New Frontiers in Cosmology

Cosmological observations have provided us with answers to age-old questions, involving the age, geometry, and composition of the universe. However, there are profound questions that still remain unanswered. I will describe ongoing efforts to shed light on some of these questions. In the first part of this talk, I will explain how we can use measurements of the CMB and the large-scale structure of the universe to reconstruct the detailed physics of much earlier epochs, when the universe was only a tiny fraction of a second old.

The new phase space complexity of old globular clusters

Our traditional interpretative picture of the internal dynamics of globular clusters has been recently revolutionized by a series of discoveries about their chemical, structural, and kinematic properties. The empirical evidence that their velocity space is much more complex than usually expected encourages us to use them as refreshingly novel phase space laboratories for some long-forgotten aspects of collisional gravitational dynamics.

(Special date) The Troubled Puberty of the Solar System

When the Solar System was formed in a young star cluster a nearby star might have exploded in a supernova. The repercussions of such an event can be rather profound, and the current Solar system may still bear the memory of this traumatic event. The truncation of the Kuiper belt and the tilt of the ecliptic plane with respect to the Sun's rotation axis could be such signatures.

(Special date; 2 pm) The Evection Resonance: A Resurrection in Three Movements

The Evection is a "regular variation in the eccentricity of the Moon's orbit around the Earth, caused mainly by the Sun's attraction" (O.E.D.). It is the signature of a now weakened resonance between the period of apse precession of the lunar orbit and the year. Kinematically "epicycled" by Ptolemy and followers, it proved a source of headaches to Newton, anxious as he was to deploy his newly forged arsenal on the preeminent three-body problem of Sun, Earth and Moon.

(Special date) Kepler's Multiple Planet Systems

More than one-third of the more than 4000 planet candidates found by NASA’s Kepler spacecraft are associated with target stars that have more than one planet candidate, and such “multis” account for the majority of candidates that have been verified as true planets. The large number of multis tells us that flat multiplanet systems like our Solar System are common. Virtually all of the candidate planetary systems are stable, as tested by numerical integrations that assume a physically motivated mass-radius relationship.

Convection in Cool Stars, as Revealed through Stellar Brightness and Radial Velocity Variations

As a result of the high precision and cadence of surveys like MOST, CoRoT, and Kepler, we may now directly observe the very low-level light variations arising from stellar granulation in cool stars. Here, we discuss how this enables us to more accurately determine the physical properties of Sun-like stars, to understand the nature of surface convection and its connection to magnetic activity, and to better determine the properties of planets around cool stars.

On the Origin of the Magic Scale of Galaxies

This talk will address the preferred mass and time for galaxy formation, in dark-matter haloes similar to that of the Milky way but when the Universe was a few Gigayears old. It is proposed that this is due to the interplay between two mechanisms, first supernova feedback that removes gas from the galaxy, and second hot gas in the deep potential well of massive haloes that suppresses cold gas supply to the galaxy, the two being effective in galaxies of lower and higher masses respectively.

Tidal Disruption Events: Accretion Flows Doing What They Shouldn't

Although rare, tidal disruption events, the dismemberment of a star by a massive black hole, are now observable. These events provide a special window on accretion dynamics because they violate many of the standard assumptions: they are intrinsically transient, the fluid orbits are far from circular, the density distribution is strongly asymmetric, the mass accretion rate can be substantially super-Eddington, and shocks are important to both angular momentum transport and orbital energy dissipation.

Distances to Gaia Stars

Gaia will eventually generate astrometric information, including parallax, for 2 billion stars. A lot of these distance estimates will be very noisy. I will talk about our work on using data-driven models to make these distance estimates more precise, to help improve Gaia's general goals of mapping out structures in the Milky Way.