Active Galaxies

Lesson Objectives To appreciate that some galaxies emit far more energy at some wavelengths that can be explained simply in terms of ‘starlight’. To recall the types of active galaxies. To show an understanding of the mechanism for producing large quantities of radiation from active galaxies.

What are Active Galaxies Galaxies emit radiation that can be seen in the electromagnetic spectrum. An Active Galactic Nucleus (AGN) is an area at the centre of a galaxy that has an above average brightness (luminosity) over the spectrum. These galaxies are called active galaxies. The area at the centre is powered by a supermassive black hole. The amount of material spinning around the black hole forms an accretion disc. The heat caused by its speed and the effect of it falling into the black hole produces enormous radiation across the electromagnetic spectrum.

Seyfert Galaxies These have bright spectral emission lines caused by either the accretion disc, or from highly ionized gas around the nucleus. Gas that rotates the black hole faster shows a broader emission line. Typically, seyfert galaxies are spiral or irregular.

Blazers Blazers are active galaxies that have jets pointing towards Earth. This is the effect of 'looking down' the jet of a blazer. It is difficult to make comparisons between blazers because of the angle from which we view them. When they are angled at 90 to 35 degrees we see them differently to when they're angled between 0 and 35 degrees to our line of sight. Because of this they are quite variable, emitting radio waves and x-rays.

Quasars Quasars are active galaxies emitting radio and x-rays. They have extremely large black holes at their centre and are moving away from us at extremely fast rates. They are the furthest and oldest objects we know of; some are as far as 11 billion light years away.

Apply your knowledge Questions What powers an AGN? How do astronomers find evidence for AGNs? What types of radiation can some galaxies emit? Briefly describe these galaxies... - Seyfert - Blazers - Quasars

Mark and correct in green Ideal Answers 1) An AGM is powered by a supermassive black hole 2) The detect the enormous amount of radiation emitted 3) (previous slides) Mark and correct in green

Whats the difference between a blazar and a quasar? A quasar is a very energetic and distant galaxy with an active galactic nuclei. A blazar is just a much more compact and energetic version of the same thing. Blazar's are usually associated with very small, dense galaxies with much more powerful nuclei than quasar's

More about Quasars These stand for quasi-stellar objects. They appear like stars but are actually very different. They are believed to be galaxies that emit large amounts of x-rays, ultra violet light and sometimes radio waves. Quasars are believed to be caused by matter falling into a black hole at the centre of the galaxies, causing jets of matter to shoot out at high speed. They show large redshifts in their light meaning they are moving away from us at very high speeds and are typically billions of light years away from us. They are the oldest objects that we know about. Quasars were first identified by their high redshift (how fast they are moving away from us) and emission of radio waves.

Construct Your Knowledge Research how Quasars were first discovered

Review •What are quasars? •How did we discover them? •What is special about them?