But how do we know there are different kinds of galaxy? What are active galaxies? How are they powered? This course, Introduction to active galaxies, examines the different types of active galaxies and looks at the crucial role of the active galactic nucleus and the energy source at its heart.

Course learning outcomes

After studying this course, you should be able to:

• Explain how and why the optical spectrum of an active or starburst galaxy differs from that of a normal galaxy
• Explain how and why the broadband spectrum of an active or starburst galaxy differs from that of a normal galaxy
• Describe briefly the observed features of starburst galaxies and the four main classes of active galaxies (quasars, radio galaxies, Seyfert galaxies and blazars)
• Understand the evidence that indicates the presence of a compact active galactic nucleus (AGN) in active galaxies
• Explain why an AGN should emit broad lines, narrow forbidden lines and continuous radiation.