The evolution of radio-loud active galactic nuclei

Abstract

Black holes often 'radio-active' for a short time only Galaxies consist of more than just stars. In between the stars reside large amounts of gas and dust, from which new stars may be formed. Furthermore, in the very center of virtually all massive galaxies a supermassive black hole is hidden. Usually it\'s dormant, but from time to time this greedy monster is fed with fresh gas, which is accompanied with highly energetic phenomena, a state astronomers call __active__. Two powerful jets may then emerge from the black hole which, when encountering the interstellar gas, produce strong radio emission. These radio sources can reach sizes of millions of lightyears. I have shown that weaker radio sources also expand, be it slower than powerful radio sources, but still with a velocity of 10% of the speed of light. Previously it was assumed that all small radio sources eventually grow out to sizes beyond a million light-years. By combining the signal of a global network of radio telescopes, I have determined sizes of young radio sources. These sizes differed from predictions of current models, indicating that the majority of very young radio sources does not grow to sizes larger than a few hundred light-years.