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8.1 Continuum spectra

Activity 4: General properties of quasars and power-law emission

0 hours 30 minutes

Read Section 1.3 of Peterson, up to and including the first two paragraphs of Section 1.3.1 by clicking the link
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7.8 Example 2 and questions

Example 2

Show that the synchrotron spectrum produced by a power-law distribution of electron energies N(E) dE = N0E−s dE, is described by

You may use the approximation that all the power
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7.3 Polarization of electromagnetic radiation

So far we have described electromagnetic radiation in terms of its wavelength, frequency and speed. It has another, sometimes important, property: polarization. Figure 10 shows the electric and magnetic field in a plane-polarized electromagnetic wave. In any electromagnetic radiation, the electric an
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7.2 Free-free radiation

The blackbody spectrum is emitted when thermally emitting matter is optically thick. Optically thin matter can also emit thermal radiation. Whenever a charged particle is accelerated it emits electromagnetic radiation. When the acceleration is due to the electric field of another charged particle the emitted radiation is called free-free emission or bremsstrahlung. (Bremsstrahlung is a German word meaning ‘braking radiation’.) The radiation emitted by an optically thin, ther
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6 The key questions

Some of the most important issues which astronomers working in this field are currently trying to resolve are:

  • How and when did the supermassive black holes at the centres of galaxies form?

  • What role did the central black holes play in the formation of galaxies?

  • To what extent are the observed differences between AGN attributable to the orientation at which we view them?

  • What governs the evolution of
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5 Distances in extragalactic astronomy

Recall Hubble's law:

This relationship between redshift, z, of a distant galaxy which is given by

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4.1 The Milky Way

Figure 1 showed two spiral galaxies: NGC 5548, which has an active nucleus, and NGC 3277 which does not. If we accept that AGN are the result of accretion on to supermassive black holes at the centres of the galaxies which harbour them, it is natural to ask the question whether galaxies like NGC 3277, which do not
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3.5 Example 1

(a) A gravitationally bound uniform density sphere, of radius r, is composed of a large number of subelements, with total mass M. Use the virial theorem,

The gravitational energy is given byAuthor(s): The Open University

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3.4 The Eddington Limit

Thus the observations require that a luminosity of around 100 times that of the entire Milky Way Galaxy be generated within a region with a diameter only about 1000 times that of the Earth's orbit! (A truly amazing statement.)

The most obvious mechanism for generating such enormous luminosity within such a tiny region of space is an accretion process, but instead of perhaps more familiar compact stars with masses ~M
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3.3 Luminosities

The issue of whether QSO redshifts are of cosmological origin was unambiguously settled by the work illustrated in Figure 5 (particularly the two leftmost panels). When sensitive enough observations are made, the galaxies in which the quasars reside can be detected. The relatively faint emission from the surroundi
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1 Meet your first active galactic nuclei

Figure 1 compares two nearby spiral galaxies of similar distance and type. NGC 5548, on the left, has a brighter nucleus than that of NGC 3277, on the right. This extra emission from the central regions of NGC 5548 is not generated by stars. Instead this light is thought to be ultimately powered by material falling
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Learning outcomes

By the end of this unit you should be able to:

  • recognise the terminology which is used to describe the properties and behaviour of active galactic nuclei (AGN);

  • manipulate numbers, algebraic symbols and mathematical functions in equations.


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Introduction

This unit begins by studying evidence leading to our basic hypothesis that active galactic nuclei (AGN) are accreting, supermassive black holes. It also covers some physics of radiation which you will need to be able to interpret the observed emission of AGN, and includes an examination of AGN.

You will be studying a young subject and there are fundamental issues which are still being vigorously debated by the experts and are subject to current research activity. Consequently, it is not
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Acknowledgements

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

The material acknowledged below is contained in 99% Ape How Evolution Adds Up, edited by Jonathan Silvertown. Published by Natural History Museum in association with The Open University (2008). Copyright © Text: The Open University. Copyright © Design and layout: The Natural History Museum. This book forms part of the Open University course S170 Darwin and evolution.
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6 Summary

Is a belief in God compatible with the science of evolution, or does the question itself confuse the respective roles of science and religion?

Activity

Now that you have worked through the study unit, try to answer the self asses
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5 The Scopes monkey trial

This section was written by Gary Slapper.

In 2007, Professor Michael Reiss, a Church of England priest and the head of science at London's Institute of Education, said that it is becoming more difficult to teach evolution in schools because of the spread of creationism. Similar debate has long been burning in the United States. Also in 2007, a creationist museum opened near Cincinnati, where children in animal skins play amid model dinosaurs, suggesting they once coexisted and th
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3 Evolution and religion

It would be a mistake, however, to suppose that the invalidity of the creationist hypothesis and the redundancy of any supernatural agency in the Darwinian theory of evolution by natural selection necessarily endorse atheism, as has been mistakenly supposed both by creationists and some evolutionists alike. That God has not miraculously created every species does not disprove the existence of a deity. In fact, Darwinian evolutionary theory is equally compatible with theism and atheism. Darwin
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Learning outcomes

By the end of this unit you will:

  • have gained an understanding of the debates and issues surrounding evolution and religion.


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Introduction

Modern scientific discoveries reveal over and over again that the popular belief associating Darwinism with science is false. Scientific evidence refutes Darwinism comprehensively and reveals that the origin of our existence is not evolution but creation. God has created the universe, all living things and man. Yahya, H</span><br><span class=Author(s): The Open University

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