Research

My research in astronomy covers the formation of stars and planets, and primarily studies the dynamical behavior of protoplanetary disks, the large rings of gas and dust surrounding young stars that eventually form into planets. Click on a link below to see some of the specific research topics I am currently working on!

Warped Protoplanetary Disks

Polar Aligned Disks

Protoplanetary Disk Kinematics

Orbits around objects with non-symmetric gravitational fields (such as binary stars) will precess if they have some starting inclination, due to the torque produce from the asymmetry. Around binaries with eccentric orbits, there are two different stable kinds of orbits that a particle can take:

• coplanar orbits, where an orbit precesses around the binary's angular momentum vector.

• polar orbits, where an orbit precesses around the binary's eccentricity vector.

If there are damping forces, like the viscous forces within a disk, then coplanar orbits will settle towards $0^\circ$ inclination, and polar disks settle towards $90^\circ$ inclination. This suggests that there could be an entirely new class of protoplanetary disks unique to binary stars, orbiting perpendicular to the orbits of the parent stars.

To study how a protoplanetary disk would behave in this orientation, we run computer simulations using 3D hyrodynamic codes. A disk in this configuration around a binary could end up forming a planet on a polar orbit around a binary star system, creating a type of exoplanet system never observed before.

Our simulations confirm what previous simulations and theory predict, that disks lining up in this perpendicular fashion undergo a few oscillations on the way there, and settle down faster if the gas in the disk is more viscous. However, if the gas is less viscous, then the gas can undergo the Rossby Wave Instability, creating a dense vortex within the disk. This vortex sends out spiral arms, which can cause matter to accrete onto the central binary stars. This vortex can also concentrate planetesimals into its center, speeding up planet formation and producing polar-aligned planets.

New radio telescopes like the Atacama Large Millimeter Array (ALMA) and the upcoming Next Generation Very Large Array (ngVLA) are allowing astronomers to gain incredibly detailed views into the structure of protoplanetary disks. For the first time, we are able to see the detailed structure within the disk itself, and maybe determine which of these structures are indications of newly forming planets.

Many new images of protoplanetary disks show “gaps” in the material, dark rings where the gas and dust seems to have been removed. There are lots of theories as to why these gaps form, including planets eating up the material in their orbits, material melting from snow lines, and magnetic instabilities. The planet theory is a popular one, but it’s not clear if all of the gaps are caused by planets, since we can’t see any of the maybe-planets that could be in there.

If a planet is orbiting inside the gap, then its gravity will disturb the gas, changing the flow of the material in the regions nearby the planet. This means that, if we study how the gas is flowing in the disk (the gas velocity) as well as where it is located (the gas density), we can pin down the location and properties of any potential planets!

Using hydrodynamic simulations, we were able to find that different features of the disk can be highlighted by different velocity components. Material moving directly towards or away from the central star tends to follow the spiral wave generated by the planet, whereas material moving slower or faster than normal Keplerian speed tends to follow the edges of the gap. Emission channel maps from ALMA can be used to identify these features and pinpoint the location of an embedded planet!