Astronomy Internet Activity Beyondthe Milky Way PDF

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Webquest “Beyond the Milky Way” Astronomy

Name: Adele Harris Part I: "Galaxy Types (review) & the Observable Universe" http://www.seasky.org/celestial-objects/galaxies.html

• List the four main galaxy types. Briefly describe each galaxy type. 1. Spiral Galaxy - flattened spiral disk with a bright center called the nucleus. 2. Barred Spiral Galaxy - much like a spiral galaxy, except the arms spiral out from a straight bar of stars instead of from the center. 3. Elliptical Galaxy - vary in shape from completly round to extremely elongated ovals; no bright center nucleus. 4. Irregular Galaxy - no discernible shape or structure. Divided into two classes IM & IO. - What are the differences between barred spirals “a” “b” & “c” and how is the Milky Way classified? • A - galaxies have short bar of stars extending from the center • B - galaxies have a medium sized bar of stars extending from the center • C - galaxies have a long, well-defined bar extending from the center - Which galaxy type is the most common in the universe – and why are they important? • Spiral Galaxy •

Describe the universe within 5 million light years of the Milky Way. http://www.atlasoftheuniverse.com/localgr.html • The Milky Way is one of three large galaxies belonging to the group of galaxies called the Local Group which also contains several dozen dwarf galaxies. Most of these galaxies are depicted on the map, although most dwarf galaxies are so faint, that there are probablt several more waiting to be discovered. - Name the three largest members of the Local Group. What type of galaxies are these? 1. Milky Way 2. Andromeda 3. Triangulum - Approximately how many dwarf galaxies are within the Local Group? How many stars? • Dwarf Galaxies: 46 • Stars: 700 Billion

- Why is it so difficult to detect dwarf galaxies? • They are so faint that they are hard to see - What are “galaxy remnants?" (scroll down). What is the name of the possible remnant dwarf galaxy that lies in the Milky Way? • Galaxy Remnants: nebula left behind after a supernova • Large Magellanic Cloud 3. Return to the atlas of the universe map. Click on the "Zoom Out x20" button and describe the image. • The map is much more clustered.

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- How far away (approx.) is the center of the Virgo Supercluster? Describe the Virgo Supercluster 35 million ly

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- How does the Local Group of galaxies fit in with this supercluster? The Local Group is quite small in comparison

- Click on the atlas map "Zoom Out HYPERLINK "http://www.atlasoftheuniverse.com/virgo.html"X HYPERLINK "http://www.atlasoftheuniverse.com/virgo.html"10" and then "Zoom Out HYPERLINK

"http://www.atlasoftheuniverse.com/universe.html"x HYPERLINK "http://www.atlasoftheuniverse.com/universe.html" 14" and describe each image • The number of super c,usters, galaxy groups, large galaxies, dwarf galaxies, and stars has increases greatly with each click. 4. Explain what is meant by "the observable Universe." • It means that it is possible for light and other objects to reach and be visable on Earth. - How big is the actual observable Universe thought to be? How do astronomers know this? • 46.508 billion light years - How big is the "unobservable" Universe thought to be? How do astronomers know this? • Geometry suggests that the universe may have a n infinate size and that is will expland forever.

5. Go to the interactive scale of the Universe. Describe what this scale shows. https://scaleofuniverse.com/

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The scale shows everything in size comparison to other objects. Microscopic to the size of the universe. - Briefly describe the scale in size of each image -helium nucleus, animals,

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buildings, mountains, planets, stars, nebulae, galaxies and the observable universe. (*Note "10E" describes scientific notation as in 1.7 x 10 -15 or .0000000000000017 meters!) Helium Nucleus: 10^-14.7 Animals: 10^0.6 Buildings: 10^2.4 Mountains: 10^3.9 Planets: 10^8.2 Stars: 10^10.5 Neblae: 10^16.3 Galaxies: 10^21.2 Observable Universe: 10^27.0

Part II: Hubble's Law http://www.physicsoftheuniverse.com/topics_bigbang_expanding.html

1. Explain why Einstein originally thought the Universe was "static" and unchanging. • Einstein assumed that the universe had the same gross properties in all parts and that it looked the same in every direction.

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- Why did Einstein change his mind as early as 1917? He realized that the equations of general relativity did not describe a static universe. - What did Einstein propose to keep his idea of a static & unchanging Universe? Cosmological Constant

2. How do astronomers use the terms "cosmological redshift" and redshift when describing objects in space? • Redshifts is used to describe the shift in distance between planets in space.

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- What did Edwin Hubble discover in 1929 about the farthest visible galaxies? Hubble discovered that the galaxies are moving away from us. - How did this discovery lead to the theory of a "Big Bang" start to the Universe?

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Due to Hubble's discoveries we realized that the galaxies were flying apart and were actually smaller in the begining.

3. What is the "Hubble Constant?" • The unit of measurement used to describethe expansion of the universe. - What are the two factors that could be slowing down OR speeding up the expansion of the Universe? Which factor is winning? • The General Theory of Relativity • Cosmic Repulsion - What does the term "megaparsec" mean and how fast does NASA estimate the rate at which the Universe is presently expanding? • Megaparsec: 3.3 million light years • 72 kilometers per seconds per megaparsec 4. State Hubble's Law in equation form and explain what is meant by each variable. • v = Ho d where: v = velocity of a galaxy, in km/s. Ho = Hubble Constant, measured in km/s/Mpc.

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- How did astronomers determine the latest value for the Hubble Constant? They based Hubble's new constant on a red giant star.

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- What is the age of the Universe based on the latest H0 value? 13.813±0.038 billion years

Part III: Active Galaxies HYPERLINK "http://imagine.gsfc.nasa.gov/science/objects/active_galaxies1.html"& HYPERLINK "http://imagine.gsfc.nasa.gov/science/objects/active_galaxies1.html" Quasars http://imagine.gsfc.nasa.gov/science/objects/active_galaxies1.html 1. Describe an "active galaxy." What makes these galaxies different from normal galaxies? • Active galaxies are galaxies that have a small core of emission embedded at the center of an otherwise typical galaxy.

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- What is thought to power active galaxies? Describe this process. The core as it is typically highly variable and very bright compared to the rest of the galaxy. - Briefly describe the three types of active galaxies below:

Seyferts - a galaxy of a type characterized by a bright compact core that shows strong infrared emission. Quasars - is an extremely luminous active galactic nucleus in which a supermassive black hole with mass ranging from millions to billions of times the mass of the Sun is surrounded by a gaseous accretion disk. Blazars - is an active galactic nucleus with a relativistic jet directed very nearly towards an observer.

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- What do all three have in common? How are they different? All of the above galaxies have an active nucleus

2. What is meant by "AGN?" Describe AGN's and how they are related to Quasars & Seyfert galaxies. • AGN: active galactic nuclei - Briefly describe the three parts or regions of an AGN below. Supermassive black hole - A supermassive black hole is the largest type of black hole, containing a mass of the order of hundreds of thousands to billions of times the mass of the Sun Accretion disk - An accretion disk is a structure formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Relativistic jets - An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as an extended beam along the axis of rotation. 3. Explain what "synchrotron radiation" (SR) is and how it is generated. • Synchrotron radiation is the electromagnetic radiation emitted when charged particles are accelerated radially "Synchrotron radiation is not dependent on the temperature of a given astronomical source; a relatively cool object can release substantial amounts of electromagnetic energy in this form. Synchrotron radiation is thus often termed nonthermal radiation."...