ASSIGNMENT 19

Abnormal Galaxies and the Universe

 

 

INTRODUCTION

            The previous unit discussed normal galaxies constituting the great majority of galaxies in our cosmic neighborhood.  While there are many things not yet understood about normal galaxies, there are even more mysteries associated with abnormal galaxies discussed in Chapter 23.  The answers to some of these mysteries may provide new understanding of physical laws governing our universe.  According to the distances deduced from redshifts, the most unusual of the abnormal galaxies are the quasars, emitting much more energy in an incredibly smaller volume than any galaxy known.  The time machine effect discussed earlier in this course indicates that the quasars may be galaxies in early stages of evolution.

 

            In the second part of this unit, Chapter 24, the focus is changed from individual galaxies to the universe as a whole.  The redshift-distance relation discussed in the preceding unit is re-examined in terms of what it says about our universe, such as how old it is, and how it originated.  The most widely accepted theory of the universe, the Big Bang theory, will be discussed in detail.  The Steady State Theory, a competing theory, will be discussed as an example of the role observations play in evaluating different theories.  Finally, we will see how the useful time machine effect permits us to see back almost to the origin of the universe when space was filled with gas at a temperature of thousand of Kelvins.

 

 

REQUIRED READING

Re-read Subsection “The Astronomical Time Machine” of Section 2.2 pages 22 and 23.

 

Read Chapters 22 and 23.

 

 

WRITTEN WORK TO BE SUBMITTED

PART I.           Recopy, answer and turn in the computational/essay and multiple-choice questions below:

 

1.         Read Section 22.3 and examine Figure 22-13 (Seyfert galaxy) along with Figure 22-12  “Camera 2” (Normal galaxy).  Use the figures and text to compare the appearance of the Seyfert galaxy to the normal spiral galaxy.  How different?  How the same?  Note that the Seyfert galaxy is farther away than the normal galaxy so its photo is a bit blurrier.

 

2.         (a)        How is synchrotron radiation generated?

 

            (b)        What evidence is there that radio galaxies generate radio waves via the synchrotron mechanism rather than the thermal mechanism?

 

3.         (a)        Describe the radio emission structure of a typical radio galaxy.

 

            (b)        What other kind of unusual objects outside our galaxy often show jet-like structures?

 

4.         (a)        Reviewing Chapter 21, what does each of the symbols in V = Hd represent?

 

            (b)        How did astronomers initially conclude that quasars were very far away?

 

            (c)        How do the angular sizes and redshifts of radio galaxies and quasars indicate that quasars are farther away than radio galaxies?

 

5.         Describe the “supermassive black hole” theory of energy generation in quasars and radio galaxies.  What is an accretion disk?

 

6.         Figure 2-8, page 22 to illustrates the time machine available to astronomers to see the universe as it was at different times in the past.  Explain with words how this “time machine” gives different views at different distances only if the universe is changing with time!

 

7.         (a)        Recopy Figure 23-8 (the lower row).  Which frame (left, middle or right) represents the distant 10 billion light year objects in Figure 2-8, page 22?

 

            (b)        How is the galaxy number density different for the 10 billion light yr objects than for the galaxies near to us?

 

            (c)        Describe the radio galaxy number density observations versus redshift (i.e., distance).

 

8.         If the 3º K radiation is thermal radiation from the Big Bang, was the Big Bang temperature 3º K?  Explain why or why not.  When was the 3º K radiation emitted?  Which frame of Figure 23-13 corresponds to the 3 degree Kelvin observations?

 

9.         Where and when were hydrogen and helium made?  Where and when were atoms of elements heavier than hydrogen and helium atoms made?

 

10.       (a)        What will happen to the expansion of the Universe in the far future if its average density now is less than 5 x 10-30 grams per cubic centimeter?

 

            (b)        What if it is more than 5 x 10-30 grams per cubic centimeter?

 

(c)        What force determines the future expansion or contraction of the universe?

 

PART II.          Recopy, answer, and turn in the multiple-choice questions below.

 

1.         In the equation, V=Hd, the constant H equals ________ where t is the age of the universe.

a.         t2

b.         t

c.         1/t

d.         1/t2

e.         The Hubble constant , H, is unrelated to the age of the universe.

 

2.         The Halley Olbers paradox explains __________ as due to ___________.

a.         why the sky is dark at night; the finite, young age of the universe

b.         the parallax of  quasars; the earth circling the sun

c.         the spiral arms of galaxies; meteorite impacts on them

d.         the radio emission of galaxies; Cepheid variable stars

 

3.         The Big Bang theory of the universe predicted the existence of which of the phenomena below while the Steady State did not?

a.         The spiral arms of our galaxy

b.         The red shift of distant galaxies

c.         The blue shift of distant galaxies

d.         The 3º K radiation

e.         The 3000º K radiation

 

4.         The Hubble constant is a constant in an equation relating __________.

a.         wavelength and frequency in galactic spectra

b.         the velocity of recession of galaxies and their distances

c.         the velocity of recession of galaxies and their redshift

d.         none of the above

 

5.         If the present day density of matter in the universe is great enough, the universe will __________.

a.         expand forever.

b.         stop expanding and start contracting someday.

c.         continue its present contraction.

d.         all of the above.

e.         none of the above