MCC PHS 142 M01 Astronomy Homework Ch.22-23 Adj Prof Astronomy: Sam Wormley <firstname.lastname@example.org> Web: edu-observatory.org Background Material Textbook - Read Chapters 22-23 Textbook - http://highered.mcgraw-hill.com/sites/0073512184/student_view0/chapter22/ Textbook - http://highered.mcgraw-hill.com/sites/0073512184/student_view0/chapter23/ (take the Multiple Choice Quiz for for each chapter) Web - http://edu-observatory.org/eo/galaxies.html Web - http://edu-observatory.org/eo/radio_astronomy.html Web - http://www.seds.org/messier/more/m081gr.html Web - http://www.seds.org/messier/xtra/ngc/n3077.html Web - http://nedwww.ipac.caltech.edu/level5/Arp/frames.html Web - http://nedwww.ipac.caltech.edu/level5/SPGA_Atlas/frames.html Web - http://antwrp.gsfc.nasa.gov/apod/archivepix.html Galaxies 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 nothing...one 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". Quasars 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 See: http://www.public.iastate.edu/~curt/cg/homepage.html 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 http://www.mhhe.com/fix 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 http://www.math.armstrong.edu/MathTutorial/ WolframAlpha is way faster than a scientific calculator. http://www.wolframalpha.com 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. email@example.com 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 light-years). 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.