Physics Seminar

The Microphysics of AGN Feedback

Speaker: Dr. Hsiang-Yi Karen Yang (University of Maryland)
Location: OPB 234, 2:50pm
Abstract: Feedback from active galactic nuclei (AGN) is one of the most important processes governing the formation and evolution of galaxies and galaxy clusters. It is believed to be responsible for inhibiting the formation of massive galaxies and for solving the long-standing "cooling-flow problem" in galaxy clusters. A lot of understanding of AGN feedback has been gained using hydrodynamic simulations; however, some of the relevant physical processes are unresolvable or not captured by pure hydrodynamics, such as plasma effects and cosmic-ray (CR) physics. In this talk, I will present how we use simulations that incorporate this "microphysics" to understand how AGN jets feedback on galactic and cluster scales. Specifically, I will discuss the roles of thermal conduction and CRs in addition to purely hydrodynamic models. I will also talk about how we could use multi-messenger observations of the Fermi bubbles as a nearby aboratory for studying AGN feedback. Finally, I will conclude with open questions and future prospects of applying simulations beyond hydrodynamics to various interesting astrophysical systems.

No Seminar Today - UAH Honors Day

Galaxy Clusters, Shock Waves, and Cosmic Home Runs

Speaker: Dr. Roger Blandford (Stanford)
Location: OPB 234, 2:50pm
Abstract: We observe Ultra High Energy Cosmic Rays with energies over 100 EeV that are probably produced with ten times this energy. We do not understand their provenance but simple physical principles limit the options. The arguments in favor of particle acceleration at intergalactic shock fronts will be rehearsed and some tests of this explanation will be proposed.

Reverse Engineering the Universe

Speaker: Dr. Roger Blandford (Stanford)
Location: MSC 100 (Materials Science Building Connector), 6:00pm
Abstract: Careful observations over the past sixty years guided by basic principles of physics including, especially, Albert Einstein’s General Relativity, have allowed cosmologists to reconstruct the history of the universe and to describe it using a remarkably simple standard model. This narrative begins with an epoch of rapid acceleration, called inflation when the seeds of contemporary structure were sown. This was followed by a period decelerating expansion while the universe, cooled off. In recent times it has started to accelerate again due to the dominance of a cosmological constant. This standard model has proven to be quite resilient but leaves many questions unanswered. The model, the evidence for it and the prospects for building upon it will be described.

No Seminar. UAH Spring Break

Electron Injection at Shocks of Young Supernova Remnants

Speaker:Dr. Jacek Niemic (Polish Academy of Sciences)
Location: OPB 234, 2:50pm
Abstract: Particle pre-acceleration constitutes a central unresolved problem for diffusive shock acceleration process. This mechanisms acting at nonrelativistic shocks of young supernova remnants is thought to provide the main flux of Galactic cosmic rays. In my talk I will report on recent studies of high-Mach number perpendicular and quasi-perpendicular shocks with fully kinetic two- and three-dimensional particle-in-cell simulations. I will summarise the current status of understanding a nonlinear, large-scale, and time-dependent structure of high-Mach number shocks in multi dimensions and discuss mechanisms and conditions leading to efficient electron pre-acceleration.

Optics Challenges of a Wide-Field of View, Large Aperture Imager for EUSO-SPB2: Second Generation Extreme Universe Space Observatory on a Super-Pressure Balloon

Speaker: Dr. Patrick Reardon (UAH CAO)
Location: OPB 234, 2:50pm
Abstract: UAH has recently been awarded a NASA funded project to, in part, develop and assist in assembly and deployment of a wide field of view, low F/# optic as a part of a multi-university project with international support. The goal of this project is to acquire data on ultra-high energy cosmic rays (UHECRs) by recording their fluorescence as they interact with Earth's atmosphere, and cosmogenic tau neutrinos (CTNs) by sensing the Cherenkov radiation from up-going tau decays produced by the cosmogenic neutrinos as they pass through the earth's crust and re-enter the atmosphere as upwelling particles. This talk presents the limited specifications and goals provided to guide the optics design, and how those specifications led to the initial design solution, a system based on the Schmidt Telescope form. The challenges and advantages for this optical design are discussed, with comparisons to far different optics approaches that have been both proposed and flown.

Ultrafast pump-probe spectroscopy, using a prism coupler to launch light into the multilayer waveguide, allowed us to study free carrier absorption (FCA) and carrier dynamics in Si nanostructures. Optical confinement in the low refractive index medium (Er - doped SiO2) for TM polarization was used to suppress FCA process in nm-thick layers containing Si nanocrystals.

Towards a Si-based Laser-Efficient Infrared Emission from Er-doped SiO2/nc-Si Multilayers

Speaker: Dr. Helina Krzyzanowska (Vanderbilt)
Location: OPB 234, 2:50pm
Abstract: Silicon photonics was pioneered in the 90’s by Richard Soref. Despite much research, highly efficient light sources based on silicon have not yet been realized. One of the most promising ways of achieving efficient electrically pumped Si light sources at the standard telecommunication wavelength (1535 nm) is to use the unique properties of Si nanostructures doped with rare earth ions.

This talk covers optical and electrical studies of Er doped SiO2/nc-Si multilayers fabricated by RF magnetron sputtering. Understanding and optimization of energy transfer from the Si nanocrystals to Er, suppression of free carrier absorption in nc-Si, and efficient current flow through nm-thick nc-Si are key elements to achieve luminescence from Si-based light source.

The studies of visible and infrared photoluminescence and time resolved photoluminescence reveal efficient energy transfer from the multilayers.

Ultrafast pump-probe spectroscopy, using a prism coupler to launch light into the multilayer waveguide, allowed us to study free carrier absorption (FCA) and carrier dynamics in Si nanostructures. Optical confinement in the low refractive index medium (Er - doped SiO2) for TM polarization was used to suppress FCA process in nm-thick layers containing Si nanocrystals.

Carrier transport and infrared electroluminescence under a lateral device geometry was studied as a function of various parameters. The major advantage of the proposed lateral carrier injection approach compared to vertical one, is that transport is much easier in the multilayers. It proceeds inside the Si layers instead of through an oxide matrix.

The strong photoluminescence under off-resonance excitation and electroluminescence under forward bias are very promising for Si-based light sources - the missing link in an all-silicon on-chip optical interconnection system.

Broadband Reflective Multilayer Coatings for X-ray Optics

Speaker: Ms. Danielle Gurgew (UAH Physics & Astronomy)
Location: OPB 234, 2:50pm
Abstract: The principle goal of this research is the development of a broadband X-ray multilayer coating to be used for focusing astronomical X-ray radiation in the 1 - 200 keV energy band. The implementation of this new technology will enable scientists to disentangle various X-ray source mechanisms, leading to an improved understanding of the evolution of the universe. Based on this scientific motivation, the development of these coatings has been undertaken including the installation of a new multilayer coating deposition system and X-ray reflectometer system for conducting tests at NASA Marshall Space Flight Center. The initial results of the optimization and development of a novel multilayer coating for hard X-ray optics are presented.

Investigation of Terrestrial Gamma-ray Flashes (TGFs) Production Mechanisms

Speaker: Mr. Samer Al-Nussirat (UAH Physics & Astronomy)
Location: OPB 234, 2:50pm
Abstract: Since the launch of the Geostationary Lightning Mapper (GLM) in late 2016, and its validation in 2017, valuable observations of lightning optical emissions over the northern hemisphere became available. These observations can be used along with TGFs detected by the Gamma-ray Burst Monitor (GBM) to study the production mechanism of TGFs. This talk will review the TGF production mechanisms and present the first results of their correlation with space-based observations of lightning optical emissions.

The Physics of Drug Discovery

Speaker: Dr. Jerome Baudry (UAH Biology)
Location: OPB 234, 2:50pm
Abstract: Drug (pharmaceutical) discovery is a very interdisciplinary process that integrates together chemistry, physical chemistry, biology, and mathematics, amongst other fields. But at the heart of modern, i.e., computational, drug discovery are concepts and methods of physics. I will describe how our research in the field of drug discovery uses methods and results in quantum physics and quantum chemistry, in solid-state and soft-matter physics, and in classical Newtonian physics.

The Continuing Quest for a Detailed Model of Type Ia Supernovae

Speaker: Dr. Dean Townsley (UA Physics & Astronomy)
Location: OPB 234, 2:50pm
Abstract: While Type Ia Supernovae are widely depended upon for accurate measurements of the expansion history of the universe, many aspects of their origins remain unknown. Improved simulations and observations in the last decade have only made this situation more unclear. While we know from the material ejected that these supernovae must come from the explosive incineration of a white dwarf star, exactly how and, more critically, why this explosion takes place and what type of stellar systems produce it are ambiguous. I will present two current leading candidate scenarios, including their strengths and weaknesses in explaining the observed properties of Type Ia Supernova populations. Computing the predicted results of these scenarios requires accurate and efficient numerical modeling of the combustion of carbon and helium-rich material on stellar scales in both the deflagration and detonation mode. I will discuss some of the challenges met in computing accurate combustion dynamics and products for a star with dimensions of thousands of kilometers incinerated by reaction fronts with thicknesses of various processes spanning from millimeters to megameters.

STROBE-X: X-ray Timing & Spectroscopy on Dynamical Timescales from Microseconds to Years

Speaker: Dr. Colleen Wilson-Hodge (NASA MSFC)
Location: OPB 234, 2:50pm
Abstract: We describe a probe-class mission concept that provides an unprecedented view of the X-ray sky, performing timing and 0.2-30 keV spectroscopy over timescales from microseconds to years. The Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X) comprises three primary instruments. The first uses an array of lightweight optics (3-m focal length) that concentrate incident photons onto solid state detectors with CCD-level (85-130 eV) energy resolution, 100 ns time resolution, and low background rates to cover the 0.2-12 keV band. This technology is scaled up from NICER, with enhanced optics to take advantage of the longer focal length of STROBE-X. The second uses large-area collimated silicon drift detectors, developed for ESA's LOFT, to cover the 2-30 keV band. These two instruments each provide an order of magnitude improvement in effective area compared with its predecessor (NICER and RXTE, respectively). Finally, a sensitive sky monitor triggers pointed observations, provides high duty cycle, high time resolution, high spectral resolution monitoring of the X-ray sky with ~20 times the sensitivity of the RXTE ASM, and enables multi-wavelength and multi-messenger studies on a continuous, rather than scanning basis. We include updated instrument designs resulting from the GSFC IDL run in November 2017.

 

For the first time, the broad coverage provides simultaneous study of thermal components, non-thermal components, iron lines, and reflection features from a single platform for accreting black holes at all scales. The enormous collecting area allows detailed studies of the dense matter equation of state using both thermal emission from rotation-powered pulsars and harder emission from X-ray burst oscillations. The combination of the wide-field monitor and the sensitive pointed instruments enables observations of potential electromagnetic counterparts to LIGO/Virgo and neutrino events. Extragalactic science, such as constraining bulk metalicity of medium to high redshift clusters and nearby compact groups and unprecedented timing investigations of active galactic nuclei, is also obtained.

Dense Molecular Gas and Star Formation in Nearby Galaxy M51

Speaker: Dr. Hao Chen (UAH Physics & Astronomy)
Location: OPB 234, 2:50pm
Abstract: Stars form in the dense cores of giant molecular clouds (GMCs). The dense cores are traced by high-dipole-moment molecules such as HCN and HCO+. The star formation rate (SFR, traced by infrared luminosity) and dense molecular gas mass (traced by HCN luminosity) show linear correlation in global galaxies. It is a front topic in astrophysics that how does the dense gas form stars in galactic disk. We mapped dense molecular gas (traced by HCN 1-0 emission) across the disk of M51 with IRAM 30m telescope and find that the star formation efficiency of dense gas (IR to HCN luminosity ratio) is lower in the center than in the outer disk. This could be caused by the stronger turbulence in the center which could prevent the formation of stars from dense gas. We also detected dense gas (traced by HCN 1-0 and HCO+ 1-0) in 6 giant molecular associations (GMAs, ~100pc) with NOEMA telescope in the spiral arms of M51. Comparing with multi-scale targets (global galaxies, 1 kpc scale regions in the disk of nearby galaxies, giant molecular associations and dense molecular cloud cores in the Milky Way), we confirm that the linear relation between IR and HCN luminosity extend to the spatial scale of 100 pc.