A brief but fairly up-to-date discussion of the basic observed properties of the isotropic ("monopole") and dipole features of the CMB.
The CMB discovery paper, which revolutionized cosmology and for which the authors received the 1978 Nobel Prize in Physics.
This is a brief but up-to-date and comprehensive summary of the CMB and the wealth of cosmological information it encodes; Smoot shared the 2006 Nobel Prize in Physics for his work on the CMB. He will visit Illinois this semester to give the Iben Lecture.
We will talk about the temperature fluctuations later in the course, so while you are welcome to read about these now, the main focus of the next week (and this Preflight) will be on the material in the first two pages.
A beautiful and still the best measurement of the CMB spectrum. Mather shared the 2006 Nobel Prize in Physics for his work on the CMB.
The questions are really meant to help guide your thinking as you read. You may find it helpful to look at the questions first and bear them in mind as you read.
Discussion Question 3
The Dark Sector of the Universe. Posted on Compass; your reply will be visible to your classmates.
The Cosmic Microwave Background: Discovery. Read the CMB discovery paper of Penzias & Wilson (1965). For those unfamiliar with radio astronomy, "antenna temperature" is in fact a unit for flux (really--intensity or surface brightness)--namely, the intensity that would result from a blackbody at the given temperature. Also note that they adopt a terminology (intimidating to theorists) which uses the phrase "atmospheric absorption" they refer to microwave emission from the (optically thin) thermal and non-thermal components of the atmosphere.
P&W report their discovery of an "excess antenna temperature" which they also call an excess "noise temperature." What do P&W mean by these terms--excess over what? What are important known sources of "noise" in their measurement? How big is the excess compared to the known noise?
What properties and/or quantities do they report the excess antenna temperature to have?
What interpretation do they offer for their result? What cosmological conclusions do they draw?
The Cosmic Microwave Background: Monopole. Although much information is encoded in the tiny CMB anisotropies, we first will understand and appreciate the important information in the large isotropic signal (the "monopole").
What are CMB observable(s) aside from the anisotropies?
What cosmological information do we learn from the observables of part (a)?
The Cosmic Microwave Background: Dipole.
What observationally is the CMB dipole? What is the relative size of the CMB dipole compared to the monopole?
What cosmological information do we learn from the dipole?
The CMB dipole measures a velocity; how is this velocity related (in magnitude and direction) to our orbital motion around the Milky Way? What are the implications of this result?
Consult the CMB spectrum in Figure 9.1 of Peacock and/or Figures 3, 4, and 5 from Fixen et al (2006). How close is the CMB to a Planck blackbody? Near the peak of the frequency spectrum, how tight are the limits on distroptions from a Planckian spectrum--i.e., what is the order of magnitude of the nonthermal-to-thermal intensity ratio Inontherm/Itherm? What information does this limit imply?
What are the Galactic foregrounds which add to the CMB to give the total signal from the microwave sky? What are strategies the COBE team used to remove these foregrounds?