skip navigation
Galaxy NGC4414 from HST Astronomy 162:
Introduction to Stars, Galaxies, & the Universe
Prof. Richard Pogge, MTWThF 9:30

Lecture 30: Active Galaxies & Quasars

Readings: Ch 27, sections 27-1 thru 27-5

Key Ideas

Active Galactic Nuclei
Powerful energy sources in the nuclei of some galaxies.

Types of Active Galaxies:
Seyfert Galaxies
Radio Galaxies

Power source:
Accretion of matter by Supermassive Black Holes

Galactic Nuclei

Galaxy Nucleus:

Normal Galaxies:

Active Galactic Nuclei

About 1% of all galaxies have bright active nuclei.

Bright, compact nucleus:

Rapidly Variable:

In general, about 30-50% of spiral galaxies show some level of activity in their nuclei, but only about 1% are truly dominant.

Discovery of Active Galaxies

1943: Seyfert Galaxies

1950s: Radio Galaxies

The Riddle of the Quasars


Named them Quasars, short for Quasi-Stellar Radio Sources.

The Riddle of Quasars: Solved

1963: Maarten Schmidt (Caltech) This led to a problem:

Cosmic Beacons

Quasars are the most luminous objects in the Universe:

Brightest Quasars:

The Active Galaxy Zoo

Most Active Galaxies are related to each other

Radio Loud: powerful radio sources

Radio Quiet: very weak radio sources

All types of AGNs share many characteristics. A problem of modern research is to sift through the similarities and differences to figure out how they might be related to each other.

What powers AGNs?

Properties that need to be explained:



The Black Hole Paradigm

The energy source of active galaxies is the steady accretion of matter onto a supermassive Black Hole.

Infalling matter releases gravitational binding energy

The Central Engine

Black Hole accretion is very efficient:

Rapidly Spinning Black Hole:

Some Nagging Questions:

How do supermassive black holes form?

How are they fueled?

Do most galaxies have supermassive black holes?

All of these questions make the study of Active Galaxies a very exciting area of current research. As an aside, it is the primary area that I work in.
Return to [ Unit 4 Index | Astronomy 162 Main Page ]
Updated: 2006 February 16
Copyright Richard W. Pogge, All Rights Reserved.