Research

Accretion-Flow Spiral Waves

Plasma that is falling into a black hole can develop spiral-shaped waves, which likely influence how the black hole's surroundings appear to telescopes. In this project, we investigated how these waves behave when the plasma is sufficiently hot that particles are unable to collide with one another. We found that microscopic instabilities in the plasma can produce a surprisingly strong damping effect, weakening the spiral waves and slowing their motion around the black hole. Our results may help explain why the black hole at the center of our galaxy, Sagittarius A*, flickers less than computer simulations predict, and could improve our interpretation of future movies from the Event Horizon Telescope.

White Dwarf Natal Kicks

When stars like our Sun reach the end of their lives, they shed their outer layers and leave behind dense stellar remnants called white dwarfs. This mass loss can give the star a series of small, randomly directed pushes, or "kicks," which can significantly alter the orbits of nearby stars and planets. In this project, we developed a mathematical model describing how these kicks accumulate over time as a random walk, and show that it can explain several puzzling features of observed binary star systems. Our results also have implications for the fate of planetary systems like our own, including how asteroids and comets might be ejected into interstellar space.

Viscosity in the Intracluster Medium

The plasma that permeates the space in between galaxies in galaxy clusters - known as the intracluster medium - is frequently stirred up by mergers with other clusters and outflows from the nuclei of galaxies contained within. These processes are understood to drive turbulence, which facilitates the movement of energy between flows at different scales. However this plasma is also expected to be very viscous, which implies that the swirling turbulent flows cannot cascade to much smaller scales before they are dissipated. In this project, we are investigating how the plasma self-organizes, through a process known as "magneto-immutability", to avoid the motions that are most susceptible to viscosity. As a result, we anticipate that these fluctuations can span from hundreds of kiloparsecs, all the way down to the scale of planets!

Collisionless waves

Wave dynamics is one of the most fundamental aspects of how a plasma evolves. Much progress has been made in turbulence by understanding the kinds of waves present in a plasma and how they interact to move energy between scales. In many astrophysical plasmas, these waves are affected by individual particle effects such as damping from resonant wave-particle interactions or small-scale instabilities. We studied the importance of these effects in compressive waves, to better understand their role in turbulent plasmas like those seen around black holes or in galaxy clusters.

Statistical models of the plasmoid instability

Magnetic reconnection is a phenomenon by which significantly strained magnetic field lines suddenly release large amounts of energy into the surrounding plasma, breaking and snapping together in such a way that they reach a much more relaxed state. Various models have aimed to explain how this reconnection can happen in a sufficiently rapid manner that explains observations of energy release in events like coronal mass ejections. One such model focuses on a process called the plasmoid instability, which speeds up this reconnection by creating numerous magnetic islands, each of which drive reconnection at many different sites (sort of like how a parallel computing task can be completed faster than a serial one). We investigated the changes that would occur to the long-time limit behavior of this instability when another component of the magnetic field is added to the process, one which doesn't partake in the reconnection itself (known as a guide field).

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