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 !
Sally Riordan, M.A., Management Consultant, London
'One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike - and yet it is the most precious thing we have.'