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Exam

Exam. Final Exam: * Saturday Dec 14 th @ 9am University College Great Hall seats 1-49 * 2 hours Covers material starting with planetary system formation (refer back to previous sections). ~68 questions in 2 hours About a half dozen math questions

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Exam

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  1. Exam Final Exam: *Saturday Dec 14th @ 9am University College Great Hall seats 1-49* 2 hours Covers material starting with planetary system formation (refer back to previous sections). • ~68 questions in 2 hours • About a half dozen math questions • About a dozen B&W images – reminds you of colour images in ppt slides • Need to know equations: • Lifetime of star on MS • L, R, T • Hubble Law • Schwarzschild radius • Need to be able to do ratios of masses, timescales, convert units • Based on material from last test onward but includes previous material that is referred to in this section.

  2. Phys 1830: Lecture 34 • Previous Classes: • galaxies • interacting galaxies • This Class • cosmology

  3. Cosmology • Galaxies can be used to trace the structure and evolution of the universe. • The study of the structure and evolution of the universe as a whole is called cosmology.

  4. How galaxies trace the universe: • Measure the distance to galaxies: • Inverse Square Brightness Law: Use stars with known luminosity and measure their apparent brightness to get distance. • Cepheid Variable stars – the time period that they vary corresponds to their intrinsic luminosity. • Supernova Type Ia have a specific luminosity at the peak of their light curve.

  5. Distances to Stars Too Distant for Parallax Supernova Light Curve Light curve. • Recall we use variable stars and supernovae (Sne) to get distances to their host galaxies. • Blink images of galaxies to find SNe. • Compare the apparent brightness of the peak of the light curve with the intrinsic brightness of the peak to get distance via the Inverse Square Brightness Law.

  6. How galaxies trace the universe: • Measure the galaxies’ velocity: • Doppler Shift • Emission line gas (HII or HI) • Measure the distance to galaxies: • Inverse Square Brightness Law:

  7. How galaxies trace the universe: The most recent value: 74.3 +/- 2.1 km/s/Mpc • Hubble’s Law v = Ho * distance • Galaxies in general are are receding from us!  The universe is expanding.

  8. The Hubble distance-velocity relation states that a) mutual gravitational attraction of all objects in the universe means that all galaxies appear to be moving toward us, the closest ones traveling the fastest. b) all galaxies appear to have the same velocity away from us, irrespective of distance from us. c) the farther a galaxy is from us, the faster it appears to be moving away from us. d) all distant galaxies are moving toward us, the most distant galaxies fastest.

  9. How galaxies trace the universe: • Toy Universe with overheads. • Imagine winding the “film” of the expanding universe backwards, folding up the universe into a singularity. • The laws of physics break down  there is no time (classical) or time is poorly defined (Quantum Mechanics) .

  10. The Big Bang: • Jim Peebles – award winning Princeton cosmologist; undergraduate degree from University of Manitoba. • Following quotes are from Scientific American articles. • “That the universe is expanding and cooling is the essence of the big bang theory. You will notice I have said nothing about an "explosion"--the big bang theory describes how our universe is evolving, not how it began.”

  11. The Big Bang: Cosmologist Jim Peebles no centre  • It is somewhat misleading, however, to describe the expansion as some type of explosion of matter away from some particular point in space. • That is not the picture at all: in Einstein's universe the concept of space and the distribution of matter are intimately linked; the observed expansion of the system of galaxies reveals the unfolding of space itself. • An essential feature of the theory is that the average density in space declines as the universe expands; the distribution of matter forms no observable edge. not expanding into anything 

  12. The Cosmological Principle • We observe the universe to • look the same in every direction  ISOTROPIC • is the same everywhere • HOMOGENEOUS • This is inconsistent with an explosion. Large Scale Structure Cosmic Microwave Background Radiation

  13. The radiation of the Cosmic Microwave Background is known as “the surface of last scattering”. When viewing CMBR we are viewing only 300,000 years after the origin of the Universe! We look at distant objects, we look back in time. We can see the CMB in any direction in the sky. The Universe was very dense and very uniform at the surface of last scattering… how did structure (galaxies) get built up?

  14. The COBE satellite was the first instrument to map the fluctuations in the CMB and produced stunning results. Seeds of galaxy formation in the early universe. These fluctuations deviate from the black body curve intensity by only 1/10,000. CMB is an almost perfect blackbody at T=2.73 K, exactly as predicted by Big Bang cosmology! The “nail in the coffin” of Steady State Theory.

  15. Formation of Structure in the Universe as it Expands: WMAP of CMBR • Can use the fluctuations in the CMBR as initial conditions in cosmological simulations. • As the universe expands in the following simulation we zoom out. • As the universe stretches, galaxies that are close together simultaneously feel the gravitational pull on each other  Matches observations of Large Scale Structure

  16. Planck CMBR map

  17. Formation of Structure in the Universe as it Expands: 0.21 Gyr after Big Bang

  18. 1 Gyr after Big Bang

  19. ~5 Gyr after Big Bang

  20. 13.6 Gyr after Big Bang  now

  21. Large Scale Structure of the Universe (i.e. Cosmic Web)

  22. Clusters of Galaxies: Coma Cluster HST

  23. What is true about the expansion? • a) The average density in • space declines as the universe expands. • The distribution of matter forms no observable edge. • c) The distribution isotropic and has no centre. • d) The galaxies do NOT stretch as spacetime expands, but retain their extents. • e) All of the above.

  24. Big Bang: The Expansion of the Universe: Observations of SN Ia in 1998. The expansion is accelerating! • At large distances we are looking at the past. • For the same unit of distance, the change in velocity was smaller in the past than currently.  The speed of the expansion has increased with time.

  25. The Accelerating Universe Nobel Prize! • This is a huge shock for cosmology. There are a few explanations which are being investigated. • Some “force” seems to be counter-acting gravity to cause the galaxies to fly apart faster than expected. • This energy responsible for the acceleration is referred to as Dark Energy.

  26. The Accelerating Universe • Einstein’s cosmological constant may not have been such a big blunder after all – it can be used to describe the effect of Dark Energy. • Acceleration is sometimes seen as support for theorists’ preference for the “flat” curvature.

  27. Summary

  28. The Fate of the Universe: Expands Forever!

  29. Dark Matter and Dark Energy are the same thing: • True • False

  30. Discuss cosmology with your neighbour. What do you find the most intriguing or thing about it? Which is the most challenging concept for you? Are there any other cosmologies that you have heard about that you’d like to discuss?

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