MCC PHS 142 M01 Astronomy Homework Ch.22-23      
Adj Prof Astronomy: Sam Wormley <>

Background Material

  Textbook - Read Chapters 22-23
  Textbook -
  Textbook -
      (take the Multiple Choice Quiz for for each chapter)

  Web - 
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Galaxies are sprinkled throughout the Universe. Only three galaxies
outside the Milky Way are easily visible to the unaided eye - the great
galaxy in Andromeda and the Large and Small Magellanic Clouds. These
are our nearest galactic neighbors. Although they re just down the
block by astronomical standards, they are so far away that the light
their stars produce today won't reach us for tens of thousands or even
millions of years. 

The farthest galaxies lie as far away as our telescopes can see. Some
of them may be 11 billion light-years away or farther. These galaxies
formed soon after the Universe itself was born. In theory, if the
Universe lasts long enough, the galaxies will all expand apart.
Eventually new star formation will cease for lack of raw material
(hydrogen and helium). Some of the stars will drift away, but some will
fall into giant "black holes" that lurk in the hearts of most galaxies.
Eventually, all galaxies will disappear from sight. But that is
probably more than 10 80 years into the future. 

Big Bang and the Seeds of Galaxies

Accompanying those minute fluctuations in radiation, scientists
believe, were tiny fluctuations of matter, or, more precisely, baryonic
matter, mainly hydrogen and helium gas. Gravitational attraction
between the atoms concentrated them into faint clouds of gas. As the
Universe expanded, the surrounding matter gradually thinned out, with
the result that the internal gravity of the gas clouds grew relatively
stronger. Slowly, then faster and faster, the clouds pulled in more and
more material from the surrounding medium. Eventually, the clouds began
to collapse under their own gravity, evolving into galaxies. About one
billion years after the Big Bang, the first galaxies and the stars they
contain were born. 

The Hubble Deep Field--"is basically a blank patch of the sky which if
you look at with a modest sized ground based telescope, at one of the
sky survey prints, you see almost or two galaxies. The
statistics [1500-3000 galaxies], the sheer numbers are impressive, but
by itself that s not really enough. We can count the galaxies in this
image and say, my god there s a lot of them, but we don t know what
they are. We need to understand what these galaxies are, we need to
understand how far away they are, what their properties are before we
learn anything about galaxy evolution from a picture like this". 

"How far away are these things? Are they little dwarfs nearby... are
they starforming protogalactic subfragments? What are they? Well, we ll
try to find out eventually and that s what this [Hubble Deep Field] is
meant to be a resource for".


Some scientists theorize that such supermassive black holes may form
when a young galaxy is only a mass of gas and contains but a few stars.
A star in the densely packed core explodes, its core collapsing into a
black hole which then grows rapidly, devour ring neighboring stars and
gas. Some of the gas sucked in by the black hole is transformed into
vast amounts of energy, particularly radiation at radio wavelengths. It
s this radiation we can detect with the aid of radio telescopes. 

Many astronomers think that quasars eventually settle down and become
radio galaxies--larger, elliptical structures that continue to emit
strongly in the radio region of the spectrum, but are no longer as
bright as their quasar precursors. Eventually these radio galaxies
might evolve into galaxies. Because of their brightness and distance,
quasars are used by cosmologists as beacons to estimate distances on
grand scales and to study faraway gas clouds, which absorb some of the
quasar's radiation. The characteristics of this absorption can reveal a
lot about the mass, density and composition of the intervening gas.
These gas clouds may be the stuff from which galaxies are condensing. 

Galactic Collisions


Abstract: Theories of how galaxies, the fundamental constituents of large-scale
structure, form and evolve have undergone a dramatic paradigm shift in
the last few decades. Earlier views were of rapid, early collapse and
formation of basic structures, followed by slow evolution of the
stellar populations and steady buildup of the chemical elements.
Current theories emphasize hierarchical buildup via recurrent
collisions and mergers, separated by long periods of relaxation and
secular restructuring. Thus, collisions between galaxies are now seen
as a primary process in their evolution. This article begins with a
brief history; we then tour parts of the vast array of collisional
forms that have been discovered to date. Many examples are provided to
illustrate how detailed numerical models and multiwaveband observations
have allowed the general chronological sequence of collisional
morphologies to be deciphered, and how these forms are produced by the
processes of tidal kinematics, hypersonic gas dynamics, collective
dynamical friction and violent relaxation.

Homework Problems

Note the answers to the odd (Conceptual Questions, Problems and
Figure-Based Questions) are in the back of your textbook. It is
strongly suggested that you do some of those in every chapter so you
have immediate feedback as how well you are understanding the material.
There are online multiple choice quizzes for each chapter of your
textbook. Goto then click on

  Your book
  Student Edition
  Choose a chapter
  Multiple Choice Quiz
You are expected to do all of your own homework. Statistical patterns
showing copying or collaboration will result in no credit for the
homework assignment for all participants involved. The Code of Academic
Conduct for Iowa Valley Community College District is found in the
Student Handbook.

Physical Science classes require the use of mathematics. If you don't
know algebra, you sould NOT be taking this class. If you need to review,
look at Introduction to Algebra
WolframAlpha is way faster than a scientific calculator.

There is little excuse for turning homework in late. You have a whole
week between classes to read the chapters and do the homework. Homework
one week late - half credit. Two or more weeks late - no credit. Do the
homework during the week, not in class! You got homework questions,
email me 24/7.  Even if you don't have a homework 
question, email me anyway!

Problem 1: 
Using you starwheel (planisphere) determine what constellation is
located at 8h 50m Right Ascension and +18 degrees Declination.

Problem 2: 
Using you starwheel (planisphere) determine what constellation is
located at 7h 57m Right Ascension and -29 degrees Declination.

Problem 3: 
Galaxy NGC 3077 looks like an elliptical galaxy, but is peculiar
because of two reasons: First, it shows whispy edges and scattered dust
clouds similar to M82, probably a result of gravitational interaction
with its larger neighbors. The equatorial coordinates are:

  Right Ascension:  10:03.3  (hours:minutes)
  Declination:     +68:44 (degrees:minutes)
Using your starwheel (planisphere), determine what constellation NGC 3077
is found.

Problem 4: 
Why are the HII regions around O stars generally larger than those
around B stars?

Problem 5:  Suppose an observer on a hypothetical planet
maps the distribution of globular clusters in the sky. The observer
finds that the globular clusters are evenly distributed throughout all
parts of the sky. Where is the observer's planet?

Problem 6: 
About how often do stars in the Sun's part of the galaxy catch up
with and pass through a spiral arm? Hint: it will help to make some
sketches and think this through.

Problem 7: 
Describe the evidence that there is a massive black hole in the
center of our galaxy.

Problem 8: 
Why are the young objects in the galaxy confined to a thin disk, but
the oldest objects, such as globular clusters, occupy a nearly
spherical volume of space?

Problem 9: 
The gas at a distance of 0.1 pc from the center of the galaxy has an
orbital speed of 700 km/s. Use Equation 22.2 of find the mass of the
material in the inner 0.1 pc of the galaxy.

Problem 10: 
What is believed to be the way the ring galaxies are produced?

Problem 11: 
Using a value for the Hubble constant of 71 km/s per Mpc, find the
recession speed of a galaxy at a distance of 40 Mpc (130 million

Problem 12: 
Using Figure 23.20 to find the orbital velocity of matter in the
galaxy NGC 3200 at distances of 30 kpc from the center. Then use
Equation 22.2 to find the amount of matter at this distance.