Spring 2011

January 21, 2011
"The Glow of Galactic Antimatter" by Dr. Bethany R. Johns, '05, John Bahcall Public Policy Fellow, American Astronomical Society
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The structure of the Milky Way has been studied at many energies along the electromagnetic spectrum. At high energies, the Galactic 511 keV positron annihilation emission has a strong bulge component and a weak disk component. The bulge emission is about 1.4--6 times as bright as the disk emission. This high energy emission from the Galactic bulge has yet to be attributed to an astrophysical source of positrons. This research examines the morphology of the Galactic 511 keV positron annihilation emission by modeling Galactic positron production, propagation, and annihilation. Results show that the bulge emission cannot be explained by positron propagation from the disk to the bulge. The conclusion is that there must be a central positron production source or population of sources that produces positrons at low energy, such that they will be confined to and annihilate in the bulge region. Reception to follow.

January 28, 2011
"Black Holes and Gravitational Collapse" by David Garfinkle, Department of Physics, Oakland University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: In this talk, several topics are covered on gravitational collapse and the formation of black holes. These include cosmic censorship, critical gravitational collapse, and the nature of gravitational singularities. Physicists believe that the final stage of a massive enough object is a black hole, a region of spacetime where nothing - including light - can escape out. These black holes also have singularities, where spacetime curvature is infinite, therefore all laws of physics break down. To avoid this pathology, Roger Penrose in 1969 conjectured that all singularities formed inside black holes are hidden behind event horizons of black holes. This hypothesis, called cosmic censorship conjecture, is about formation and nature of singularities form in general relativity. After a brief explanation of the conjecture, I will describe what is known about gravitational collapse and general nature of singularities. Reception to follow.

February 4, 2011
"Barbie Bungee Jumping" by Society of Physics Students
3:00 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Join the Society of Physics Students for a riveting afternoon of Barbie Bungee Jumping....details to follow.

February 11, 2011
"Numerical Simulations of Coronal Processes" by Dr. Russell Dahlburg, Naval Research Laboratory
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Coming soon! Reception to follow.

February 18, 2011
"A Star in the Spotlight: Differential Rotation on II Pegasi" by Dr. Robert Harmon, Department of Physics and Astronomy, Ohio Wesleyan University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Starspots, like sunspots, are localized concentrations of magnetic field lines which suppress convection in the embedded plasma, choking off the flow of heat from below so that they become cooler and darker than the rest of the stellar surface. Stellar magnetic fields are generated by a dynamo process involving an interplay between convection and differential rotation, a latitude-dependence of the rotation rate made possible by the fact that a star is not a solid body. Here I present the results of a study of differential rotation on II Pegasi using starspots as tracers by mathematically inverting light curves obtained from 1987-2010 to produce indirect images of the star's surface. Reception to follow.

February 25, 2011
"Measuring Black Hole Masses using Reverberation Mapping" AND "OGLE-2008-BLG-513: Great Big Planet, Itty-Bitty Star"
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
This Physics Colloquium will feature talks by two astronomers from Ohio State University who will describe their doctoral research projects in observational astronomy/astrophysics: Kate Grier PhD candidate in Astronomy Ohio State University TITLE: "Measuring Black Hole Masses using Reverberation Mapping" ABSTRACT: I will discuss the methods of measuring the masses of black holes at the center of galaxies and how we use active galactic nuclei for this purpose. I will discuss the technique of reverberation mapping and show some preliminary results from the recent reverberation mapping campaign that we carried out last fall as a part of my thesis. Jennifer Yee PhD candidate in Astronomy Ohio State University TITLE: "OGLE-2008-BLG-513: Great Big Planet, Itty-Bitty Star" ABSTRACT: Gravitational microlensing can be used to find planets around other stars. I will present the microlensing event OGLE-2008-BLG-513 and use it to illustrate the microlensing technique for finding planets. The lens in this event consists of a massive giant planet orbiting a low-mass star and unlike in most microlensing events, the orbital motion of the planet can be measured. Reception to follow.

April 1, 2011
"Smelting" by Jonathan Edwards, '11 and "Stiff Strings and Other Things" by Benjamin Lucas, '11 - Senior Exercise Talks
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes 109)
Please join us for Jonathan Edward's and Benjamin Lucas' senior exercise talks. "Smelting" Abstract: To follow "Stiff Strings and Other Things" Abstract: The typical model used to study vibrating strings assumes that it is completely flexible. Real strings, however, have stiffness and this affects their vibrations. This talk will explore the effect that this has on a vibrating string and the sound that it produces. Reception to follow.

April 8, 2011
Senior Exercise Talks by Matthew Heimerdinger and Todd Skinner
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes 109)
Please join us for two exciting senior exercise talks. "Delayed Choice and Quantum Erasure: Shedding Light On a Quantum Puzzle" by Matthew Heimerdinger Many of the 'spooky' paradoxes of quantum mechanics are well known. In this talk, you'll find out about the delayed choice quantum eraser and how its counter-intuitive behavior highlights these phenomena and introduces a more unusual puzzle. and "The Physics of the Theremin" by Todd Skinner The Theremin is an early electronic musical instrument that was invented in the 1920s. Its signature eerie sound is commonly heard used in old science fiction movies and television shows, but it is also occasionally used in classical compositions. There is some fascinating physics that allows this instrument to function. In this talk, we will discuss the electronics and the basic properties that allows the Theremin to be played without touching it at all! Reception to follow.

April 15, 2011
"Cosmology with the South Pole Telescope" by Lindsey Bleem, Graduate Student, Kavli Institute for Cosmological Physics, University of Chicago
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The accelerating expansion of the universe poses some of the most puzzling questions in cosmology today. What is the 'Dark Energy' that is driving cosmological expansion? Is the explanation as simple as Einstein's cosmological constant or is there exotic new physics involved? To answer these questions we must first better characterize this phenomenon. The abundance of galaxy clusters is a powerful probe of the Dark Energy equation of state, since it depends upon both the expansion history of the universe and the growth of density fluctuations. I will describe recent results from the South Pole Telescope Survey, a project that was designed to probe Dark Energy through the detection of these massive systems. Reception to follow.

April 22, 2011
"Dark Energy: A Crisis in Fundamental Physics" by Dr. Christopher Stubbs, Professor of Physics and of Astronomy, Harvard University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Not only is the Universe expanding, but this is happening at an ever-increasing rate. The best explanation we have to date is that somehow empty regions of space experience a repulsive gravitational interaction, which is driving the accelerating cosmic expansion. The term "Dark Energy" is used to describe this phenomenon. I will describe some of the observational data that have forced cosmologists to accept this new reality, and will explain why it's so hard to understand in the current framework of physics. We are likely living through an intellectual revolution comparable to the advent of quantum mechanics, but it's unclear how long it will take for a deeper understanding to emerge. Reception to follow.

April 29, 2011
"Order and Chaos in the /. Body Problem" by John Lindner, Moore Professor of Astronomy, College of Wooster
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Increasing deep spaceflight activity and ongoing discoveries of extrasolar planets in unexpected orbits are some of the factors invigorating research in few body problems and celestial mechanics. In this talk, I describe the gravitational interaction of a massive line segment or slash (/) and a massive point or dot (.). Such a slashdot (/.) body problem is a simple but instructive prototype for the interplay between rotation and revolution, which characterize actual planets and natural satellites but not the interaction of idealized points. It is a semi-solvable model problem in the vicinity of the famous two and three body problems that anchor celestial mechanics. I demonstrate that it exhibits some of the richness of the three body problem with only two bodies. Applications include the dynamics of asteroid-moonlet pairs and asteroid rotation and escape rates. Reception to follow.

May 6, 2011
"An Anecdotal History of Physics at Kenyon College" by Thomas Greenslade, Professor Emeritus of Physics
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Physics has been taught at Kenyon since the College opened in Gambier in 1828. If you want the Straight Facts, click on the History link on the Physics Department home page. During this talk, I will add pictures to the Straight Facts and will chat about our academic ancestors and even some fairly recent people. Reception to follow.