Thursday, July 29, 2010
Tuesday, July 27, 2010
Monday, July 26, 2010
Tuesday, July 20, 2010
Counts of galaxies show that the clusters are themselves grouped into” super clusters” chains and sheets separated by apparently empty voids, and measuring hundreds and thousands of millions of light years across. Whether this frothy texture of the universe was present in the gas from which the proto galaxies condensed, or whether the galaxies gathered into these structures after their formation, is still not understood.
At the heart of any nearby galaxies, and of the Milky Way, there seems to be great activity, hidden behind dense gas clouds. Stars are being whirled around by intense gravitations fields, and high energy X ray radiation is being emitted. In some galaxies there is even greater activity, and these can be detected at greater distances.
Many active galaxies are throwing out great jets of radiation together with charged particles which show up clearly at radio wavelengths the jets collide with the intergalactic gas and are halted to form puffs of radio emitting matter, called radio lobes, mainly consisting of fast moving charged particles but including a scattering of stars.
The most intense activity is showing by the quasars, the nearest of which is two billion light years from us. A quasar is a quasi-stellar object, that is it looks like a star, but radiates in other regions of the electromagnetic spectrum like a galaxy. Not only can we see more quasars at great distances, because they are so bright, but the really are more. Most are found so far away that their light left them about eleven billion years ago- only a few billion years after the Big Bang. The outpouring of radiation seems to come from a tiny region at the centre of a galaxy.