Two Speakers: Margaret Pan (MIT) and Suoqing Ji (University of California, Santa Barbara)
Where are the resonant exoplanet pairs?
Speaker: Margaret Pan, MIT
Of the ~1400 exoplanets now known to reside in multiple planet systems, the vast majority do not lie in or near mean motion resonances. This appears to contradict the established wisdom that pairs of planets undergoing convergent migration due to disk-planet interactions should efficiently capture into resonance. Several explanations have been proposed for this, including escape from resonance due to overstable librations or disk turbulence; inefficient capture due to eccentricity excitation by disk warps; or even a complete absence of migration, i.e. in situ formation. I will discuss another possibility: smaller overall resonance capture probabilities for smaller planets and gravitational stirring among neighboring planets can conspire to make resonant planet pairs unlikely around solar-type stars but more likely in M dwarf systems.
Make it, Mix it and Shake it — a recipe for cold gas in circumgalactic medium
Speaker: Suoqing Ji, University of California, Santa Barbara
Multiphase gas structure is ubiquitous in our universe. Recent observations suggest that large quantities of cold gas with temperature of a few 10^4 K are found in circumgalactic medium (CGM), which extends up to a few times of galactic virial radius. However, the origin and fate of such cold gas still remain unclear. In this talk, I will mainly explore magnetized thermal instability as a promising mechanism for cold gas formation. In addition, I will discuss warm gas generation from MHD turbulent mixing layers, and preliminary particle-fluid simulations of cold cloudlets, which paves the way for final two-fluid model of cold gas in cosmological simulations. (P.S. A number of artistic fridge magnets will be distributed as small gifts at the seminar.)