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Homework for today was WORKBOOK EXERCISE: “ Expansion of the Universe ” (pg. 87-88 in workbook)

Homework for today was WORKBOOK EXERCISE: “ Expansion of the Universe ” (pg. 87-88 in workbook). Mapping the Universe. Chapter 16. The Local Group. The Local Group group of galaxies Milky Way is member at least 30 galaxies 3 large spirals Milky Way, Andromeda, M33

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Homework for today was WORKBOOK EXERCISE: “ Expansion of the Universe ” (pg. 87-88 in workbook)

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  1. Homework for today was • WORKBOOK EXERCISE: • “Expansion of the Universe” • (pg. 87-88 in workbook)

  2. Mapping the Universe Chapter 16

  3. The Local Group • The Local Group • group of galaxies • Milky Way is member • at least 30 galaxies • 3 large spirals • Milky Way, Andromeda, M33 • remainder mostly dwarf ellipticals

  4. Galaxy Clusters • Most galaxies found in “galaxy clusters” • Examples: Virgo cluster, Coma cluster • Superclusters • extremely richgalaxy clusters

  5. Structure in the Universe • Galaxy surveys show structure • voids • filaments/sheets • Galaxy clusters • found within the filaments/sheets • Superclusters • found at intersections of several filaments/sheets

  6. Evolution of Galaxies • Galaxy formation • Universe ~14 billion years old • star formation more active in past • Galaxies change, as a result of: • star formation • stellar evolution • galaxy collisions & cannibalism

  7. Dark Matter • Mass of Galaxy Clusters • determined by galaxy orbital motion • M/L ~ 300 • Universe is 99% dark matter

  8. The Big Bang Chapter 17

  9. Cosmological Principle • Cosmological principle • on large scales, Universe is: • isotropic • looks the same in all directions • homogeneous • any region of space is about the same as any other

  10. Age of the Universe • Hubble: Universe is expanding • “Run movie backward” • at beginning • all matter within small region (single point) • very, very hot • Subsequent expansion • called Big Bang • not an explosion • galaxies not moving (flying apart) • space is expanding • Age of the Universe To = 1/H (Hubble time) ~ 14 billion years

  11. Big Bang Model • Early universe very hot, very dense (mostly radiation) • As it expanded, it cooled • Eventually, atomic nuclei form • when universe about 3 minutes old • only simple atoms (hydrogen [deuterium], helium, lithium) • Later, matter becomes transparent • light escapes • produces continuous spectrum (blackbody) • cosmic microwave background radiation (CMB) • Much later, stars and galaxies form

  12. Evidence for the Big Bang • Expanding universe • Cosmic Background Radiation • discovered by Penzias & Wilson in 1960’s (won Nobel Prize 1978) • light released when matter became transparent • Observed background matches predicted temperature (3 K) • Nucleosynthesis • Model predicts Universe is 75% hydrogen, 25% helium. • Matches observed abundances • Details provide strong evidence

  13. Fate of the Universe • Big Bang: 3 possible fates • depends on mass (=gravity) of Universe • open universe (the Big Chill) • not enough mass to stop the expansion • universe expands forever • flat universe • exactly enough mass to stop the expansion, but in infinite time • closed universe (the Big Crunch) • enough mass to stop expansion • followed by contraction back to single point • Latest results (Supernova Cosmology) • Indicate that the Universe is ACCELERATING!

  14. Current Status • Careful tests via CMB observations • Universe is flat • 4% normal matter • 0.3% is luminous • 23% dark, exotic matter • what is it? • 73% dark energy • produces anti-gravity • expansion rate is increasing • what is it?

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