Quasars are single spots of light in the sky that are actually further away than most of the galaxies we can detect. The fact that we can see them means that they must be spewing out absolutely enormous amounts of energy. At present, we can't be sure of the process behind this, but we do have a best guess - and that's where black holes come into the story.
It is plausible that there exist galaxies with huge black holes at their centre (about a billion times as massive as the Sun). In such cases, the black hole would suck in vast quantities of matter, and this would cause that matter to accelerate and heat up - so emitting trillions of packets of electromagnetic energy and creating the spectacle that we see in the night sky and call "quasars". At the moment, therefore, it is widely believed that quasars ARE black holes - super massive ones - or at least the swirling mass that surrounds them !
Answered by:
Sally Riordan, M.A., Management Consultant, London
'For the sake of persons of ... different types, scientific truth should be presented in different forms, and should be regarded as equally scientific, whether it appears in the robust form and the vivid coloring of a physical illustration, or in the tenuity and paleness of a symbolic expression.'