CRA Special Seminar Joheen Chakraborty (Host Dr. Matthew Liska)
2025-10-28 15:30 - 16:30 (America/New_York) | Bogg 1-44 VizLab
Title: Quasi-periodic Eruptions
Abstract: Quasi-Periodic Eruptions (QPEs) are a newly discovered type of recurring X-ray transient originating from supermassive black holes (SMBHs) in nearby, low-mass galaxy nuclei. They are thought to be the first observed counterparts to extreme mass-ratio inspirals (EMRIs), a long-anticipated gravitational wave source class detectable by future space-based interferometers (e.g. LISA). About a dozen QPEs are known, and in an unexpected twist, several of them have emerged from the nascent accretion disks formed by Tidal Disruption Events (TDEs). I will give an overview of the surprising discoveries, observational properties, and theoretical progress in QPEs since their discovery six years ago, including constraints on their emission mechanisms, prospects for probing EMRI orbital dynamics using QPE timings, and estimates of the QPE rate and their implication for EMRI formation. I will also briefly discuss ongoing work regarding the X-ray variability properties of TDEs as probes of their turbulent accretion flows, and electromagnetic study of evolutionary processes in ultracompact binary LISA sources, putting QPEs in the broader context of time-domain and multi-messenger astronomy.

Cosmic Coffee [Howey IZ] Speaker: Mayra Velazquez
2025-10-29 15:30 - 16:30 | Howey IZ, School of Physics, Atlanta, GA, 30332, United States

Cosmic Coffee [Howey IZ] Speaker: Julia Esposito
2025-11-05 15:30 - 16:30 | Howey IZ, School of Physics, Atlanta, GA, 30332, United States

CRA SEMINAR Dr. Christopher Bambic [Prof. John Wise]
2025-11-06 15:30 - 16:30 | Bogg 1-44 VizLab
Title: Coronal Heating and Feedback from Luminous Accretion Flows: Challenges and Insights from Local and Global Simulations
Abstract
Radiatively efficient accretion represents a frontier problem for computational astrophysics. Through leveraging GPU acceleration and exascale supercomputer architectures, the H-AMR Collaboration, led out of Georgia Tech, has been working to understand the structure of accretion flows onto black holes, where strong magnetic fields, two-temperature plasma physics, radiation transport, and general relativity may all imprint themselves on the radiative and kinetic feedback observed from black-hole-powered sources. In this talk, I will discuss our ongoing efforts to model accretion flows across a wide range of accretion rates, from the radiatively inefficient regime powering targets of the Event Horizon Telescope, to the super-Eddington regime, which may be relevant for sources such as tidal disruption events, ultra-luminous X-ray sources, and quasars. Special attention is given to the thin-disk regime at around 1 to a few tens of percent of the Eddington limit, where hard X-ray emission, thought to emerge from a hot (billions of Kelvin) “corona,” is routinely observed. I will discuss two different models for the coronal geometry, the “sandwich” and “truncated disk” models, and what we have learned about possible coronal heating mechanisms based both on the local stratified shearing-box calculations I explored during my Ph.D., and the especially high-resolution global simulations that I have been exploring here at Tech.

Cosmic Coffee [Howey IZ] Speaker: David Raudales
2025-11-12 15:30 - 16:30 | Howey IZ, School of Physics, Atlanta, GA, 30332, United States

CRA SEMINAR - Dr. Arthur Daniel Adams [Dr. Gongjie Li]
2025-11-13 15:30 - 16:30 | Bogg 1-44 VizLab
Title: Mapping Sub-stellar Companions in Time and Space
Abstract: Companion brown dwarfs and exoplanets are complex objects whose time and spatial variability are now being mapped with high-fidelity infrared observations from JWST. I will begin by presenting our analysis of JWST NIRSpec/IFU PRISM observations of the 2M1207 system that represent the first spectroscopic time monitoring of a planetary-mass companion simultaneously with its host. By monitoring the variability of the system as a whole, we are sensitive both to the time evolution of atmospheric structure — including through hot spots and clouds — as well as external variability such as the accretion of disk material. 2M1207 A’s spectra show multiple time-dependent structures across the near-infrared. While we do not see a full rotation within our observations, we do capture non-linear trends in time across much of the spectra, with localized regions showing light curves that hint at the possibility of variability imparted by the circum-stellar disk. The planetary-mass 2M1207 b’s spectra generally corroborate the interpretation of recent atmospheric characterizations, where a simple cloud evolution model can capture most of the short-term variability. Turning to spatial variability, I will also provide a first look at the eclipse mapping of brown dwarfs in orbit around white dwarfs. These systems provide a unique opportunity to study the spatially-resolved structures of highly-irradiated atmospheres. Finally, I will highlight ongoing student research in brown dwarfs and exoplanets at UVA, which includes the spectral and orbital characterization of the aforementioned brown-dwarf/white-dwarf binaries as a complement to atmospheric studies, as well as classifying the seasonal evolution of Earth’s vegetation as spectral signatures of the response of the majority of Earth’s life by mass to the solar energy budget.

Cosmic Coffee [Howey IZ] Speaker: Neil Baker
2025-11-19 15:30 - 16:30 | Howey IZ, School of Physics, Atlanta, GA, 30332, United States

Public talk: Through the Kaleidoscope: The Multicolor Music of Supermassive Black Holes
2025-12-03 19:00 - 20:00 | Howey L1, 800 Atlantic Dr, Atlanta, GA, 30332, United States
Speaker: Prof. Krista Lynne Smith (Texas A&M)
Abstract: The space-time distortion caused by supermassive black holes provides a unique laboratory for violent physical processes. Synthesizing observations across many wavelengths and studying their time variability at slow and rapid timescales promises a new, dynamic, thorough understanding of how black holes form and grow, how they consume material, how they launch powerful relativistic jets, and how they bend the evolution of galaxies to a path that matches our observations of the Universe. I will discuss a brief history of our understanding of these fascinating objects, and discuss how multicolor, time-varying data from new missions has opened new windows into their nature. I will also discuss the rich multi-messenger future of black hole observations, including both neutrinos and gravitational waves.
