Seminars are held at 4:00 PM on Tuesdays in Room F160
on the first floor of the Technological Institute (2145 Sheridan Road) unless otherwise noted
Fall Quarter 2014
Date  Speaker / Seminar  Host  
Sept. 23  Mike McCourt The hot plasma filling galaxy clusters is susceptible to a convective MHD instability known as the MTI. Understanding the implications of this convection has been surprisingly difficult, however; it depends on both the largescale evolution of the cluster and on the plasma physics of the gas. I will describe a new set of "semicosmological" simulations which capture enough of the cosmic evolution of galaxy clusters to reproduce their largescale properties but still provide an idealized environment in which to study cluster convection and its implications. I will also describe some future applications of these simulations to other problems in galaxy formation. 
ClaudeAndré FaucherGiguère 

Sept. 30  Francesca Valsecchi Two formation models have been proposed to explain hot Jupiters’ tight orbits. These could have migrated inward in a disk (disk migration), or they could have formed via tidal circularization of an orbit made highly eccentric following gravitational interactions with a companion (higheccentricity migration). Disk migration drives hot Jupiters down to their Roche limit separations a_R, in orbits where the stellar spin and orbital angular momentum vectors are nearly aligned. Higheccentricity migration results in an inner cutoff at 2a_R and in a broad range of misalignments. Using stateoftheart stellar models and a detailed treatment of tidal dissipation, we show that currently observed systems are consistent with higheccentricity migration. In this scenario, stellar tides shaped the observed distribution of misalignments, and brought inward from beyond 2a_R the currently known hot Jupiters that lie within 2a_R. Interestingly, this population potentially provides direct empirical constraints on tidal dissipation theories. 


Oct. 7  Andrew MacFadyen Gammarays bursts and their afterglows involve the dynamics of highly relativistic plasma as it is accelerated at the central engine and expands over more than ten orders of magnitude in length scale. I will discuss high resolution studies of GRB jets using a powerful new code (JET) which employs a moving numerical mesh, thus allowing for highly accurate Lagrangian multidimensional simulations of relativistic jet dynamics. I will present the first multidimensional simulations of a collapsar jet starting from the center of a massive star, breaking out of the stellar surface, coasting and producing internal then external shocks. Synchrotron light curves computed from the simulation data naturally produce the early steep decay and extended plateau observed in early Xray light curves. During the deceleration phase I will demonstrate that GRB jets are unstable to the RayleighTaylor instability. This makes the jets turbulent, thus amplifying magnetic fields via smallscale dynamo to values sufficient to explain the synchrotron emission. The RayleighTaylor fingers can also impact the forward shock thus corrugating it with possible implications for the afterglow emission. I will demonstrate fits of theoretical light curves computed from numerical simulations to the observational data. 
Shane Larson 

Oct. 14  Ryan Foley 
Vicky Kalogera 

Oct. 21  Rachel Friesen 
Laura Fissel 

Nov. 4  Gwen Rudie 
ClaudeAndré FaucherGiguère 

Nov. 11  Saul Rappaport 
Fred Rasio and Francesca Valsecchi 

Nov. 25  Edwin Bergin 
Farhad Zadeh 
Winter Quarter 2015
Date  Speaker / Seminar  Host  
Jan. 13  Michael Meyer 
Fred Rasio 

Jan. 27  Tom Abel Computational Physics allows us to study extremely nonlinear systems with fidelity. In astrophysical hydrodynamics and studies of galaxy formation much of the last two decades we have explored various discretization techniques and found subtle differences in some applications. Interestingly numerical studies of collisionless fluids such as e.g. the collapse of cold dark matter to form the large scale structure of the Universe has only been studied meaningfully with one approach; Nbody Monte Carlo techniques. I will introduce a novel simulation approach, and demonstrate its feasibility, that for the first time can study a collisionless system in the continuum limit in multidimensions. I will also show this new technique opens a new window in making sense of structure formation as well as plasma physics. In this context we have developed a novel rasterization/voxelization algorithm applicable in computational geometry, computational physics, CAD design and other fields. I show how these approaches allow also for much improved predictions for gravitational lensing, dark matter annihilation, properties of cosmic velocity fields , and many other applications. 
Fred Rasio 
For more information, contact:
Janet Howe (janet.howe@northwestern.edu)
Past Astrophysics Seminars