Janosz Dewberry

Postdoctoral fellow, CITA

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Welcome! I am a postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics (CITA). As a theoretical astrophysicist with a strong background in fluid dynamics, I use mathematical and numerical tools to tackle a wide variety of problems in astro. Recently, I have focused on the dynamics of stars, gaseous planets, and accretion disks. Read on to find out more about my research:

Rapidly rotating planets and stars

Many stars and gaseous planets spin rapidly; Saturn and Jupiter provide two examples of rapidly rotating, gaseous bodies in our own Solar system. Rapid rotation affects internal structure, flattening the planet or star like a pancake. On top of this distortion, rapid rotation complicates fluid motions caused by, for instance, the perturbing gravitational field of a binary companion star or satellite moon. Many of my current research projects revolve around characterizing the (i) internal structure and (ii) fluid motions of rapid rotators.

Saturn ring seismology

The satellite Cassini confirmed that gravitational perturbations produced by internal oscillations in Saturn drive wave propagation in the planet's rings. Saturn ring seismology provides a rare window into gas giant interiors. Last year, I led a study in which I combined numerical methods developed for dealing with the effects of rapid rotation on stellar oscillations with modern Saturn interior models. More recently, my collaborators and I explored the measurable impacts that rapid differential rotation in Saturn's outer envelope can have on Saturn ring seismology.

Dynamical tidal interactions

Just as the gravitational pull of the moon raises tides on Earth, both Jupiter and Saturn interact tidally with their satellite moons, and stars interact tidally with orbiting planets and/or other stars. This type of gravitational interaction primarily results in a "tidal bulge" that tracks the motion of the perturbing satellite that raised it. Last year, I worked with Professor Dong Lai to characterize the shapes of tidal bulges produced in rapidly rotating planets and stars. In our work, we developed a convenient method for calculating so-called "tidal Love numbers" over a range of rotation rates for simple models relevant to gas giants and some neutron stars.

Accretion disk dynamics

Astrophysical accretion disks are ubiquitous, and essential to many observed astrophysical phenomena. Several processes can distort accretion disks to become eccentric and/or warped. My research in accretion disks mostly revolves around how elliptical streamlines in distorted disks affect the magnetohydrodynamic (MHD) waves and instabilities that govern disk dynamics.

Black hole accretion variability

X-ray binary systems thought to contain accreting black holes occasionally exhibit "high-frequency quasi-periodic oscillations" (HFQPOs) with enigmatic origins. During my PhD, I explored a model for HFQPOs that involves MHD wave excitation by a tidally driven eccentric distortion. I found that the effects of large-scale, mean poloidal magnetic fields on the trapping of these waves may be less destructive than previously thought, especially if the fields are strongly helical. I also used global, nonlinear hydrodynamic and MHD simulations to demonstrate robust wave excitation by eccentric distortions, which in some cases may be strong enough to overcome wave damping by MHD turbulence.