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64 Cards in this Set
- Front
- Back
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Central Bulge
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center of the galaxy
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Nucleus
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At the very center of the central bulge; 4 million molar suns black hole
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Disk
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the "arms" of the galaxy; contains stars, clouds of gas, and dust
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Dust
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Microscopic solid grains that absorb visible light and limits how far we can see with visible light
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Halo
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Outer ring of our galaxy
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Where is the sun located?
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middle of the left disk
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How far is the sun located from the center of the galaxy?
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8.5 kilo-parsecs or 8,500 parsecs
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How far is the outer edge of the galaxy from the center?
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15,000 parsecs or 15 kilo-parsecs
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Who was the first person to realize that we were not at the center of our galaxy?
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Harlow Shapely
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How did Shapely figure out we were not at the center of our galaxy?
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He saw a large concentration of Global Star Clusters toward Sagittarius, estimated the distance the to center of the galaxy by estimating the distance to the clusters by using Pulsating Variable Stars.
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Pulsating Variable Stars
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Stars that pulsate in size and brightness
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What direction is the center of our galaxy?
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Sagittarius
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What discovery by Henrietta Leavitt allows Pulsating Variable Stars to be used as "distance indicators"?
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There is a relationship between the period of pulsation and luminosity
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What is one way to study the entire galaxy?
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Radio Waves
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Why can we "see" all the way across the galaxy using radio waves (but not visible light)?
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Dust absorbs the visible light
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How does a neutral hydrogen atom produce radio waves and what is the wavelength of this emission?
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protons and electrons can spin in the same direction and then in opposite directions; 21 centimeters
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What is the rotation curve for our galaxy?
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Very squiggly (remember graph)
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What is a rotation curve?
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A rotation curve is a graph of the orbital velocities of stars around the galaxy versus their distance from the center of the galaxy
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What does the actual rotation curve tell us about the very center of our galaxy and the halo of the galaxy?
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center: There is a large concentration of mass at the center of the galaxy (stars and black hole)
halo: There is much more mass in our galaxy then we though (90% of galaxy's mass is in the halo & stars are moving too fast) - "Dark Matter" |
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What is going on at the center of the galaxy?
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There is a large amount of energy produced at teh center of the galaxy
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We can study the centerer of the galaxy using what?
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Radio waves, X-Rays, and Infrared
NOT visible light because of dust! |
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What are the three main types of galaxies?
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Spiral, elliptical, and irregulars
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What are the properties of spiral galaxies?
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Have young and old stars and clouds of gas that form new stars
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What are the two kids of spiral galaxies?
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Normal (2/3) and Barred (1/3)
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What type of galaxy is the milky way?
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Barred spiral
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What is the most numerous type of galaxy in the universe? Why?
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Elliptical galaxies because there are many small ellipticals, called "dwarf ellipticals"
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What are the largest galaxies called? Where are they usually found?
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Supergiant ellipticals; at the centers of large clusters of galaxies
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What are the properties of elliptical galaxies?
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Generally round, only have old stars and do not have clouds of gas
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What are irregular galaxies like?
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These tend to be small galaxies with no definite shape; they have young and old stars and also clouds of gas
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It is thought that irregulars may have suffered a near collision with a bigger galaxy which nearly...
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tore them apart, giving them an irregular shape
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Three types of active galaxies
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Radio, Seyfert and Quasars
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What is the main source of the energy at the center of each of these active galaxies?
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Gas falling into a super massive black hole
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Where is the radio galaxy phenomena usually found?
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Elliptical galaxies
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What are the "radio lobes" and where are they in relation to the galaxy?
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Strong radio emitters located at the ends of the galaxy
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How big are the radio lobes?
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very large
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What are the jets?
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the usual sources of high-frequency synchrotron emission
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Where does the Seyfert galaxy phenomena usually occur?
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Spiral galaxies
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Characteristics of the seyfert galaxy
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A very bright, blue nucleus; a spectrum of the nucleus shows strong, broad emission lines of hydrogen and other elements
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What are the quasars?
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most extreme active galaxies, some of the most distant objects in the universe, happened early in the universe and are not happening today (there was a lot more gas to fall into black holes
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What was one of the first discovered quasars and what was it like?
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3C273; it appeared to be a bright blue star, but it produced large amounts of radio waves. It has an emission line spectrum but its lines were not immediately recognized
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Who discovered what the emission lines were?
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Maarten Schmidt
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What did Maarten Schmidt discover?
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Quasars
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As a quasar ages, what 2 types of galaxies might it become?
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Spiral or barred galaxies
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What does the Hubble Law say about (1) the motions of almost all galaxies with respect to us and (2) the velocities of galaxies and their distances from us?
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1) Essentially all galaxies are moving away from us
2) The farther away a galaxy is from us, the after is moves away from us |
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How can we understand the Hubble Law in terms of an explosion? An expanding balloon?
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all other fragments move away, the farther away a fragment is the faster it moves away (remember drawing)
the universe is getting larger over time |
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Which interpretation is the correct one for our universe?
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The universe is getting larger over time
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Why do we believe that we live in an expanding universe?
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When the universe began it was tiny
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What does the big bang theory say about the beginning of the universe?
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It used to be tiny and very dense and extremely hot
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What does it say about the size, temperature and density soon after the beginning?
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As the universe expanded the matter spread out and cooled
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How does the big bang theory explain the existence of the 3 degree K microwave background radiation?
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38,000 years after the big bang the temp. was at 4,000 K, main radiation was visible light, electrons and protons combine to make hydrogen atoms, this made the universe transparent
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Why is the radiation we see today microwaves?
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It stretched 1,000 times
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The big bang theory predicts that only the lightest elements were created at the beginning of the universe. Why?
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the abundances of the lightest elements match the prediction of the big bang theory very well
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What are the "three pillars" of support for the standard big bang theory?
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Hubble Law, 3 degree K microwave background radiation and the abundance of light elements
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Is gravity only attractive?
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No, otherwise gravity should be slowing down the expansion of the universe
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How much the universe slows down depends on what?
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Density of matter in the universe
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What is meant by critical density?
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The density which just stops the expansion after an infinite time
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What are the three possible fates for the universe if the actual density is (1) less than, (2) equal to, or (3) greater than the critical density?
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Less than: keep expanding forever
Equal to: plateau eventually Greater than: collapse/end |
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If we just add up all of the matter that we see as galaxies, how does the density of matter compare to the critical density?
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Normal matter only (5%)
Normal matter and Dark Matter (30%) |
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Clusters of galaxies indicate that perhaps 90% of the matter in clusters is in some form other than visible galaxies. This is called what?
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Dark matter
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Recent studies of supernovas in very distant galaxies indicates that the rate of expansion of the universe is
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speeding up, not slowing down
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How would the size of the universe change over time if the rate of expansion is speeding up?
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Something in the universe has an anti-gravity effect
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Astronomers don't know yet exactly what causes this expansion, but it is hypothesized that there is ________ in the universe that makes gravity repulsive over very large distances.
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Dark energy
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What are the three possible shapes for the universe?
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Positive (globe), Zero (parallelogram), and negative (like a riding saddle)
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What shape is indicated by the microwave background radiation?
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Plane (zero/parallelogram)
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