Astrophysics & Planetary Sciences Colloquium

A surprising discovery has been compact systems of Earth to super- Earth-sized planets. While compact systems are common, their origin is debated. A prevalent assumption is that compact systems formed after the infall of gas and solids to the circumstellar disk ended. However, observational evidence suggests accretion may commence earlier. We propose that compact systems are surviving remnants of planet accretion during the end stages of infall.

Abstract: The discovery of thousands of planets orbiting stars beyond the solar system has fundamentally shifted our view of Earth’s place in the Universe, has captivated the public imagination, and has transformed research priorities in astrophysics. We are now actively searching for atmospheres on temperate, terrestrial planets, and are developing the technical tools to find and characterize “Earth-2.0”.

Abstract: This talk will explore how quantum radiation - known as Hawking radiation – emerges when a black hole forms in the gravitational collapse of a star. While it has long been known that black holes emit energy, its precise origin has been debated. Over the decades, some researchers proposed that this energy is released directly from the collapsing star, producing a sudden burst that may potentially disrupt the collapse.

Abstract: The scales of asteroid strength, from centimeters to tens of meters or more, can in principle be connected via the well-known Weibull theory (Weibull 1951) that explains in probabilistic terms why small samples of a rock are stronger than the whole. There are fewer weak flaws to be exploited in a smaller sample. This leads to a statistical understanding of size-dependent strength that has been implemented in fragmentation and damage models for planetary materials (Melosh et al., 1992; Benz and Asphaug 1994, 1995). The Weibull analysis enabled Cotto-Figueroa et al.

The corona is a layer of hot plasma that surrounds the Sun, traces out its complex magnetic field, and ultimately expands into interplanetary space as the supersonic solar wind. This complex and unpredictable system varies over many orders of magnitude in space and time, so it's not surprising that we still do not have a complete theoretical understanding of its origins. In this talk, I will present some new observations and theoretical concepts that are helping us get closer to finally identifying and characterizing the physical processes responsible for the corona and solar wind.

The Hubble Space Telescope story has been a fascinating study in public policy, engineering, ethics, and science. The Hubble is perhaps the most productive scientific instrument ever created by humans. In May 2009, a team of astronauts flew to the Hubble Space Telescope on space shuttle Atlantis. On their 13-day mission and over the course of 5 spacewalks they completed an extreme makeover of the orbiting observatory.

The launch and commissioning of the James Webb Space Telescope is ushering in a new era in our understanding of our cosmic origins. Galaxies are a fundamental building block of the universe, yet how they formed has remained enigmatic owing to our inability to observe them at early cosmic times. In just its first three years of operation, JWST has already upended our understanding of galaxy and black hole growth in the early universe.

Parker Solar Probe successfully completed its prime mission in 2025, measuring solar wind plasma in-situ as close as 8.8 solar radii (~0.04 AU) from the solar photosphere over a series of close-approach orbits. These close approaches to the Sun enable novel exploration of fundamental stellar processes, such as solar wind acceleration, solar wind heating, interplanetary dust destruction, and radial evolution of solar surface structure. These processes leave distinct signatures in near-Sun particle and field observations that allow us to untangle the physical mechanisms driving them.

The availability of exascale computing resources has enabled numerical modeling of astrophysical fluid dynamics at unprecedented scale, including studies of MHD turbulence on grids with 10,000^{3} cells, or MHD models of black hole accretion in full GR with radiation transport. Results from a diverse range of applications will be presented, including new insights into the structure of radiation-dominated accretion disks, modeling AGN feedback in elliptical galaxies, and turbulence and cosmic ray transport in the interstellar medium.

How big would Mercury need to be to retain an atmosphere? How close could Venus orbit the Sun before its atmosphere erodes away? Are habitable Earth-like atmospheres even possible around the smallest stars? In this talk, I describe how exoplanet observations are starting to provide insight on what environments permit terrestrial planet atmospheres to thrive.