IDEAS IN ASTROPHYSICS

UMBC Astrophysics Journal Club, Fall 2006

Meeting, time and place: Monday 14:30-15:30 in PHYS 221

Contact Info: Dr. Markos Georganopoulos E-mail: georgano@umbc.edu,
UMBC Office: 1-410-455-8149. Tuesday afternoons try my NASA/GSFC office: 1-301-286-0993


Bullet cluster of galaxies
From Science, Aug 25, 2006: Normal matter (pink) and gravity (blue) show dark matter's presence in the bullet cluster of galaxies. CREDITS: NASA/CXC/CFA/M. MARKEVITCH ET AL.

Summary

We will go through some interesting and important ideas in astrophysics. Every student will research and present one or two topics (one for physics grads and incoming astronomy grads, two for more advanced astronomy grads). You will be given a "starting point", usually a chapter from a textbook dealing with the issue and/or the original article(s) that initiated the topic. You are expected to present the topic as a lecture to the rest of the group. You should spend ~ 2/3 of the 40 min lecture presenting, in a pedagogical manner, the basic idea, and use the remaining time discussing the evolution and applications of the idea up to now. No previous astronomy knowledge is required.

Topics/Schedule

September 18 Back of the envelope GPS relativistic corrections.
Both special and general relativistic corrections are required for the GPS system to work properly. Because the earth's gravity field is weak, one can get away with doing the calculation in the weak field limit, using the equivalence priciple.
Presenter: Hao You.
Bibliography: Chapter 6 of James Hartle's Introduction to General Relativity.
September 25 When matter dethroned radiation.
The equations for describing the evolution of the Universe can be derived in a Newtonian manner. Solving them, we can see when the energy density of matter became greater than that of radiation.
Presenter: Jianning Zeng
Bibliography: Chapters 4-6 of Barbara Ryden's Introduction to Cosmology. Enjoy also, Friedmann's original 1992 paper (translated in English) on the famous Friedmann's equation, that Einstein thought to only be a mathematical curiosity.
October 2 Nucleosynthesis in the era of radiation.
Sometime during the early stages of the radiation era, the light elements were formed. The calculated abundances are one of the most stringent tests that the big bang theory passed with flying colors.
Presenter: Sarah Bank
Bibliography: Chapter 10 of Barbara Ryden's Introduction to Cosmology.
October 9 No meeting this time
October 16 When matter and radiation stopped talking.
As the Universe kept expanding, photons decoupled from matter and radiation evolved separately. This is the cosmic microwave background (CMB) that gave Penzias and Wilson the Nobel price. One can follow this unique part of our Universe's history with relatively simple calculations.
Presenter: Katayoon Saadin
Bibliography: Chapter 9 of Barbara Ryden's Introduction to Cosmology.
October 23 The adventures of light in special relativity.
Special relativistic effects give a range of interesting phenomena like apparent superluminal motions and Doppler boosting that been observed in quasar jets. The calculations are a good exercise in special relativity.
Presenter: Alex Padgett
Bibliography: Chapter 4 or Rybicki & Lightman Radiative proceses in Astrophysics.
October 30 What killed the highest energy cosmic rays?
Try to propagate high energy particles through the fog of the CMB. Greisen-Zatsepin-Kuz'min (GKZ) realized back in the sixties that you cannot do that if your particles have energies greater than ~ 10^20 eV. To get to this we will first review four vectors.
Presenter: Jianning Zeng
Bibliography: Chapter 5 or Hartle's Gravity: an Introduction to Einstein's Realtivity. Take a look also at a very recent observation of the GKZ cutoff in astro-ph/0609403
November 6 Why are big black holes inner-city dwellers in every galactopolis?
Dynamic friction, discussed by Chandrasekhar back in the 30's, will slow down a star propagating through a collection of other stars. The phenomenon, called dynamic friction, can be described with a formalism similar to that used for calculating ionization losses, and is responsible for supermassive black holes occupying the prime real estate of most galaxies.
Presenter: Brian Wingert
November 13 Destination black hole: where is the last "kiss and ride" stop?
We tend to thing that the Schwarzschild radius Rs is the closest we can get to a black hole without being sucked in for good. It turns out that the closest you can get is 6 Rs and the calculation is a good introduction to dealing with orbits in the Schwarzschild metric.
Presenter: Brian Wingert
November 20 1937, the first business card dark matter is picked up by an earthling.
It took a character like Zwicky, to realize that the high velocity of galaxies in clusters is an indication that dark matter exists. Zwicky also suggested that gravitational lensing of background objects can be used to measure dark matter. Recent accurate techniques, co-developed by one of our own, make use of the cluster X-ray emission to weigh its dark matter.
Presenter: Deatrick Foster
December 4 Electrons bullying cosmic microwave background photons
Sunyaev and Zeldovich showed in 1969 that when a CMB photon passes through a galaxy cluster, its energy increases by ~ 0.05% due to Compton scattering of energetic electrons. This phenomenon has been observed and provides an independent way of measuring the clusters mass.
Presenter: Deatrick Foster
December 11 How to make electrons with the energy of a ping-pong ball.
Fermi first introduced the idea of accelerating electrons by repeated collisions with magnetic field irregularities. Here we will discuss how this mechanism works, together with another, more efficient variant that takes place at shock waves.
Presenter: Alex Padgett