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Introduction to active galaxies
The field of active galaxies is recognised as one of increasing importance. But how do...
The field of active galaxies is recognised as one of increasing importance. But how do we know there are different kinds of galaxy? What are active galaxies? How are they powered? This unit examines the different types of active galaxy and looks at the crucial role of the active galactic nucleus and the energy source at its heart.
By the end of this unit 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;
- give an account of an accreting massive black hole as the engine of the AGN and relate its luminosity to the mass accretion rate;
- outline some of the outstanding problems relating to the evolution of active galaxies.
- Current section: Introduction
- Learning outcomes
- 1 Overview
- 2 The spectra of galaxies
- 3 Types of active galaxies
- 4 The central engine
- 5 Models of active galaxies
- 6 Outstanding Issues
- 7 Unit Summary
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Introduction to active galaxies
Active galaxies provide a prime example of high-energy processes operating in the Universe. This unit introduces the evidence for activity from the spectra of some galaxies, and the concept of a compact active galactic nucleus as a unifying model for the observed features of several types of active galaxy. It also develops the key skill of applying arithmetic and simple algebra to solving scientific problems.
This course is an adapted extract fromt he course
Copyright & revisions
Originally published: Monday, 16th May 2011
- Creative-Commons: The Open University is proud to release this free course under a Creative Commons licence. However, any third-party materials featured within it are used with permission and are not ours to give away. These materials are not subject to the Creative Commons licence. See terms and conditions. Full details can be found in the Acknowledgements section.
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