There is a STRONG X-ray source in the constellation of Cygnus, Cyg X-1, that is now commonly accepted as being a black hole. There are many heavy "gravity lens" effects throughout the galaxy as well, as well as other localized X-ray sources...

...but as far as the center of the galaxy goes, yes. It is also commonly believed that there are super-massive black holes in the centers of all galaxies.

Black holes DO NOT "suck you in." They are merely the stellar remnants of a collapsing, super-massive star. They still have the same mass as they did before the collapse (well, after the outer parts were blown off in supernovae, that is; the mass remaining is that of what was left after that event occurred). Having the same mass, they have the same gravitational effect: gravity acts as a point source in any body having mass, and weakens inversely with the square of the distance you get away from it. Now, black holes are essentially singularities (point objects) with all the mass they had leftover smushed into that point. Gravity is still acting in regards to that amount of mass, which is the same whether or not the remaining stuff is the leftover star before or after its final collapse. Gravity doesn't care; but the effects are misleading. An object approaching the singularity would appear to be "sucked in," while in actuality it is just being attracted toward the point of gravity just like a satellite above the earth would be attracted back to earth if its orbital velocity slowed.

The difference is that in one instance we would see ourselves "falling toward" a surface, rather than "being sucked into" a something that we cannot see. It's all gravity. (And actually, in the case of the satellite, it is being attracted toward the point of mass at the center of the earth, but the surface of the earth gets in the way. We call that a "crash." Heh.)

And speaking of gravity, this brings me to another misconception. Black holes do emit radiation. It just can't leave. If you think about it, any body has an escape velocity that a ship taking off has to reach in order to escape from the surface. The more massive and dense the body, the greater "oomph" you need to get away. (The faster you have to go.)

Black holes are so massive and dense that the speed of light is not fast enough to escape its surface. (If it has a surface, heh). Thus we don't "see" it, but we sure do observe it's effects.

By definition, a black hole is a severe warpage of spacetime, which essentially is closed off from the rest of the universe. That's as easy as I can make it without diagrams and such.