There is a central engine, perhaps a black hole in the center of radiogalaxies. That engine ejects the matter with the speed comparable with the velocity of light. The surrounding magnetic field interacts with the ejected plasma, brakes it and causes enormous radio emission. These objects are called radiogalaxies or quasars. They are the most powerful objects in the Universe. The distance to quasars is several billions light years. The brightest quasars can be considered as the markers, and their distribution on the sky can give us a glimpse of the large scale structure of the Universe.
The work done so far is presented in the VLBA Calibrator survey web page. Positions of more than 3000 quasars were measured and images in radio waves for about half of the objects are available at here.