Center for Relativistic Astrophysics

SPRING BREAK March 18 -March 22
2024-03-18 | GA

CRA Seminar: Yuan-Sen Ting (ANU)
2024-03-14 15:30 - 16:30 (America/New_York) | Bogg 1-44 VizLab
Title: Transcending the Limits of Theoretical Physics with Deep Learning
Abstract: Astronomy has recently experienced a profound transformation, driven by the acquisition of extensive datasets generated by increasingly sophisticated instruments. This influx of data has opened up numerous new avenues for exploration in the field. However, this boon is accompanied by its own set of challenges, as astronomical phenomena often exhibit intricate and are inherently high-dimensional. These complexities involve precise imaging, spectral analysis, and time series data.
Traditional statistical methods in astronomy can struggle to effectively handle these complexities. Deep learning offers a solution by effectively addressing the challenges by allowing for a more faithful representation of the intricate astronomical phenomena. In this talk, I will delve into deep learning approaches for characterizing complex astronomical systems. Additionally, it will explore the theoretical underpinnings of deep learning, including its close relationship with symmetry and physics. This exploration will encompass a diverse range of applications in astronomy, including asteroseismology, stellar spectroscopy, weak lensing, reionization, galactic dynamics, galaxy evolution, and quasars. These applications collectively contribute to expanding the boundaries of Bayesian statistics and theoretical astrophysics, all within the framework of deep learning.

Cosmic Coffee (Howey IZ)
2024-03-13 15:30 - 17:00, 2024-03-06 15:30 - 16:30, 2024-02-28 15:30 - 16:30, 2024-02-21 15:30 - 16:30, 2024-02-14 15:30 - 16:30, 2024-02-07 15:30 - 16:30, 2024-01-24 15:30 - 16:30, 2024-01-17 15:30 - 16:30 | GA

CRA Seminar: Labani Mallick (U Manitoba) Virtual
2024-02-29 15:30 - 16:30 | GA
Title: Impact of Central Massive Black Hole Accretion on the Event Horizon, Host Galaxy, and Beyond
Abstract:
Astrophysical black holes are surprisingly simple physical objects. Their gravitational field can be fully described by two parameters: mass and spin. We cannot directly observe black holes as no light escapes from the event horizon. However, we can detect the light from accreting gas, which forms a dense disk around the black hole, known as an accretion disk. The accretion of material by a massive black hole at the center of its host galaxy forms an active galactic nucleus (AGN), the innermost region of which emits X-ray radiation. An AGN is energetically efficient for regulating the growth of galaxies and is crucial for the development of the Universe we see today. One of the most important tools to probe the innermost accretion flow is the detection of X-ray reverberation echoes, where the X-ray photons reflected from the accretion disk are delayed relative to the primary X-ray source. In this talk, I will first discuss how detailed measurements of the reflected X-rays from the accretion disk can be used to probe the innermost regions of accretion flow just outside the event horizon and determine the fundamental properties of the black hole, such as its spin, across the complete mass scales from ∼ 105 −1010 solar masses. Peering into the growth
channels of black holes, I will discuss how we can distinguish accretion vs. merger-dominated black hole growth and probe the cosmological evolution of black hole spins in the last 10 billion years of cosmic history. Finally, I will show how enigmatic relativistic winds or Ultra-Fast Outflows (UFOs) launched from the AGN accretion disk can be used to probe the feedback mechanism connecting the central black holes with their host galaxies.

CRA Seminar: Ore Gottlieb (Flatiron Institute)
2024-02-15 15:30 - 16:30 | Bogg 1-44 VizLab
Title: Bridging Physics and Observations of Black Hole-Powered Events
Abstract: Black hole (BH)-powered transients are abundant in the Universe, originating from compact object mergers, collapsing stars, galactic cores and more. Upcoming LIGO runs and new electromagnetic detectors, such as LSST and ULTRASAT position BH-powered multi-messenger events at the forefront of astrophysics. I will review the significance of these events in light of the first binary neutron star merger detection, GW170817. One of the primary challenges in studying BH-powered explosions lies in the vast dynamical range between the BH and the emission site, which has hindered theoretical models from elucidating the underlying physics based on observations. I will present the first such models through state-of-the-art simulations that follow outflows from newly formed BHs to the photosphere. I will illustrate how simulations of collapsing stars, which give rise to BHs and relativistic jets, offer unique opportunities to explore a wide range of cutting-edge astrophysical phenomena in an unprecedented manner: heavy element nucleosynthesis, the evolution of relativistic jets, natal properties of BHs, a variety of cosmic fireworks, and predictions of new gravitational wave sources. These predictions will be essential for extracting the physics of transients from future gravitational wave/electromagnetic detections. I will conclude by demonstrating how such models recently enabled us to decipher the origin of the mysterious new class of long gamma-ray bursts associated with kilonovae.

CRA Seminar: Jeremy Perkins (NASA)
2024-02-08 15:30 - 16:30 | Bogg 1-44 VizLab
Title: The Path to a Next Generation Gamma-ray Observatory
Abstract: The Compton Gamma-ray Observatory was a one of the four original NASA Great Observatories and changed our view of the high energy universe. Its successors (INTEGRAL, Swift, and Fermi) have expanded this view and are still contributing in new and exciting ways. There are also many efforts underway in R&D (CZT, pixel detectors, Glowbug, …), ballooning (ComPair, GRAPE, …), SmallSats (BurstCube to StarBurst), missions of opportunity (MoonBEAM, LEAP, …), small explorers (COSI) and medium explorers (AMEGO-X) that are pushing the field forward. The time for planning a new Gamma-ray Observatory is now and I’ll present the scientific case and a path to developing a community backed plan for our next Gamma-ray flagship mission.

CRA Seminar: Songhu Wang (IUB)
2024-02-01 15:30 - 16:30 | Bogg 1-44 VizLab
Title: Exoplanets: Diverse Architectures and Unified Origin
Abstract: While the exoplanetary field is replete with remarkable discoveries, perhaps the two most intriguing findings have been the detection of hot Jupiters – giant planets orbiting perilously close to their parent stars, and the startling abundance of super-Earths – a type of world entirely missing from our solar system. The mere existence of these worlds was wholly unpredicted based on the expectations that were gleaned from centuries of observation of our own solar system. This talk will delve into the demographics and orbital architectures of these exoplanets. We will explore how the sheer variety of observed exoplanetary systems can be reconciled into a unified theoretical framework.

Cosmic Coffee (Howey IZ)
2024-01-31 15:30 - 16:30 | Howey N201/202, 837 State Street, Atlanta, GA, 30332, United States

CRA Seminar: Mehr Un Nisa (MSU)
2024-01-25 15:30 - 16:30 | Bogg 1-44 VizLab

CRA Seminar: Lia Hankla (UM)
2024-01-25 15:30 - 16:30 | Bogg 1-44 VizLab
Title: Kinetic and Two-Temperature Physics of Black Hole Accretion Disks and X-ray Coronae
Abstract: Understanding the plasma physics of accretion disks and coronae around black holes is crucial for interpreting the radiation observed from these systems. However, these plasmas span several different physical regimes. They can be highly collisional and well-described by a single temperature, or collisionless with nonthermal particles that have been accelerated to high energies. My work brings small-scale kinetic and two-temperature physics into the global setting of the accretion disk/corona system. In this talk, I will first build an analytic model using prescriptions from PIC simulations to demonstrate an observable power-law from within the plunging region of a black hole. Next, I use particle-in-cell (PIC) simulations to understand turbulence and particle acceleration in a collisionless, magnetized plasma. Finally, I use general relativistic magnetohydrodynamic (GRMHD) simulations to examine the impact of two-temperature physics on the radial structure of the full accretion disk.

CRA Seminar: Tae Baxter (UCSD)
2023-11-30 15:30 - 16:30 | Bogg 1-44 VizLab

Cosmic Coffee
2023-11-29 15:30 - 16:30, 2023-11-15 15:30 - 16:30, 2023-11-08 15:30 - 16:30, 2023-11-01 15:30 - 16:30, 2023-10-25 08:00 - 17:00, 2023-10-18 15:30 - 16:30 | Howey N201/202, 837 State Street, Atlanta, GA, 30332, United States

CRA -Machine Learning + Astro Seminar : Alec Gunny (MIT)
2023-11-15 12:00 - 13:00 | Howey N201/202, 837 State Street, Atlanta, GA, 30332, United States
Title: Accelerating ML workflows in gravitational wave astronomy
Abstract: Commercial applications of machine learning (ML) have grown substantially in recent years, driven in no small part by an explosion in the ecosystem of so-called MLOps tools that have simplified the development and deployment of common ML use cases using domain-specific best practices. As the canon of ML applications in gravitational wave astronomy proliferates, it is worthwhile to consider what a similar ecosystem, optimized for this unique scientific and computing environment, might look like, and how it might help address the highest-value science goals in the coming years. In this talk, we will discuss some lessons learned from developing a few specific ML applications in this context, and introduce a growing suite of tools designed to encode these lessons and accelerate the pace at which robust, scalable ML applications can be built, tested and put into production.

CRA Seminar: Fred Adams (U. of Michigan)
2023-11-09 15:30 - 16:30 | Bogg 1-44 VizLab

CRA Seminar: Stefanie Milam (NASA Goddard)
2023-11-07 15:30 - 16:30 | Bogg 1-44 VizLab

CRA Seminar: Sarah Vigeland (U. Wisconsin Milwaukee)
2023-10-31 15:30 - 16:30 | Bogg 1-44 VizLab

CRA Seminar: Sreetma Goswami (IceCube)
2023-10-26 15:30 - 16:30 | Bogg 1-44 VizLab

CRA Seminar: Vasilis Paschalidis (U. of Arizona)
2023-10-19 15:30 - 16:30 | Bogg 1-44 VizLab
Title: Magnetohydrodynamic accretion onto binary black holes as a source for multimessenger astronomy with gravitational waves
Abstract: Supermassive black hole binaries can form in magnetized plasma following galaxy mergers, via bar-mode instability in rapidly rotating supermassive stars, or by other dynamical processes. After formation, a combination of dynamical friction and gas-driven migration is likely to catalyze the binary inspiral into the gravitational radiation-driven regime. Following this point, accreting binary black holes become prime targets for multimessenger astronomy with gravitational waves. In this talk we will discuss recent progress in understanding magnetohydrodynamic accretion onto binary black holes. We will focus particularly on variability of the mass accretion rate, Poynting outflows and how the existence of minidisks forming onto the individual black holes may affect observable quantities from these systems.
