CGCA Seminars

Dr. Amy Steele, Planetary Science Institute The CGCA Friday Seminar Series is hosted by the Center for Gravitation, Cosmology & Astrophysics at the University of Wisconsin-Milwaukee. These seminars cover a broad number of topics related to the Center's research areas. …

Self-Consistent Simulations of the Bar-mode Instability in Rotating Quasi-Stable Neutron Stars
Dr. Terrence Pierre Jacques
West Virginia University

Rapidly rotating neutron stars (NSs) formed from core-collapse supernovae serve as excellent astrophysical laboratories for probing their equation of state (EoS) and internal structure. As these stars cool and contract, their spin angular momentum may increase, making them susceptible to the dynamical bar-mode instability

The masses and radii of the neutron stars observed by NICER
Prof. Sharon Morsink
University of Alberta

Neutron stars are the densest known gravitationally-stable objects in the Universe. Their strong gravitational fields, rapid rotation rates, and supra-nuclear central densities allow for a fascinating interplay between general relativistic effects and nuclear physics theory. Pulse-profile modeling is a technique that uses the gravitationally-lensed X-ray flux emitted from hot spots on the neutron star's surface to infer its mass and radius. General relativity is a crucial ingredient in this analysis.

Frame-Dragging Reveals Central Engine of a Superluminous Supernova
Dr. Logan Prust
Center for Computational Astrophysics - Simons Foundation

Type I superluminous supernovae (SLSNe-I) are an order of magnitude brighter than standard supernovae, with the internal power source for their luminosity still unknown. The central engines of SLSNe-I are hypothesized to be magnetars, but many SLSNe-I light curves exhibit multiple bumps or peaks that are unexplained by the standard magnetar model.

Can black holes evaporate past extremality?
Professor Samuel E. Gralla
University of Arizona

Black holes with sufficiently large initial charge and mass will Hawking-evaporate towards the extremal limit. The emission slows as the temperature approaches zero, but still reaches the point where a single Hawking quantum would make the object superextremal, removing the horizon. We take this semiclassical prediction at face value and ask: When the emission occurs, what is revealed?

What’s Feeding Terrestrial Planets? JWST Observations of Protoplanetary Disk
Dr. Abygail Waggoner
University of Wisconsin-Madison

The formation of terrestrial, or earth-like, planets is thought to occur in the inner few au of protoplanetary disks, but what is the composition of the dust and gas that forming-planets may inherit? In this talk, we’ll discuss how the James Webb Space Telescope can be used to measure the chemical composition of protoplanetary disk gas and how models can be used to understand the evolution of material throughout planet formation.

Detecting Gravitational Wave Signals - Methods, Challenges, and Opportunities
Shio Sakon
Pennsylvania State University

The LIGO-Virgo-KAGRA Collaboration’s fourth observing run (O4) produced a remarkable expansion of the gravitational-wave transient catalog, with nearly three times as many significant detections as were known at the start of the run. Among these were several first-of-their-kind events that challenged existing theories, and the increased rate of detections reflected the improvement in detector sensitivity and analysis capabilities over the past decade.

Neutron Star–Black Hole Binaries: Predictions and Observations
Debatri Chattopadhyay
Northwestern University

Neutron star–black hole (NS–BH) binaries have emerged as key targets for multi-messenger astrophysics following the first gravitational wave detections of such systems. In this talk, I present population synthesis predictions for the Galactic NS–BH population, models that interpret the first observed mergers, and forecasts for future radio, gravitational-wave, and electromagnetic discoveries.

Unraveling the origins of fast radio bursts and using them as probes of extreme plasmas
Kenzie Nimmo
Northwestern University

Fast radio bursts (FRBs) are millisecond-duration flashes of coherent radio emission originating from extragalactic distances, offering a unique view into the physics of compact objects and their surrounding environments. Despite their brief and unpredictable nature, precise localizations of a small number of FRBs have already revealed a striking diversity in host galaxies, local environments, and burst properties - suggesting multiple progenitor channels linked to extreme compact objects. However, the nature of FRB sources remains one of the most exciting mysteries in astrophysics.

Black Holes: Bridging Simulations and Observations
León Salas
University of Wisconsin-Milwaukee

In recent years, General Relativistic Magnetohydrodynamic (GRMHD) simulations, combined with multiwavelength observations have provided critical insights into the nature of radiation from accreting black holes. These simulations have revealed a particularly interesting magnetically arrested disk (MAD) regime whereby the accretion is choked by strong magnetic fields. The higher magnetic flux characteristic of the MAD regime leads to new dynamics, including interchange-type accretion modes and flux eruptions. Polarization measurements by the Event Horizon Telescope (EHT) from the supermassive black holes M87* and Sagittarius A* (Sgr A*) favor MAD states. However, nearly all MAD models exhibit greater 230 GHz flux variability than seen in historical observations of Sgr A*.