"When astronomers survey the universe, the landmarks are galaxies, those gigantic agglomerates of stars and interstellar gas spread across the immensity of space. A typical spiral galaxy, like our own Milky Way, boasts hundreds of billions of stars grouped along hundreds of thousands of light-years. That means that it takes a beam of light all that time to go from one extreme of the galaxy to the other, traveling, as light does in a vacuum, at 186,282 miles per second."

"But galaxies are much more than what the eyes can see. Nested in their center are enormous black holes, some with masses equal to many millions of suns. Those behemoths gobble up matter around them, creating the bright "eyes" that we see in telescopic pictures such as this one. As matter falls into the black hole, it radiates energy, which telescopes of different types (from optical to radio and X-ray) detect."