The word "quasar" refers to a "quasi-stellar radio source." The first quasars were discovered in the 1960s when astronomers measured their very strong radio emissions. Later, scientists discovered that quasars are actually radio-quiet, with very little radio emission. However, quasars are some of the brightest and most distant objects we can see.
These ultra-bright objects are likely the centers of active galaxies where supermassive black holes reside. As material spirals into the black holes, a large part of the mass is converted to energy. It is this energy that we see. And though smaller than our solar system, a single quasar can outshine an entire galaxy of a hundred billion stars.
To date, astronomers have identified more than a thousand quasars.