1 / 28

Announcements

Announcements.

keilah
Download Presentation

Announcements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Announcements • Observing Night tonight. Weather does not look promising so have added three additional nights: Saturday, Monday and Tuesday. Forecast for Saturday is the best, Monday is OK (partly cloudy) and Tuesday is a chance of rain. We need to meet at the Farm around 6:15pm to start set-up.

  2. Measuring the Universe

  3. What parameters do we measure? H0: current value of the Hubble “constant” k: curvature parameter WM: mass/energy density parameter WDM: dark matter density parameter WL: cosmological constant parameter q0: deceleration parameter Determining these parameters will determine which model best fits the universe

  4. Measuring H0 Simple enough: measure the recessional velocity and distance to a bunch of galaxies and plot the data on a Hubble plot…the slope equals H0

  5. Measuring H is a little more complicated Shape factor and mass density affect H, especially when you get to large Z

  6. Another complication for H0: proper motion We are on a collision course with the Andromeda galaxy. Other galaxies have real motion with respect to us which may be comparable to the Hubble flow

  7. A major complication: how do you measure the distance? Determining the distance to the closest galaxies is relatively easy but the farther away it is, the more difficult it becomes

  8. What is needed are standard candles Cepheid variables can be seen from a large distance but after ~60 Mly they are no longer distinguishable from the background glow

  9. Type Ia supernovae make the best standard candle When a white dwarf star exceeds its mass limit (1.4MSun) it produces a Type Ia supernova which can be seen from billions of lightyears away

  10. Results from Type Ia Supernova observations

  11. Hubble Constant and the Age of the Universe

  12. Measuring the Shape Factor The sum of the angles around a triangle depends on the geometry but you have to measure really big triangles to see it (i.e. billions of lightyears on a side)

  13. We can get the shape factor from the CBR

  14. The angular size of the fluctuations gives us the shape Watch Geometry of the Universe WMAP video

  15. Measuring the Angular size of galaxies and other objects also shows the shape factor

  16. How much mass is there in the universe? And as a sub question

  17. Gravity Lensing is a means of measuring the mass in the universe

  18. Observing hot gas in galaxy clusters also measures mass Dynamical Methods rely on understanding the dynamics of galaxy clusters and the hot gas bound by them

  19. Galaxy rotation curves can give individual galaxy masses

  20. Big Bang Nucleosynthesis also puts constraints on the amount of baryonic matter Measuring the relative abundance of deuterium, lithium and helium-3 is one of the most difficult measurements to make requiring high precision spectroscopy

  21. The results indicate more dark matter than baryonic matter

  22. The next question is: Is it hot dark matter or cold dark matter?

  23. Measuring WL How do you measure something when you don’t even know what it is?

  24. For the most part WL is found by inference Observations of the CBR tell us the universe is flat (W = 1). Other observations tell us Wmatter≈ 0.3 so WL≈ 0.7

  25. The constituents of the universe according to Planck

  26. Observations of Large Scale Structure provides another independent method of finding WM

  27. Add all the observations together and the result is a universe that has a positive cosmological constant and is accelerating

  28. WMAP’s Summery of the cosmological quantities Watch Runaway Universe video

More Related