0. Galaxies with Active Nuclei. Chapter 14:. 0. Active Galaxies. Galaxies with extremely violent energy release in their nuclei (pl. of nucleus). “active galactic nuclei” (= AGN).
Strong, broad emission lines from rapidly moving gas clouds near the black hole
Weaker, narrow emission lines from more slowly moving gas clouds far from the black hole
Supermassive black hole
dense dust torus
Quasar or BL Lac object (properties very similar to quasars, but no emission lines)
Emission from the jet pointing towards us is enhanced (“Doppler boosting”) compared to the jet moving in the other direction (“counter jet”).
The study of high-redshift quasars allows astronomers to investigate questions of
1) Large scale structure of the universe
2) Early history of the universe
3) Galaxy evolution
4) Dark matter
Observing quasars at high redshifts
distances of several Gpc
Universe was only a few billion years old!
Light from a distant quasar is bent around a foreground galaxy
two images of the same quasar!
Light from a quasar behind a galaxy cluster is bent by the mass in the cluster.
Use to probe the distribution of matter in the cluster.