Elliptical galaxies - getting to the heart.

Literature data on optical and radio properties of nearby elliptical and spiral galaxies are examined in order to answer two questions: (1) why are the strongest radio sources always associated with elliptical galaxies rather than spirals, and (2) why some of the elliptical galaxies are powerful radio sources while others, with similar optical properties, are not. It is shown that, in general, the brightest galaxies are most luminous radio sources; however, the fact that a giant elliptical galaxy becomes a radio galaxy depends not only on its size but on small-scale processes which take place in the innermost few parsecs of the galaxy. The reason why spiral galaxies do not become radio sources is attributed to the fact that they have bulge components which are small compared to most elliptical galaxies and, thus, lack the parsec-scale radio cores which are characteristic of elliptical radio galaxies.