lecture23_08 - Lecture 23 Measuring Galaxies Hubble Law The...

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Lecture 23 Measuring Galaxies Hubble Law The Expanding Universe Basic Cosmology
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Tutorial/Help sessions : Thurs. 6 th , Thurs. 11 th , Mon.15 th all in Koffler KP108, 4-5pm.
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Measuring Galaxies 1. Most important properties of a galaxy that we can measure are its distance, mass, and motion.
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Distances Measured by Various Indicators 1. Cepheid variables are excellent distance indicators but can be seen in only relatively nearby galaxies, out to perhaps 200 million light-years. 2. Bright stars (giants, supergiants, novae) can also be used as distance indicators. 3. Large globular clusters and supernovae are of consistent brightness so they, too, can be used to determine distances to more distant galaxies.
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Distances Measured by Various Indicators (cont.) 4. These objects allow astronomers to determine distances out to about 1000 million light-years. 5. Starting with the period-luminosity relationship of Cepheids , astronomers are able to follow a chain of reasoning and observation that allows them to determine the distances to galaxies too far away for their Cepheids to be visible.
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Fig. 17-9 m - M = 5 log d - 5 Other things (e.g. galaxies, supernovae) Cepheids
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The Hubble Law 1. In 1912, Slipher found that spiral nebulae had redshifted spectra indicating that they were moving away from us at tremendous velocity. 2. In 1920s, Hubble and Humason showed that there is a relationship between the recessional velocities of galaxies and their distances. 3. Hubble showed that the universe is expanding, and his work is the foundation for today’s theories of cosmology —the study of the nature and evolution of the universe as a whole.
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Original Hubble & Humason data (1920's)
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The Hubble Law (cont.) 4. The redshift that Hubble observed is not due to the Doppler effect in the simple sense, but can be interpreted that way. (Expansion of space, not motion through it). 5. The Hubble law states that a galaxy’s recessional speed ( υ ) is directly proportional to its distance ( d ): υ = H 0 d , where H 0 is the Hubble constant (the proportionality constant in the Hubble law; the ratio of recessional velocities of galaxies to their distances).
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Hubble Law to redshift z=0.1 More detail on next slide
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6. Modern day measurements of the Hubble constant place it between 15 and 25 km/s per million light- years (MLY) or between 50 and 80 km/s per megaparsec (Mpc). The Hubble Space Telescope Key Project, led by Wendy Freedman, and other projects, have converged on H 0 ~ 71 +/- 7 km/s/Mpc. 7. The latest observations of the radiation left over from the hot big bang indicate a value of H 0 = 71 ± 4 km/(s × Mpc) or about 21.8 km/(s × MLY). We call this the “Concordance Model”. Furthermore,
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This note was uploaded on 04/22/2009 for the course AST 210 taught by Professor Prof.stefanmochnacki during the Fall '08 term at University of Toronto- Toronto.

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lecture23_08 - Lecture 23 Measuring Galaxies Hubble Law The...

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