Astr 5460     Fri., Jan. 24, 2003
   Today: Cinnamon Internet/Projection Test
              Ordering Textbook
Course Webpage
Astro-ph (xxx.lanl.gov)
Longair, Chapter 1 (History)
Assignment for next Friday
 Note: This class will meet W&F, 5440 will be M&W

“Astro-ph”
The Los Alamos Preprint Server for physics and astronomy at http://xxx.lanl.gov
Standing assignment: review the abstracts daily
Probably once a week (Fridays) we’ll discuss the exgal papers that seem the most interesting
Not a big deal here – just trying to establish good habits

Course Webpage
Start from my webpage:
http://physics.uwyo.edu/~mbrother
Hit the ASTR 5460 Link
Not much there now, but that will be the clearinghouse for course information, including lecture slides, links to articles, assignments, etc.

Prehistory
Edwin Hubble
Distances to the “Spiral Nebula” using Cepheids:

Prehistory
Edwin Hubble
Distances to the “Spiral Nebula” using Cepheids
Hubble Law:

The Hubble Law using galaxies with visible Cepheid variables.

The Hubble Law and the Age of the Universe
Ho = 72 ±8 km/s/Mpc

Assignment for next Friday
Recreate Hubble’s 1929 plot using the same galaxies he used, but use modern values.
You will probably need to use NED (NASA Extragalactic Database) and/or NASA’s ADS abstract service to find these values.
Make a nice plot using the plotting package of your choice (e.g., IDL, sm, igi, by hand).
Get the slope (method of your choice, some are better than others) which is the Hubble constant.
Compare your value to Hubble’s and to the modern value.  What’s going on?
You might want to learn to use LaTeX, too.

Theory of Expanding Universe
Einstein (1915) and General Relativity, in 1917 uses the cosmological constant to get a static universe solution (“Greatest blunder of my career.”)
de Sitter, Friedman, and Lemaitre follow, with more solutions covering a variety of situations, including no matter, closed universes, and expanding universes (and this is all before Hubble found and expanding universe)
Cosmological constant was handy, however, for reconciling Hubble’s universe age with the age of Earth, and handy today in reconciling otherwise conflicting data.

The Big Bang
George Gamow (late 1940s) realized that running the expansion backwards means a hot, dense early universe that was radiation dominated, and nucleosynthesis was possible.
With Alpher and Herman predicted background radiation left over from this period, which would now have a temperature of about 5 K.
Penzias and Wilson discover the background radiation in 1965 by accident, win Nobel prize.

Prediction from Big Bang Model:
Abundance of the light elements
Big Bang Nucleosynthesis
T, r both high enough at start to fuse protons into heavier elements
T, r  both dropping quickly so only have time enough to fuse a certain amount.
Simple models of expansion predict 24% abundance He
24% is the amount of He observed*
Abundance of 2H, 3He, 7Li depends on rnormal matter
Suggests rnormal matter is only 5% of rcritical
But we need to also consider “dark matter” and its gravity

Prediction from Big Bang model:
Cosmic Background Radiation
Look out (and back in time) to place  where H became neutral
Beyond that the high density ionized H forms an opaque “wall”
Originally ~3000 K blackbody radiation
The material that emitted it was moving away from us at extreme speed
That v produces extreme redshift (z=1000), so photons all appear much redder, so T appears cooler
With red shift, get 2.7 K Planck blackbody
Should be same in all directions

Cosmic Microwave Background Observations
First detected by Wilson and Penzias in 1960’s
Serendipitous detection – thought is was noise in their radio telescope but couldn’t find cause.  Only later heard of theoretical predictions
Best spectrum observed by COBE satellite
Red curve is theoretical prediction
43 Observed data points plotted there
error bars so small they are covered by curve.
it is covered by curve.
Isotropy also measured by COBE
T varies by less than 0.01 K across sky
Small “dipole” anisotropy seen
Blue = 2.721    Red = 2.729
Caused by motion of Milky Way falling towards the Virgo supercluster.

Critical points with time running forward
10-45 sec Quantum gravity?  Physics not understood
10-34 sec 1026 K Nuclear strong force/electro weak force separate
(inflation, matter/antimatter asymmetry)
  10-7 sec 1014 K Protons, AntiprotonsÛphotons
  10-4 sec 1012 K Number of protons frozen
    4   sec            1010 K                  Number of electrons frozen
    2   min Deuterium nuclei begins to survive
    3   min 109  K Helium nuclei begin to survive
  30   min           108  K                     T, r too low for more nuclear reactions
(frozen number of D, He -- critical prediction)
300,000 yr 104  K Neutral H atoms begin to survive
(frozen number of photons – critical prediction)
 1 billion yr Galaxies begin to form
13 billion yr Present time

Big Bang Essentials
Hubble Expansion
Black Body Background Radiation
Light Element Abundances
Age of oldest stars consistent with Ho age

Galaxy Formation
Lots of theory here!
Jeans (1902), gravitational collapse in a stationary medium, depends on sound speed and density
Lifshitz (1946), general case including expanding medium, but collapse is not typically exponetial and structures grow very slowly – too slowly! Cannot start with infinitesimal perturbations.
Zeldovich, Novikov, Peebles (1960s) used finite perturbations (1 part in 10000).
Main test of all this is the cosmic microwave background radiation, since fluctations should leave imprints.

Galaxy Formation
Thermal history of pregalactic gas can be worked out in detail (and we will do so!).
Density fluctuations tied to temperature fluctuations, revealed finally by COBE, but small.  Lots more details to go into here later in course.
Two main ideas: top-down vs. bottom-up.
Need for dark matter (hot or cold) became apparent – normal matter needs help to collapse into galaxies.

Very Early Universe
Isotropy – the universe looks the same in all directions, again strictly true on large scales
Small Baryon/Anti-baryon asymmetry
Close to critical (Omega = 1) (will be HW)
Initial fluctuations to seed structure growth

Very Early Universe
Inflation (Guth, others, early 1980s) resolves some of these properties.  Inflation posits an early exponential expansion of the universe that leaves the curvature flat (close to omega = 1) and takes regions in causal contact and moves them far beyond their local horizons (isotropy).  May help form the fluctuations leading to galaxies.