Q&A: Black Holes

Q:
"First, research over the past few years has shown that the mass of the supermassive black holes at the centers of galaxies is less than a percent of the mass of their host galaxy."

What research yielded this evidence or idea. How is it possible to measurer the density of a black hole, let a lone a supermassive black hole. Remember, black holes may be portals, or doors, or anything. If everything being "sucked" into a black hole, the majority of the mass would be at the end of this black hole... and if there aren't any differences in mass from the front to the rear of the black hole, common sense would say, its obviously going somewhere else.

A:
The research involves looking at the motions of stars in the centers of galaxies. These motions imply a dark, massive body whose mass can be computed from the speeds of the stars. The matter that falls into a black hole adds to the mass of the black hole. Its gravity doesn't disappear from the universe.