Unformatted text preview: and active galaxies can last for only a few billion years at most. Quasars tend to be found at great distances from us; there are no nearby quasars. When we look at quasars, we see them as they were billions of years ago. The number of them increases at greater distances, so that must mean they were more common long ago. The number of quasars peaks at a time when the universe was about 20% of its current age. Back then the galaxies were closer together and collisions were more common than today. Also, the galaxies had more gas that had not been incorporated into stars yet. The number of quasars was hundreds of times greater than the time closer to the present. At very great distances the number of quasars drops off. The light from the most distant quasars are from a time in the universe before most of the galaxies had formed, so fewer quasars could be created....
View Full Document
- Fall '10
- Astronomy, Black hole, accretion disk, quasars