Monday, July 26, 2010

Galactic black holes

The source of energy for all these different types of active galaxy is almost certainly a black hole. When a typical galaxy was formed, some of the stars near the center fell together and merged to form a massive black hole. For perhaps 50 million years this black hole swallowed stars, gas and dust, emitting vast quantities of radiation as it did so. Then the matter at the core of the galaxy was used up and the quasar faded. Quasar activity flared up and died away in galaxies over a two billion year period.
Similar activity continued on a smaller scale thereafter. The various sorts of active galaxy that we see today may be similar objects but they are viewed from different angle
Although the galaxies move randomly within a cluster, the clusters are rushing apart from each other. This is revealed by their red shifts. The galaxies motion has no center; viewed from any galaxy, all other galaxies seems to be rushing away. The further away the galaxy, the faster it recedes. The speed of recession is 17 to 30 Km/ Sec for every billion light years of distance.