Since light travels at a finite speed, distant objects are seen as they existed in the past. We see the Sun not as it is now, but how it was eight minutes ago. We see the nearby stars as they were several years ago. We see Andromeda, the nearest spiral galaxy as it was roughly two million years ago. Thus, the most distant objects that we see are the oldest objects that we can directly detect.
Quasars are the most distant distinct objects that astronomers have been able to detect.
In a region smaller than our solar system, a quasar emits more light than our entire Milky Way galaxy. Quasars are believed to be supermassive black holes, whose masses exceed that of a million Suns, and whose pull is swallowing gas and stars from their host galaxies. They shine brightly by converting the gravitational energy of the infalling material into light. The most distant quasars are seen at a time when the universe was one tenth its present age, roughly a billion years after the Big Bang . Since light from a quasar illuminates all of the material along its path to us, quasars serve as distant flashlights revealing the properties of the early universe.