Theory Group Meetings 2015-2016
Theory Group Meetings are held at 12:30 PM in Tech F160 (2145 Sheridan Rd) unless otherwise noted Theory Group Meeting is the informal weekly discussion group of theoretical astrophysicists at CIERA. Discussions usually center around blackboard talks given by graduate students and postdocs at Northwestern, but can include prepared talks given external speakers, as well. Whatever slides or material the speaker brings in, Theory Group Meeting often becomes a quite detailed discussion of the fundamental theoretical astrophysics topic being addressed. Also, while topics under discussion often relate to theory, observational astrophysicists are definitely welcome!
Spring Quarter 2016
Date |
Speaker / Seminar |
Apr. 8 |
Daniel Angles-Alcazar
The Baryon Cycle in Galaxy Evolution
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Michael Katz
Study of Near-Band Edge Sources for the LISA Detector
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Brandon Miller
Using Single-spin Templates for GW Parameter Estimation
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Apr. 15 |
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Cliff Johnson
University of California - San Diego
Insights on Star Cluster Formation from M31
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Laura Fissel
The Role of Magnetic Fields in Star Formation
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Apr. 22 |
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Mads Sørenson
Geneva Observatory of the University of Geneva
The Evolution of Black Hole X-ray Binaries
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Sourav Chatterjee
Dynamical Effects of Black Holes on Star Clusters
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Apr. 29 |
Jason Hwang
Creating Kepler-36 Through a Hit and Run
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Michael Zevin
Machine Learning Applications in LIGO Detector Characterization and Binary Evolution
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May 13 |
Fabio Antonini
Slow Mass Segregation and the Distribution of Stellar Remnants at the Galactic Center
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Fani Dosopoulou
Dynamical Friction in Eccentric Massive Black Hole Binaries
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May 20 |
Ben Nelson
Push it to the (Roche) Limit: Inferring Multiple Populations of Hot Jupiters
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Katie Breivik
Distinguishing Binary Black Hole Formation Channels with (e)LISA
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May 27 |
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Jeff Andrews
Crete Astrophysics Group, Greece
Beyond Population Synthesis: Markov-Chain Monte Carlo Models of High Mass X-ray Binaries
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Niharika Sravan
Massive Star Winds and Implications for Binary Evolution
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Winter Quarter 2016
Date |
Speaker / Seminar |
Jan. 15 |
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Michael Tremmel
University of Wisconsin
A New Hope: Improving on Formation, Dynamics and Accretion Models of SMBHs in Cosmological Simulations
Supermassive black hole physics is a crucial aspect of galaxy evolution theory, but modeling their dynamics and accretion also present a unique challenge for large-scale cosmological simulations. I present a new, physically motivated sub-grid model for SMBH formation, dynamics, and accretion in large-scale cosmological simulations that better accounts for the local (resolved) environment . I will highlight how each aspect of our approach leads to testable outcomes compared to common SMBHs prescriptions. Finally, I will present a first application of this scheme studying the properties and time evolution of dual, active SMBHs. |
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Jan. 22 |
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Betsy Mills
NRAO
Do star formation laws break in the center of the Galaxy?
I will review our understanding of molecular gas conditions in the central 500 parsecs of the Milky Way, and summarize recent studies that find that the Galactic center deviates from universal star formation relations. It is suggested that the amount of star formation in the Galactic center is less than expected, given the quantity of dense gas in this region. However, in order to conclude that the Galactic center truly breaks these laws' of star formation, two possibilities must be ruled out: that our indicators in this region could underestimate the amount of star formation, and that prior observations could have overestimated the amount of dense gas. I will analyze new evidence for ongoing star formation in the Galactic center and present new measurements of the gas densities in the Galactic center that show it to be less dense than originally thought. However, I will ultimately argue that the average density of the gas is less relevant to explaining the dearth of star formation than the fraction of gas at each density. |
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Jan. 29 |
Alex Richings Non-equilibrium Chemistry in Simulations of Galaxy Formation
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Feb. 5 |
Sam Hadden Tutorial on REBOUND, an Nbody
program
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Feb. 19 |
Chris Pankow Implications from the discovery of GW150914, a heavy binary black hole binary
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Feb. 26 |
Laura Sampson
Testing General Relativity with GW150914
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Mar. 11 |
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Manos Chatzopoulos
University of Chicago
A Decade of Super-Luminous Supernova Discoveries: The Physics of Extreme Stellar Catastrophes |
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Fall Quarter 2015
Date |
Speaker / Seminar |
Oct. 9 |
Laura Sampson
Astrophysical Inference with Pulsar Timing Arrays
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Jason Hwang
SPH Simulations of Planet—Planet Collisions |
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Oct. 16 |
Chris Pankow Bayesian Parameter Estimation for Binary Neutron Stars in the Advanced LIGO Era |
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Oct. 23 |
Ben Nelson
Statistical and Dynamical Remastering of Classic Exoplanet Systems |
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Oct. 30 |
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Blake Sherwin
UC Berkeley
Mapping Mass Across the Universe: CMB Lensing Measurements Past and Future
Measurements of gravitational lensing in the CMB directly probe the projected distribution of mass out to high redshifts, and thus encode a wealth of information about cosmology. In my talk, I will explain how CMB lensing measurements will allow us to precisely determine the masses of neutrinos, probe the relation between dark and luminous matter at high redshifts, and constrain the properties of inflation and the early universe. After reviewing first measurements of CMB lensing, I will discuss new studies of the lensing effect with CMB data from the ACTPol experiment. I will show the remarkable precision achievable by CMB lensing surveys over just the next five years and explain the great scientific returns and challenges we can expect from these surveys. |
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Nov. 6 |
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John Chisholm
UW Madison
Shining a Light on Star Formation Driven Outflows: the Physical Conditions within Galactic Outflows
Stellar feedback drives energy and momentum into the surrounding gas, which drives gas and metals out of galaxies through a galactic outflow. Unfortunately, galactic outflows are difficult to observe and characterize because they are extremely diffuse, and contain gas at many different temperatures. Here we present results from a sample of 37 nearby (z < 0.27) star forming galaxies observed in the ultraviolet with the Cosmic Origins Spectrograph on the Hubble Space Telescope. The sample covers over three decades in stellar mass and star formation rate, probing different morphologies such as dwarf irregulars and high-mass merging systems. Using four different UV absorption lines (O I, Si II, Si III and Si IV) that trace a wide range of temperatures (ionization potentials between 13.6eV and 45eV), we find shallow correlations between the outflow velocity or the equivalent width of absorption lines with stellar mass or star formation rate. Absorption lines probing different temperature phases have similar centroid velocities and line widths, indicating that they are comoving. Using the equivalent width ratios of the four different transitions, we find the ratios to be consistent with photo-ionized outflows, with moderately strong ionization parameters. By constraining the ionization mechanism we model the ionization fractions for each transition, but find the ionization fractions depend crucially on input model parameters. |
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Daniel Angles-Alcazar
Tracing Cosmic Inflows, Galactic Outflows, and Gas Recycling in Realistic Environments
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Nov. 13 |
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Greg Sloan
Cornell
Carbon-rich Interstellar Dust from Fullerenes to Aliphatics |
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Josh Fixelle
Resolving the Complexities of Hot Jupiter Mass Transfer via Roche Lobe Overflow
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Nov. 20
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Shuo Zhang
Columbia
Hard X-ray Outburst History of Sgr A*
The Galactic center supermassive black hole (SMBH) Sagittarius A* (Sgr A*)
is remarkably underluminous with a bolometric luminosity about 10^-9 times
its Eddington luminosity. It is the closest SMBH and thus an ideal target
for investigation of galactic nuclei and their activity cycles. This goal
can be fulfilled by studying its past, current and possible future
outbursts. Its current X-ray quiescent state, with a luminosity of Lx ~
10^33 erg/s, is punctuated by flares up to a few times 10^35 erg/s, whose
origin is poorly understood. I collected nine hard X-ray flares detected
up to 79 keV, and studied their timing behavior using the Bayesian block
analysis. The broadband 3-79 keV spectroscopic studies show that the X-ray
flares can have a range of photon indexes, which can be explained by the
magnetic reconnection scenario. During the flares, Sgr A* is still orders
of magnitudes lower than its Eddington luminosity. Whether it has ever
experienced more substantial increases in activity as observed in
low-luminosity Active Galactic Nuclei is still under discussion.
Indication of such past activity of Sgr A* has come from the Galactic
center molecular clouds (GCMCs). I use the hard X-ray emission from GCMCs to constrain the past Sgr A* X-ray outburst, resulting in Lx~5x10^38 erg/s with a photon index of ~2.2. I also discovered different timing
variability from different cloud substructures, which can further
constrain the past outburst. Future Sgr A* flaring activity could be
affected by the G2 infall event. There has been evidence that G2 could
cause increased Sgr A* flaring activities. Ongoing multi-wavelength
monitoring of Sgr A* will address this remaining puzzle. |
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Katerina Chatziioannou
Montana State University, Bozeman
Studying the Universe using Gravitational Waves from Compact Binaries
The second generation era of ground-based gravitational wave detectors has just begun. Years of instrument upgrades have led to unprecedented sensitivity and the first direct detection of gravitational waves should be close. Compact binaries of neutron stars and/or black holes hold a prominent role among the possible sources of these gravitational waves. Not only are they one of the most common and well understood sources, but they also carry information that could answer a plethora of questions ranging from the validity of general relativity to the equation of state of the supra-nuclear matter encountered in neutron star interiors. In this talk, I will show how gravitational waves can be used to study the spin and mass distribution of stellar remnants and probe the internal composition of neutron stars. I will describe the strong spin interactions compact binaries exhibit, the rich information these interactions carry, and how they can enhance our understanding of the Universe. |
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For more information, contact:
ciera@northwestern.edu
Past Theory Group Meetings
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