UNLV Department of Physics and Astronomy

Forum Schedule:  Fridays 3:45pm - 4:45pm

DateSpeakerTitle & Abstract
Jan 24
Jan 31
Feb 7
Feb 10
(Monday 10:00AM)
Stas Sinogeikin
(host: Andrew Cornelius)
High-Pressure/Low Temperature Research at HPCAT at the Advanced Photon Source
Feb 14Dr. Marcelo Alvarez
(Canadian Institute for Theoretical Astrophysics)
(host: Dr. George Rhee)
Computational Cosmology in the Era of Big Data: Simulating the Observable Universe
We are entering an exciting new time in cosmology. New observational campaigns with such facilities as the Large Synoptic Survey Telescope and the Square Kilometer Array will revolutionize the amount of information available to us about the large scale structure of the universe, generating many petabytes of data. Making sense of all this data will require computer simulations accurate over a much larger dynamic range than currently possible. I will describe the current open questions that can be answered with this data and present the new computational approaches we are developing to tackle this problem.
(Wednesday, 3:45PM)
Dr. Kayhan Gultekin
(University of Michigan)
The ABC's of Supermassive Black Holes: Accretion, Binaries, and Coevolution
It has been over a decade since the discovery that the mass of a central black hole scales with the properties of its host galaxy. Because of these remarkable scaling relations, the idea that galaxies and black holes coevolve through some sort of self-regulated feedback has come to dominate scientific discussion. But do we really understand what the scaling relations are telling us? I will review state of the field and present recent developments from the observational perspective of the black hole scaling relations, including our discovery of a 1.7e10 solar mass black hole in a galaxy with stellar mass only 1.2e11 solar masses, discussing how well coevolution models and their alternatives can handle this. In addition to coevolution, the scaling relations in the local universe inform the study of formation of black hole seeds, black hole density functions across cosmic time, and the disputed claims of evolution of the scaling relations with redshift. I will discuss my new empirical-observational tool for using X-ray and radio measurements to measure black hole masses and understand the physics of accretion and outflow. The history of searches for binary supermassive black holes is riddled with false positives and controversial findings. I will present recent and in-progress theoretical calculations to describe the electromagnetic signature of an accreting supermassive black hole with a small companion. This will lead into future observational searches for the tightest binary supermassive black holes. I will conclude by exploring what important, observational and theoretical questions still need to be answered.
Feb 21Dr. Rebecca Martin
(JILA, University of Colorado)
Formation of Habitable Planets
I will review the long term evolution of protoplanetary discs around young stars and circumplanetary discs around forming gas giants. I will discuss the formation and architecture of our solar system and how it was shaped by the evolution of various snow lines within the solar nebula. I will explain how the Earth was able to form with such a small fraction of water and discuss implications of the models for the habitability of extra solar planets.
Feb 27Dr. Kengo Tomida
(Princeton University)
(host: Dr. Daniel Proga)
Global MHD Simulations of Star-Disk Interaction
In the final phase of the star formation processes, gas accretes through circumstellar disks onto protostars, and the disk and the protostar interact each other via magnetic fields in the innermost region. The structure of the accretion flow in this region is determined by the strength of the stellar magnetic fields and the accretion rate, which depends on angular momentum transport by turbulence driven by the Magneto-Rotational Instability (MRI). Therefore, high resolution MHD simulations are required to study the structure of the accretion flow. For this purpose, we have extended Athena MHD simulation code (Stone et al. 2008) by implementing a new MHD solver for spherical polar coordinates. We performed MHD simulations similar to Romanova et al. (2012) with sufficient resolution to resolve MRI within the disk. The properties of turbulent accretion disks with weak magnetic fields are similar to those obtained in local shearing box simulations. On the other hand, when magnetic fields are moderately strong, we find that magnetosphere can be collapsed by strong accretion flow driven by interplay of magnetic interchange instability and magnetic braking.
Feb 28Dr. Raffaella Margutti
(Harvard CfA)
(host: Dr. George Rhee)
Explosive Transients in the era of Time Domain Astronomy
Stellar explosions are at the intersection of several critical areas of modern Astronomy: as probes of the early Universe, as electromagnetic signposts of gravitational wave and neutrino emitters, as laboratories for extreme physics. In this talk I present the recent results from my multi-wavelength effort designed to (i) constrain the stellar progenitors and their evolution in the years before the terminal explosion; (ii) shed light on the physical mechanism that enables only a small fraction of stellar explosions to harbor and launch a relativistic jet. By taking advantage from DISCOVERY -provided by observations of the transient sky- and DEEP-INSIGTH -that only a truly multi-wavelength perspective can offer-, I show how this study paves the way to the upcoming era of multi-messenger astronomy.
Mar 7
Mar 14Dr. John Neumeier
(Montana State University)
(host: Dr. Andrew Cornelius)
Anisotropic Solids -- What makes them interesting and potentially important?
Mar 21Spring Break
Mar 28Joe Thompson
(Los Alamos National Lab)
(host: Dr. Andrew Cornelius)
Magnetism and Superconductivity in Heavy-Fermion Materials
Apr 4
Apr 11
Apr 18
Apr 25Prof. Pawan Kumar
(University of Texas, Austin)
(host: Dr. Bing Zhang)
Recent Advances in our Understanding of gamma-ray bursts
After a brief summary of key observational properties of gamma-ray bursts I will describe recent advances to our understanding of the emission mechanism. I will describes the strength and weaknesses of the various models. The high energy gamma-ray radiation detected by the Fermi satellite from GRBs and their origin will also be discussed. A brief summary of our understanding of the GRB central engine will also be provided.
May 2Dr. Eric Bauer
(Los Alamos National Lab)
(host: Dr. Andrew Cornelius)
Quantum Criticality in CeMln5 and PuMX5 (M=Co, Rh; X=Ga, In) Superconductors
The discovery of superconductivity in PuCoGa5 with a transition temperature of Tc = 18.5 K [1] has generated renewed interest in Pu-based intermetallic compounds. PuCoGa5, and its superconducting cousin PuRhGa5 (Tc = 8.7 K) [2], have the same crystal structure as a growing class of tetragonal CeMIn5 (M=Co, Rh, Ir) heavy fermion superconductors, suggesting that the structure plays a key role in generating superconductivity in these materials. While a variety of measurements have firmly established that the CeMIn5 compounds are unconventional d-wave superconductors, most probably mediated by antiferromagnetic spin fluctuations, it is less clear what drives the high transition temperature in PuCoGa5, which is an order of magnitude larger than all other known Ce- or U-based heavy fermion superconductors. The physical properties of two new members of this "115" family of superconductors, PuRhIn5 and PuCoIn5 [3], along with the observation of long-range antiferromagnetic order in PuRh(In,Cd)5, indicates that these PuMIn5 (M=Co, Rh) reside close to an antiferromagnetic quantum critical point [4]. Recent measurements [5] of all of the elastic moduli of PuCoGa5 delineate the temperature evolution of each symmetry channel; in contrast with the ordinary behavior of the shear moduli, the compressional moduli exhibit anomalous softening upon cooling and over a broad temperature range, which is truncated at the superconducting transition. The anomalous softening suggests that PuCoGa5 is near a critical-end point of a valence transition, whose slow fluctuations are intimately involved in the unconventional superconductivity. The nature of the quantum criticality in the PuMX5 materials and its connection to the unconventional superconductivity will be discussed.
May 9
(Beginning 10:00AM)
Physics and Astronomy SeniorsPHY-493 Presentations
May 16Finals Week

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