What do quasars tell us about the past of the Universe?

Question

What will be an ideal response?

Answer 1

Quasars are small and powerful sources of energy in the active cores of very distant galaxies. Some quasars are more than 10 billion light-years away, and because of their large look-back times, they appear as they were when the Universe was only 10 percent of its present age. The first clouds of gas that formed galaxies would have also made supermassive black holes at the centers of those galaxies' central bulges. The abundance of matter flooding into those early black holes could have triggered outbursts that are seen as quasars. The galaxies were closer together when the Universe was young and had not expanded very much. Because they were closer together, the forming galaxies collided more often, and you have seen how collisions between galaxies could throw matter into central supermassive black holes and trigger eruptions. Quasars are often located in host galaxies that are distorted as if they were interacting with other galaxies. Astronomers have discovered that nearly all galaxies contain supermassive black holes, and those black holes may have suffered quasar eruptions when the Universe was younger, galaxies were closer together, and infalling gas and dust were more plentiful. Quasar eruptions became less common as galaxies became more stable and as the abundance of gas and dust in the centers of galaxies was exhausted.