! i watched a documentary about these super massive black holes in the center of galaxys! would u agree on this?

The existence of super massive black holes is confirmed. We do know now that our galaxy has it(at least one)...the andromeda galaxy seems to have two of them.

How do we know it?
the rotation of stars at the center of our galaxy. the trajectories shown by them tell us that there must be some huge force ,forcing them to take such unique paths.

This is very likely. That would be the main reason why all the stars in the Milky Way are orbiting around the galactic center. Such a huge black hole would produce a gravity well large enough to make all those stars orbit around it. Also, there's a few dwarf galaxies orbiting around the Milky Way. Then this super black hole must be really huge!

Whats interesting is that when two galaxies collide and merge together, the two super-black holes also merge together to form an even bigger one!
This is supposed to happen to the Milky Way and Andromeda galaxy merging together in about 2 billion years.