Description:

Dynamics and Collisional Evolution of Closely Packed Planetary Systems

Jason Hwang

High-multiplicity Kepler systems (referred to as Kepler Multis) are often tightly packed and may be on the verge of instability. Many systems of this type could have experienced past instabilities, where the compact orbits make physical collisions likely outcomes. We focus specifically on systems resembling Kepler-11, a Kepler Multi with six planets, and run a suite of dynamical integrations, sampling the initial orbital parameters around the nominal values reported in Lissauer et al. (2011). We examine the characteristics of each planet-planet collision, categorizing collisions by the degree of contact and collisional energy, and find that grazing collisions are more common than direct impacts. Since the structure of many planets found in Kepler Multis is such that the mass is dominated by a rocky core, but the volume is dominated by a low-density gaseous envelope, the sticky-sphere approximation may not be valid, and we present hydrodynamic calculations of planet-planet collisions clearly deviating from this approximation.

Distinguishing Between Formation Channels for Binary Black Holes with LISA

Katie Breivik

The recent detections of GW150914 and GW151226 imply an abundance of stellar-mass binary black hole (BBH) mergers in the local universe. While ground-based gravitational wave detectors are limited to observing the final moments before a binary merges, space-based detectors, such as the Laser Interferometer Space Antenna (LISA), can observe binaries at lower orbital frequencies where such systems may still encode information about their formation histories. In particular, the orbital eccentricity and mass of BBHs in the LISA frequency band can be used together to discriminate between binaries formed in isolation in galactic fields and those formed in dense stellar environments such as globular clusters. In this talk, I will describe the orbital eccentricity and mass of both BBH populations as they evolve through the LISA band and show how LISA may be able discern which BBHs originated from each formation channel.