Colloquium Archives

Warren Brown, Smithsonian Astrophyiscal Observatory

Topic: "Hypervelocity Stars"  (Video)

Abstract: A massive black hole sits in the heart of the Milky Way. Most stars are found in multiple systems. A consequence of these two facts are "hypervelocity stars" ejected from the Milky Way at million mph velocities. I discovered the first hypervelocity star in 2005, and since then have found more than 20 unbound hypervelocity stars in a targeted survey. Recent results include new evidence for their origin, an unexplained spatial distribution on the sky, and Hubble Space Telescope proper motion measurements that may allow us constrain the shape and orientation of the Galactic potential.

David Lowe, Brown University

Topic: "Journeys Through Black Holes with Schrodinger's Cat"  (Video)

Abstract: We explore some of the properties of black holes and the evidence for their existence. Many puzzles arise when the laws of quantum mechanics are applied to black holes, which are only to be resolved by invoking new physics. Some of the competing hypotheses are described.

Gurtina Besla, Columbia University

Topic: "Galaxy Collisions in Our Local Neighborhood"  (Video)

Abstract: Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. With the first direct proper motion measurement of M31, its future collision with the Milky Way is the most imminent major cosmic event effecting our solar system that can be predicted with some certainty. New proper motions of the Milky Way's largest satellite galaxies, the Large and Small Magellanic Clouds (LMC and SMC), have overturned the canonical picture in which the Clouds have made multiple orbits about the Milky Way, suggesting instead that they may be recent interlopers to our system. Models of the LMC/SMC system also suggests that they have recently collided in a dramatic event that formed a star forming bridge of gas connecting these two dwarf galaxies. These studies illustrate that we need only look to our local neighborhood to find galaxies in the midst of violent encounters.

Lance Labun, National Taiwan University

Topic: "Probing the quantum vacuum with high intensity lasers"  (Video)

Abstract: A long-standing prediction of relativistic quantum theory is that a potential step greater than twice the particle mass, Delta V>2m, spontaneously emits charged particles. The same is true of gauge potentials, such as the electromagnetic field: When the electric field strength nears a critical magnitude determined by the electron mass, field energy is rapidly converted into electron-positron pairs. In other words, the usual zero-particle perturbative vacuum state decays into what is expected to be a hot plasma of electrons, positrons and photons. This effect may soon be achievable in the lab by focusing and compressing high energy laser pulses. I will discuss how exploring pair production and vacuum decay in lab experiments in the context of quantum electrodynamics will provide a new tool to understand particle production and entropy generation in relativistic hadron collisions and confinement of color charge (why there are no free quarks), and may offer insights into Hawking radiation.

Stuart Solin, Washington University

Topic: "Extraordinary Physics in Semiconductor-Metal Hybrid Structures"  (Video)

Abstract: “EXX” phenomena in macroscopic, microscopic and nanoscopic metal-semiconductor hybrid structures will be described. Here E = extraordinary and XX = magnetoresistance (EMR), [1,2] piezoconductance (EPC), [3] optoconductance (EOC), [4] and electroconductance (EEC). [5] The underlying phyiscs of EXX phenomena will be elucidated with particular emphasis on both analytic and finite element analysis methods to quantitatively account for the observed EXX enhancement. Surprising new aspects of the mesoscopic physics of the nano-hybrid structures will be addressed including the recently discovered inverse-EOC or I-EOC.[6] So to will new 3-dimensional EMR phenomena.[7] Time permitting, it will also be shown how EXX nanosensors can be employed for several applications ranging from ultra high density magnetic recording to the study of the properties of cancer cells with ultra-high spatial resolution.

Ian Spielman, NIST

Topic: "Gauge Fields With Cold Atoms"  (Video)

Abstract: Gauge fields are ubiquitous in Physics. For example, in the context of high energy physics, they are the fundamental carrier of forces; while in condensed matter systems the associated physical fields (electrical and magnetic) are essential in creating and understanding many-body phenomena.

Here I present our experimental work synthesizing static gauge fields for ultracold neutral atoms -- analogous to applied fields in condensed matter systems -- and I will discuss these static gauge fields both in terms of conventional electromagnetism and also using the language of spin-orbit coupling.