Ejections and Explosions

The discipline of astronomy is replete with unconventional personalities. The Armenian astrophysicist Victor Ambartsumian (Figure 7.1), who had a highly respectable career behind him by the mid-twentieth century, was certainly one such character. In 1958 he presented a paper at the prestigious Solvay conference in Belgium on the role of activity in galactic nuclei in shaping the structure and evolution of the surrounding galaxy; he proposed that spiral structure is formed by ejections from the nuclei of galaxies and that, in extreme cases, new blue galaxies are “born” (ejected) from the centers of giant galaxies. This all seemed quite bizarre at the time but the concurrent discovery of radio galaxies and, several years later, of quasars gave support to the less radical idea that many galaxies appear to undergo sudden impulsive events involving mass ejection, often in two opposite directions.

This was an initial interpretation of the morphology of radio galaxies, where two enormous lobes of radio emission are often observed beyond and on opposite sides of the visible object, generally an elliptical galaxy (see Figure 5.4 of Cygnus A). An early model involved the explosive ejection of two oppositely directed clouds of ionized gas and relativistic particles that are confined by ram pressure of supersonic motion through an ambient intergalactic medium. The amount of energy involved in such events would be huge, much larger than the rest mass energy of one million suns directly observed as relativistic particles.