Binary Galaxy Merger
with Patrik Jonsson and Joel Primack. The visualization uses Sunrise, a Monte-Carlo radiative transfer code written by Patrik Jonsson that calculates what galaxies would actually look like given their star formation histories and the distribution of gas and dust in the galaxy. The animation is also available on YouTube, where it's currently the first result when you search for "Galaxy Merger"!
These animations show black hole fueling and feedback in an elliptical galaxy. The simulations assume axisymmetry. Note carefully that the radial coordinate is the log of the radius! This allows you to see fine detail near the center (resolution 0.1 parsec) as well as dynamics taking place at galactic scales (kiloparsecs). You will notice that the dynamical times near the center are much shorter than those further out in the galaxy. You can see cold blobs of gas generated at ~1 kpc by cooling instabilities falling to the center, followed by heating and outflows as that gas falls into the black hole. The panels show the gas density, sound speed (temperature), pressure, and the three components of the velocity. This work was done in collaboration with Jeremiah Ostriker and Luca Ciotti.
MHD Simulations of AGN in a Galaxy Cluster
These are magneto-hydrodynamic simulations of the consequences of a black hole generating a magnetic field at the center of a galaxy cluster. Pressure from the magnetic field creates a bubble that buoyantly rises through the gas in the cluster. This work was done in collaboration with Renyue Cen.
These show the decay of turbulent motions in the cluster gas in the absence of a mechanism to drive the turbulence.
Galaxy Merger Simulations
These galaxy merger simulations are designed to better understand how large, spherical, slowly rotating elliptical galaxies were formed. This work was done in collaboration with Joel Primack, Patrik Jonsson, and TJ Cox.
Multiple mergers in binary pairs
Multiple mergers, one after another sequentially
Cosmological initial conditions (1)
Cosmological initial conditions (2)
Cosmological initial conditions (3)
Co-orbital resonance in Planet Systems
Presented at the Division on Dynamical Astronomy meeting April 2002
There are many stable resonances where the two orbiting planets have the same semi-major axes and therefore the same orbital periods. Trojan, tadpole, and horseshoe orbits are the best known, but there are also retrograde satellite orbits. I studied the dynamics of the retrograde satellite orbits where both of the orbiting bodies have non-zero mass and therefore have very interesting interactions. In particular, the resonance is stable up to very high eccentricities where the two planets undergo a close approach every orbit. However, the close approach is perfectly timed so that the interaction between the planets keeps them from suffering a catastrophic collision. Instead, they engage in a precisely choreographed dance where they exchange angular momentum over the course of several hundred orbits.
We were interested in these configurations of planets because they are very difficult to detect in radial velocity surveys since both planets are contributing to the signal with the same period.
To give you a clear idea of what happens, this is an animation of the full secular cycle. It's not terribly exciting, but if you have a lot of patience you'll see that the two planets do a full exchange of angular momentum: the initially eccentric orbit becomes circular and the initially circular orbit becomes eccentric.
It is much easier to understand the dynamics of the system if you instead make an animation where you "strobe" it at the point where one of the planets is at the first orbit crossing point or the second orbit crossing point. Each frame of the "strobed" animations is a snapshot of the system at the moment when one of the two planets is at the orbit crossing point, so that there's only one animation frame per orbit. Download the PDF of my talk at the meeting.
This work was done in collaboration with Greg Laughlin.