Astrophysics and Relativity Seminars

Cosmological models are informed by observations of the Cosmic Microwave Background and distant galaxies. However, these leave much of the volume of the observable universe unexplored, meaning that key epochs in cosmic history are unconstrained. In particular, we have limited observational evidence of the Cosmic Dawn, when stars and galaxies first formed, and the Epoch of Reionization (EoR), when early stars and galaxies ionized the surrounding intergalactic medium. We also lack detailed measurements of the universe’s large-scale structure at near redshift. I will discuss how interferometric radio telescopes can fill in these gaps. Using the 21 cm emission line from neutral hydrogen, these telescopes can map enormous volumes of the universe, answering questions about the origins and evolution of our modern universe. I will present recent progress constraining models of early galaxy formation with 21 cm intensity mapping and discuss how next generation experiments like the DSA-2000 will deliver on the promise of 21 cm cosmology.

Galaxies lie at the nexus of modern astrophysics—serving as essential cosmological probes, while setting the environment in which stars form and compact objects merge. Yet, despite their central role, the physics governing their evolution remains elusive. The key lies in deciphering the intricate balance between inflows and outflows that shape galaxies and regulate the fuel supply for star formation and black hole growth. In this talk, I will describe my efforts to forge a robust framework that self-consistently captures the governing processes across a daunting range of scales by combining state-of-the-art simulations, intuitive analytic models, and novel numerical methods. I will show how micro-scale (~sub-pc) processes, such as cosmic ray transport, magnetic reconnection, and turbulent mixing, connect with meso-scale (~kpc) phenomena, such as supernova-driven galactic winds, and how—when combined using innovative multi-scale techniques—they shape the macro-scale (~Mpc) dynamics and galactic properties. This approach bridges not only scales but also diverse disciplines—from fluid dynamics and plasma physics to cosmology, with insights drawn from climate modeling and pure mathematics. Taken together, these efforts aim to reshape our interpretation of observations and usher in a new era of truly predictive galaxy modeling built on a foundation of solid physical principles.

The first Event Horizon Telescope images of the supermassive black hole M87* display a bright ring encircling the event horizon, which appears as a dark patch in its surrounding emission. But Einstein's theory of general relativity predicts that within these images there also lies a thin “photon ring” of light that orbited the black hole before escaping its gravity, carrying information about its spacetime properties and, in particular, its spin. I will describe a NASA Small Explorers Mission being proposed this year: the Black Hole Explorer. BHEX will use space-ground interferometry to create a telescope larger than the Earth and produce the sharpest images in the history of astronomy. By resolving the photon ring, these images will address fundamental questions in black hole physics, including what a black hole looks like, and how fast the black hole Sgr A* at the center of our own galaxy is spinning. BHEX will also target dozens of additional supermassive black holes and measure the magnetic fields suspected to generate their relativistic jets, shedding new light on the mechanism that powers the brightest and most efficient engines in the universe.

Today, modern telescopes, planetary science missions, and gravitational wave experiments are collecting a large volume of precise data. Insights from these data are in turn accelerating advances toward accurate and efficient fluid dynamical models of stellar and planetary systems. For example, seismic waves in Saturn’s rings are changing our understanding of giant planets. Tides raised in Jupiter and Saturn similarly tell us about these planets’ structure and dynamics. Outside of our solar system, the interactions of exoplanets and stars both with each other and with their environments leave imprints in astronomical survey data. In this talk, I will describe research focused on developing improved, multidimensional models of planets, stars, and their environments that rise to the challenge and opportunity presented by modern astronomical observations.