Study_Guide_4.pdf PHYS 104-01
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Popular in Astronomy
This 3 page Study Guide was uploaded by Sophie Stella on Sunday May 15, 2016. The Study Guide belongs to PHYS 104-01 at University of St. Thomas taught by Dr. Ruch in Winter 2016. Since its upload, it has received 35 views. For similar materials see Astronomy in Astronomy at University of St. Thomas.
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Date Created: 05/15/16
PHYS 104: Astronomy Study Guide for test 4, theAstronomy final Galaxies, the Milky Way, and Cosmology Remember to review the material from the previous tests as well. Definitions Spiral Galaxies: Galaxies that are flat and disk-like, with arms and a central bulge or bar. Elliptical Galaxies: Galaxies in globular form, with less dust than a spiral galaxy. The Big Bang: The creation of all space and time. Quarks: Subatomic particles which make up photons and neutrons. Cepheids: Stars in the instability strip of the HR Diagram. Quasars: The centers of very distant galaxies. These are usually 1000x brighter than the Milky Way. There is evidence that none exist anymore. They must consume 17 solar masses to be as luminous as they are. Active Galactic Nuclei: Nearby galactic centers with quasar-like characteristics. The Cosmic Microwave Background: The fog before the photons escaped after the big bang. This is found at the edge of the detectable universe. New Material I. Galaxies A. Spirals (3 main components) (they make up about 75% of the large galaxies) 1. (1) Athin disk containing gas, dust, and stars. 2. (2) Acentral bulge of stars. 3. (3) Aspherical halo surrounding the entire thing, containing stars and star clusters. 4. Some spirals contain a central bar that rotates rigidly, connected to the arms of the galaxy. It is speculated that this is the type of galaxy the Milky Way is. B. Ellipticals (are generally found in clusters of other galaxies) 1. Are not disk-shaped. 2. Contain no gas or dust (so no star formation). 3. Are lacking in O and B stars, which die off more quickly. a. Spirals and ellipticals, however, both contain many M stars. 4. The stars have highly elliptical orbits, with no orderly motion. C. Irregulars 1. This category contains every other type of galaxy which doesn't fit into either of the categories. 2. They are usually small and dusty, but don't spin. II. Galaxy Evolution A. It is impossible to watch a single galaxy evolve, but we are able to see different galaxies in different stages of evolution. 1. If we look out into space, we are able to see galaxies at an earlier stage in life than they actually are currently, and this is because it has taken so long for the light to reach us. 2. If a galaxy is redshifted, that means it is moving away from us. If it is blueshifted, it is moving towards us. B. Edwin Hubble came up with a system for galaxy classification 1. Elliptical galaxies are labeled with an E and numbered according to their shape and size. 2. Spiral Galaxies are labeled with an S and also numbered accordingly. 3. Spiral galaxies with a central bar are labeled SB. C. Galaxy formation hypotheses 1. Collapsing cloud of gas (the Top Down model) (also the most probable) a. The early universe starts as hydrogen and helium. b. The places with higher densities begin to condense. c. As this cloud collapses, halo stars begin to form in clusters. d. The cloud has angular momentum, so it begins to spin and the centripital force flattens the gas into a disk. e. If the cloud has less angular momentum, it condenses into an elliptical galaxy. f. The star formation continues in the disk where there is gas, but not in the halo. 2. Hierarchical formation a. smaller galaxies sometimes merge together to form larger ones. III. Hubble's Law V=HₒD A. The further a galaxy is, the more it is redshifted (the faster it is moving away from us). 1. There is a relationship between velocity and distance. 2. Velocity is measured by the doppler shift (the amount it is redshifted), measured in km/s/Mpc. 3. This does not conclude that we are at the center of the universe, which is highly unlikely. B. The space between galaxies is increasing, but the space within galaxies is not, because they are held together by gravity. IV. The Big Bang A. The observable edge of the universe shows what objects looked like at the time of the big bang, and everything in front of it is shown at a time long ago but getting closer to current time as they get closer in distance. If we can find the expansion rate of the universe, we can find its age. B. How we imagine the big bang: 1. Time and space spontaneously come into existence. 2. Quarks form, but are too hot to fuse together. 3. About one second into time now: quarks begin to combine to form protons and neutrons. 4. The universe is opaque a. The density is too high for photons to escape. 5. About 380,000 yrs into time: light photons begin to escape the fog of matter. 6. High-density places in the fog become galaxies. a. Galaxies are found to have been formed in a sponge-like order, like bubbles with pockets of empty space between them. V. The Shape of the Universe A. Gravity warps space: this leaves three options for the universe on a large scale. 1. Closed a. Shaped like the rubber of a blown balloon. If you started travelling in any direction without changing course, you would eventually come to the same spot. 2. Open a. Basically a flat universe, which is highly unlikely based on. 3. Open, but with some curviture like the closed universe. B. Our measurements of the detectable edge of the universe surprisingly give evidence of an open, flat universe. VI. The Mass of the Universe A. All current models of the universe must include dark matter in order to work. 1. They include 30% matter (dark matter as well as other stuff) 2. They also include 70% Dark Energy. (This is where the theory for the Ether came in) B. We have no concept or understanding of this dark energy, or of dark matter. VII. The Fate of the Universe A. Escape Velocity, on a universal scale 1. If we are in an open universe, it will keep expanding forever. 2. if we are in a closed universe (if the universe has a critical density), it will shrink back down and the big bang will happen again. B. Data has shown that the universe is expanding exponentially (everything is accelerating further), which is why the open universe theory is plausible. 1. Eventually everything will be expanding so fast that gravity won't hold it together. Frequently missed questions from the last tests. 1. Over time spans of a few hours, stars in the northern sky, as seen from St. Paul: -Travel in concentric circles with Polaris at the center. 2. Over time spans of a few hours, stars in the eastern sky, as seen from St. Paul: -Rise from the horizon at a 45 degree angle. 3. The true value of a scientific model is: -Its ability to make accurate predictions. 4. Why wasn't Copernicus's heliocentric model of the solar system an immediate smash hit? -The predictions made by this model were no better than the predictions made by the Ptolomaic model. 5. Gallileo's run in with the church -Was largely a political issue. 6. My car is going 60 mph in a circle. Its acceleration is: -Not Zero 7. Newton showed us that the shape of the trajectory of a baseball thrown near the surface of the Earth: -Is really the very tip of a long elliptical orbit whose focus is at the center of the Earth. 8. The pre-solar cloud contained Hydrogen gasses, rocky compounds, Iron, and icy compounds. Which is the correct list in order of abundance, from least to most? -Iron, rocks, ice, Hydrogen 9. As the temperature of a blackbody emitter is decreased: -The peak of the blackbody shifts towards red and the total emission decreases. 10. What causes light from a star to doppler shift towards the blue? -The star is moving towards us 11. Consider the spectrum pictured. If the two stars were the same size, which would be brighter? -Star A 12. The greenhouse effect warms a planet because: -The atmosphere passes visible light from the sun but blocks infra-red light from the planetary surface. 13. The Earth's atmosphere: -Is transparent in the visible and radio and partially transparent in the infrared. 14. Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is: -Converted into an amount of energy equal to 4 million tons times the speed of light squared. 15. The spectrum of the sun is: -A blackbody with absorption lines superimposed. 16. Why does fusion in the sun release energy? -The mass of a helium nucleus is smaller than the mass of four hydrogen nuclei. 17. We measure the temperature of the Sun and other stars by: -Measuring the wavelength of their peak emission. 18. What will be the ultimate fate of a high mass star? -It will explode violently and its core will become a black hole. 19. If the real speed of light was slightly slower than we think: -our distances derived from the main sequence would be too large. 20. the more massive a white dwarf: -the smaller its radius 21. Carbon fusion occurs in high-mass stars but not in low-mass stars because: -Only high mass stars can fuse carbon.
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