Events

Giacomo Fragione
Center for Interdisciplinary Exploration and Research in Astrophysics
Northwestern University

Hierarchical Black Hole Mergers: A Multi-band Opportunity for Gravitational Waves

With about a hundred binary black hole (BBH) mergers detected via gravitational wave (GW) emission, our understanding of the darkest objects in the Universe has seen unparalleled steps forward compared to previous decades. While most of the events are expected to consist of first-generation BHs formed from the collapse of massive stars, others might be of a second or higher generation, containing the remnants of previous BH mergers. A fundamental limit for hierarchical mergers comes from the recoil kick imparted to merger remnants, which could result in the ejection from the host star cluster. However, hierarchical mergers can build up massive BHs and even form intermediate-mass black holes if the host cluster is massive and dense enough, as in nuclear star clusters and the most massive globular clusters. With their distinctive signatures of higher masses and spins, hierarchical mergers offer an unprecedented opportunity to learn about the densest systems in our Universe and to shed light on the elusive population of intermediate-mass black holes. The next years may bring hundreds of detections from hierarchical mergers with multi-band events chirping from space-based to ground-based detectors, promising a spectacular range of new science from stellar evolution to cosmology.

There will be refreshments at 3:45 pm in Lewis 104.

Matthew Route
Department of Physics and Astronomy
University of Mississippi

Substellar Magnetism at Radio Wavelengths

Lurking between low mass stars and exoplanets on the mass scale lie ultracool dwarfs, which share characteristics with both classes of objects.  Perhaps some of the most surprising discoveries among ultracool dwarfs are that they host strong, kG-strength magnetic fields and are powerful radio-emitters, despite their exoplanet-like effective temperatures and neutral atmospheres.  However, many unanswered questions remain regarding their magnetic activity, including what are the characteristics of their magnetic dynamos, what is the nature of the electrodynamic engine that triggers magnetic reconnection to accelerate radio-emitting electrons, and what is the origin of the emitting plasma.  One intriguing theory is that their radio emissions may be triggered by scaled-down star-planet magnetic interactions.  Radio observations present an unprecedented opportunity to probe brown dwarf magnetic activity, examine the characteristics and functioning of dynamos among fully-convective objects, and investigate the nature of exoplanet magnetism.

There will be refreshments at 3:45 pm in Lewis 104.

Michael Fausnaugh
Kavli Institute for Astrophysics and Space Research
Massachusetts Institute for Technology

Transient Science with TESS and Frontiers in Time Domain Astronomy

Modern sky surveys are observing large swaths of the sky each night, even while pushing to faster and faster time sampling. As a result, the number of supernovae and other transient astrophysical explosions discovered per year is growing at an exponential rate. At the same time, densely sampled light curves produced by these surveys are enabling new scientific investigations. I will discuss recent results in extragalactic astronomy that my team has produced using some of these new observing facilities, particularly The Transiting Exoplanet Survey Satellite (TESS). In particular, I will present TESS light curves of 300 Type Ia supernovae and our search for companion star interactions. I will also show how time domain monitoring data of actively accreting supermassive black holes (quasars) can be used to map material within a few hundred gravitational radii of the black hole. Finally, I will discuss applications of TESS for electromagnetic follow-up of gravitational wave events from the LIGO-Virgo-KAGRA network, and other prospects for observing exotic transient events over the next decade.

There will be refreshments at 3:45 pm in Lewis 104.

Nicholas MacDonald
Radio Astronomy/VLBI Group
Max Planck Institute for Radio Astronomy

Blacks Holes, Relativistic Blazar Jets, and Global Very Long Baseline: Interferometry
High Energy Astrophysics in the Roaring 20s

Blazars are an extreme subclass of active galactic nuclei (AGN), in which an accreting supermassive black hole launches a powerful relativistic jet of magnetized plasma that is closely aligned to our line-of-sight. Blazar jets: (i) shine across the entire electromagnetic spectrum (from low-frequency radio waves to high-energy gamma-rays), (ii) exhibit dramatic flares (on time scales ranging from days to minutes), and (iii) dominate the high-energy extragalactic sky. Very long baseline interferometric (VLBI) arrays (such as phased ALMA and The Event Horizon Telescope) are capable of imaging the polarized synchrotron emission emanating from the innermost regions of relativistic blazar jets with unprecedented angular resolution and sensitivity. In particular, the linearly and circularly polarized synchrotron emission from blazar jets carry imprints of both the strength and orientation of the collimating magnetic field as well as the plasma content of the jet environment. In parallel to these advances in VLBI imaging, modern computational resources now support the execution of increasingly sophisticated 3D numerical jet simulations, from shock-in-jet/turbulence models, to relativistic magneto-hydrodynamic (RMHD) and particle-in-cell (PIC) plasma simulations. In this talk, I will present a new suite of relativistic jet simulations which study the synchrotron polarization produced by blobs of relativistic plasma passing through standing recollimation shocks in the jet. This is accomplished through the use of the PLUTO code in concert with polarized radiative transfer ray-tracing calculations computed using the RADMC-3D code. The physical implications of this synchrotron emission will be discussed and direct comparisons will be made to actual VLBI observations of relativistic blazar jets.

There will be refreshments at 3:45 pm in Lewis 104.

Nihan Pol
Department of Physics and Astronomy
Vanderbilt University

Exploring the Gravitational Wave Landscape with Pulsars

Pulsars, which are rapidly rotating neutron stars, are a unique celestial object that can serve as both source and detector of gravitational waves (GWs). In this talk, I will give an overview of how multi-messenger observations of binary pulsar systems can shed light on the population of these systems in our Galaxy and present methods for optimizing current radio pulsar searches to find ultra-compact binary pulsars that will be visible with LISA. Finally, I will describe how millisecond-period pulsars can be used to construct a GW detector that is sensitive to nano-hertz frequency GWs and present results from the latest, most sensitive search for these GWs and the expectations for these detectors in the next few years.

There will be refreshments at 3:45 pm in Lewis 104.

Ayush Dhital, Aniket Khairnar
Department of Physics and Astronomy
University of Mississippi

Student Research Presentations

Graduate students in the Department of Physics and Astronomy will present brief reports on their ongoing research.

There will be refreshments at 3:45 pm in Lewis 104.

Tiffany Lewis
Astroparticle Physics Lab
Goddard Space Flight Center

Building Blocks for Blazars

This talk examines what that means from a variety of perspectives - the concept of cosmic scale, the components of the system, and the physical processes we think we observe, all to frame how I think about modeling them, and to set up how I think about future projects and their larger context. We begin by building up the concept of scale in the universe through the lens of light travel time for the purpose of defining blazar size and distance between galaxies. Then, we will explore the structure and characteristics of active galaxies before diving into the physics of blazar jets, how it is studied and some key findings about the importance of particle acceleration and the limitations of current multi-wavelength observations. We will then examine a suggested direction for the field of astrophysics and some thoughts on programmatic balance among the suite of missions NASA will solicit over the coming decades.

There will be refreshments at 3:45 pm in Lewis 104.

Akshay Khadse, Nathan Hill
Department of Physics and Astronomy
University of Mississippi

Student Research Presentations

Graduate students in the Department of Physics and Astronomy will present brief reports on their ongoing research.

There will be refreshments at 3:45 pm in Lewis 104.

Woodrow Shew
Department of Physics
University of Arkansas

Brain on the Edge: Phase Transitions and Criticality in Cerebral Cortex

When many neurons interact, complex collective brain dynamics emerge. When the interactions among neurons are altered (e.g. by chemicals that affect alertness), brain dynamics can undergo a phase transition, dramatically changing from an ordered phase to a disordered phase, similar to the collective behavior of water molecules when transitioning from liquid to gas phase. In this talk, I will introduce and provide historical context for a somewhat controversial hypothesis at the interface of physics and neuroscience and share our recent experiments and data analysis that help resolve the controversy. The hypothesis is that the awake cerebral cortex operates in a critical phase near a transition boundary between ordered and disordered dynamics. Some previous experiments support this hypothesis, but others seem to contradict it. Here I will show that proper consideration of coarse-graining the observable microscopic variables (spikes of neurons), zooming out to the macroscopic level, is essential to reveal critical dynamics in awake brains. Another way to interpret this result is that brain dynamics are very high-dimensional, but critical dynamics exist in a low-dimensional subspace (if you like linear algebra, you might enjoy this interpretation). I will strive to make this talk accessible to those with no expertise in neuroscience and almost no expertise in the physics of phase transitions.

There will be refreshments at 3:45 pm in Lewis 104.

Alexey Petrov
Department of Physics and Astronomy
University of South Carolina

Marvelous Muons: Searching for New Physics with Bound States

Indirect searches for New Physics are the searches for quantum effects of new particles that can be discovered by observing tiny deviations between theoretical predictions and experimental observations. I will discuss how physicists have been using bound muons to probe New Physics that is not reachable by direct searches at the Large Hadron Collider.

There will be refreshments at 3:45 pm in Lewis 104.

Zhongzhou Chen
Department of Physics
University of Central Florida

Towards a Student-centered Mastery-based Online STEM Learning Environment

In the majority of today's STEM courses, students “march forward” at a uniform pace over the semester, regardless of their current status and previous backgrounds. Instructors teach largely the same course repetitively, with few rigorous and effective tools to evaluate the effectiveness of instruction and make significant improvements. In the student-centered, mastery-based STEM online learning environment of the future, students can proceed at different pace based on their level of mastery and background, guided by frequent self-assessment and feedback. The instructor's role will be transitioned into a designer, making data driven learning design improvements to the course. My past efforts toward creating such a learning environment can be roughly divided into three stages. First, an early prototype of online mastery-based learning modules for University physics I, was created on the open-source platform of Obojobo by UCF Center for Distributed Learning. Second, students' learning strategy and learning behavior is identified from click-stream data, and visualized using learning analytics techniques such as process mining. Third, data informed improvements of instructional design were implemented as natural experiments and evaluated using analysis methods such as “differences in differences”. Finally, my latest research focuses on creating mastery-based assessments, by harnessing the power of AI to create large isomorphic assessment problem banks. This new type of exam can be administered asynchronously, allow infinite number of attempts, openly shared and collaboratively developed, and are essentially “Chegg proof”. They will serve as stable “anchor points” for mastery-based learning environments.

There will be refreshments at 3:45 pm in Lewis 104.

Umberto Tamponi
Researcher, Istituto Nazionale di Fisica Nucleare (INFN)
Sezione di Torino Instituto Nazionale di Fisica Nucleare

Quarkonium and the New Landscapes of QCD

This seminar aims to show you how quarkonium is an extraordinary tool to explore the behavior of a strongly-coupled theory, in this case quantum-chromodynamics (QCD), in its transition from the perturbative to the non-perturbative regime. Quarkonium is a family of states with mass between 3 and 10 GeV/c² usually described as bound states of a heavy quark and its antiquark. In such systems a hierarchy of energy scales naturally emerges: from the soft, non-perturbative scale that controls the spectrum to the hard scale of the annihilations. At each of these scales we are now observing unexpected phenomena, all connected to the emergence of light degrees of freedom inside the heavy meson. In this seminar I will introduce the basic features of quarkonia, review the most important recent progresses in connection with our understanding of QCD in the non-perturbative regime and finally outline the future lines of research in this field, with a focus on the experimental facilities.

There will be refreshments at 3:45 pm in Lewis 104.