Physics Colloquia

Studying Magnetism with Resonant X-ray Scattering at Advanced Photon Source
Jong-Woo Kim, Physicists
Magnetic Material Group/Advanced Photon Source, Argonne National Laboratory

X-ray scattering at synchrotron facilities such as the Advanced Photon Source provides a powerful platform for investigating magnetic order with element and orbital specificity. In this colloquium, I will introduce the fundamentals of single-crystal X-ray diffraction and the principles of resonant elastic X-ray scattering (REXS), emphasizing how tuning to absorption edges enhances sensitivity to electronic and magnetic structures.

Constraining Common Envelope Evolution Simulations with Observations
Sarah Villanova Borges, PhD Candidate
University of Wisconsin-Milwaukee

Common Envelope Evolution (CEE) remains one of the biggest unresolved problems in binary stellar evolution, despite being the primary pathway for the formation of close binary systems. One of the main challenges in understanding CEE is its intrinsically multiscale and multiphysics nature, which makes it difficult to model with analytical or 1D models. 3D hydrodynamical simulations have therefore become essential tools for studying this phase. However, validating these simulations requires observational constraints, which are scarce. This lack of direct observations is another major obstacle in modeling CEE. One exception is luminous red novae, which is believed to correspond to CEE events that culminate in stellar mergers.

Gravitational Waves from Galactic Nuclei
Nicholas Stone, Assistant Professor
Department of Astronomy, University of Wisconsin-Madison

The discovery of GW150914 inaugurated the era of gravitational wave (GW) astronomy, opening a new window to study our Universe's compact objects and through which to test general relativity. Now, a decade later, the LIGO-Virgo-KAGRA (LVK) collaboration has seen hundreds of GW signals, overwhelmingly from mergers of binary stellar mass black holes. Despite the many successes of GW astronomy, a zeroth-order astrophysical question remains unanswered: what astrophysical environments produce the LVK binary black holes, and by what process are they assembled? Although many formation channels have been proposed, one uniquely testable solution is the "AGN channel:" a scenario in which individual black holes pair up and merge in the dissipative gaseous environment of an active galactic nucleus.

Novel Imaging Techniques for Studying Interactions of Membrane Receptors Among Themselves and with Downstream Signaling Partners
Thomas D. Killeen, PhD Candidate
University of Wisconsin-Milwaukee Department of Physics & Astronomy

Cells rely on complex signaling networks to sense and respond to environmental stimuli, but the bigger picture of how molecular assembly leads to robust cellular signaling is only beginning to emerge. A major challenge in characterizing cellular signaling is the ability to directly observe the dynamic interactions between membrane receptors and intracellular signaling partners in living cells. To address this challenge, this work presents the development of advanced fluorescence imaging and computational analysis tools designed to improve the precision and quantitative power of live-cell micro-spectroscopy for studying protein dynamics in real time.