Events

President’s Day

There will be no Colloquium today.

Monday, February 17, 2025

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Monday, February 24, 2025 9:30 AM

Revealing Sgr A*’s Mid-IR Flares with JWST/MIRI Observations

Abstract: Sgr A* exhibits flaring activity on hourly timescales at radio, (sub)millimeter, near-IR, and X-ray frequencies. Mid-IR flares, which bridge those observed in the submillimeter and near-IR bands, had remained undetected due to the limited sensitivity and angular resolution of available mid-IR telescopes. The launch of JWST and its MIRI instrument in 2021, with its exquisite photometric stability and sensitivity, enabled us to make the first detection of a mid-IR flare from Sgr A* in April 2024. In this talk, I will discuss our analysis of this first flare. The time evolution of the spectrum at four simultaneously observed mid-IR wavelengths using MIRI’s wide spectral bandwidth found a steepening in its mid-IR spectral index, suggestive of synchrotron cooling. We model the spectral and flux evolution using an orbiting synchrotron hotspot, finding a magnetic field strength of 60-90 Gauss. The derived properties suggest that magnetic reconnection and turbulence are driving particle acceleration. Finally, I will briefly highlight ongoing work with the full 30 hours of MIRI observations obtained in 2024.

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Monday, February 24, 2025 11:00 AM

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Monday, March 3, 2025 11:00 AM

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Monday, March 3, 2025 9:30 AM

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Monday, March 10, 2025 9:30 AM

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Monday, March 10, 2025 11:00 AM

Spring Break

There will be no Foundations Seminar today.

Monday, March 17, 2025

Multi-messenger astronomy with high-energy neutrinos

Abstract: The recent discoveries of high-energy astrophysical neutrinos and gravitational waves have opened new windows of exploration to the Universe. Neutrinos can escape dense environments from where photons can not reach us and travel undeflected through the Universe. In combination with measurements of electromagnetic radiation, neutrinos can help to solve long-standing problems in astrophysics and probe physics that plays a role at extreme conditions that otherwise are hardly accessible to laboratory experiments. For example, TeV-PeV neutrinos have the potential to reveal the origin of cosmic rays. Possible source candidates include the core of active galaxies or the tidal disruption of a star by a supermassive black hole. I will give an overview of recent discoveries in the field of high-energy neutrino astronomy.

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Bio: I did my PhD in 2011 at University of Bonn, followed by a postdoc at SLAC. Then I came back to Germany to lead a Helmholtz Young Investigator group at DESY Zeuthen and since 2021 I’m a professor at Ruhr-University Bochum.

Monday, March 24, 2025 11:00 AM

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Monday, March 24, 2025 9:30 AM

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Monday, March 31, 2025 11:00 AM

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Monday, March 31, 2025 9:30 AM

Model-Based Explication and Quantum Singularity Resolution.

Abstract: There are, at present, no singularity theorems (or resolution theorems) valid for the full domain of quantum gravity. Moreover, lack of empirical data means that a limited range of constraints in model building are available. Finally, limited analytically tractability means most existent treatments are focused on the quantization of finite dimensional truncations of classical cosmological or black hole models — and, even then, often require numerical approaches for exploration of the solutions. These worries notwithstanding, one can certainly ask, and in some cases answer,  physically interesting questions regarding the resolution or not of singularities within this restricted context. The approach is a form of model-based reasoning in which idealized models mediate our understanding of the properties of full, physically representational, theory. In this talk I will consider the idea of model-based explication in the context of refining the concept of singularity resolution, drawing upon my own past work on big bang singularity resolution in quantum cosmology and my current work on black hole singularity resolution.

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Bio: I am an Associate Professor in the Department of Philosophy at the University of Bristol. My current research is principally within physics and the philosophy of physics. My main research focus is the problem of time in classical and quantum theories of gravity. Further topics of current interest include dynamical approaches to symmetry, black hole physics, analogue gravity, quantum cosmology, the arrow of time in quantum theory, the foundations of general relativity, and quantum chemistry. I have written two books: Analogue Quantum Simulation (Springer, 2022) is a monograph on the epistemology of analogue quantum simulation written with Dominik Hangleiter and Jacques Carolan; and Time Regained Volume 1: Symmetry and Evolution in Classical Mechanics (OUP 2023) is the first volume of project on the problem of time with Sean Gryb.

Monday, April 7, 2025 11:00 AM

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Monday, April 7, 2025 9:30 AM

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Monday, April 14, 2025 11:00 AM

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Monday, April 14, 2025 9:30 AM

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Monday, April 21, 2025 11:00 AM

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Monday, April 21, 2025 9:30 AM

Event Horizon and Environs (ETHER)

Abstract: To date, the Event Horizon Telescope (EHT) has imaged only two supermassive black holes at resolutions finer than 50 gravitational radii: M87 and SgrA*.
Ongoing and planned upgrades to the EHT enable demographic studies
of black holes at these scales – the focus of this talk.

We will present the Event Horizon and Environs (ETHER) sample of single and
binary black holes, a curated database for selection of (current and future) EHT targets. We will also present the progress in imaging  single black holes in ETHER with the EHT, and the expectations of imaging and monitoring binary black holes into the future. Finally, we will discuss a newly identified population of the most massive black holes (thus the largest black hole shadows) in the nearby universe, and its implications for the EHT.

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Bio: Neil Nagar is a professor at the University of Concepcion, Chile, and a member of the Event Horizon Telescope Collaboration. He is is the Director of the ‘TITANs Millennium Nucleus’, a group of forty researchers and students across four universities in Chile. Nagar graduated as an engineer and mathematician at BITS, Pilani, India, before completing his Doctorate in Astronomy at the University of Maryland, College Park in 2000.

Nagar’s interests include supermassive black holes, galaxy evolution, and the origin of ultra high energy cosmic rays.

Monday, April 28, 2025 11:00 AM