List of Past Astronomy Colloquia : 01-Sep-2011 to 31-Dec-2011

Date:   Wednesday 07-Sep-2011
Speaker:   Dr. Derek Richardson (University of Maryland)
Title:  "Weak Forces on Small Bodies in the Solar System"

Comet breakups, the existence of asteroid families and satellites, and even the properties of light scattered from Saturn's main rings have led to a better appreciation for the role of weak forces in the evolution of small solar system bodies. Once thought too weak to be important, it is now evident that fragments of small bodies can reassemble after catastrophic disruption through the action of gravity alone. This gravitational reaccumulation explains the morphology of the fragments of Comet Shoemaker-Levy 9 following its breakup at Jupiter, the size and velocity distribution of main-belt asteroid families, the shape and spin distribution of small-to-medium-size asteroids, and the formation of small-body satellites. It is also consistent with the low bulk densities (less than 3 g/cc) and implied large porosities of several asteroids visited by spacecraft, including tiny Itokawa. Over much longer timescales, the action of sunlight (besides triggering outgassing on comets) can alter the orbits and spins of asteroids. In fact, it may be possible for near-Earth asteroids to be spun up by the thermal YORP effect to the point that they shed mass, reshape, and form satellites. Recently, the presence of regolith (inferred from thermal inertia measurements) on even small, fast-spinning asteroids suggests that weak cohesive forces, such as van der Waals bonding, may be important for the evolution of their surfaces. Cohesion may also play a role in the dynamics of Saturn's main ring particles. In this talk, I will review the substantial progress that has been made in understanding and simulating weak forces on small bodies in the solar system. Planned and future space missions, possibly leading to astronauts visiting a near-Earth asteroid, motivate even more detailed studies, including experiments and simulations of granular flow in very low gravity. I will present preliminary progress in these areas.

Date:   Wednesday 14-Sep-2011
Speaker:   Dr. Christopher McKee (UC Berkeley)
Title:  "The Formation of Massive Stars"

Date:   Wednesday 21-Sep-2011
Speaker:   Dr. Alberto Bolatto (University of Maryland)
Title:  The Large Scale Picture of Star Formation in Galaxies; Bright Gas, Dark Gas, and Galaxy Evolution

Recent observations have shown that "normal" galaxies evolve mostly not through major mergers (although those produce some truly spectacular examples) but via a combination of cold mode accretion and star formation. In this colloquium I will discuss some of our efforts to better understand the relation between gas and star formation in galaxies at present times, and throughout cosmic history.

Date:   Wednesday 28-Sep-2011
Title:  N/A

Date:   Wednesday 05-Oct-2011
Speaker:   Dr. Meg Urry (Yale University)
Title:  Women in Science: Why So few?

Many people agree there are too few women and minorities in science but disagree about why, and what to do about it. Fortunately, social science research has addressed this issue extensively. I will review some gender statistics in different STEM (science, engineering, math and technology) fields, highlighting differences in critical points along the career path. I then describe some of the social science experiments, especially those relating to unconscious bias, and show how their results pertain to minority groups in science. I conclude with a set of steps for improving gender equity in STEM fields.

Date:   Wednesday 12-Oct-2011
Speaker:   Dr. Maxim Markevitch (NASA/GSFC)
Title:  "Intergalactic Shock Fronts"

Mergers of galaxy clusters -- some of the most energetic events in the Universe -- produce disturbances in hot intracluster medium, such as shocks and cold fronts, that can be used as tools to study the physics of galaxy clusters. X-ray observations of shock fronts provide information on the shock Mach number and velocity, and for well-observed shocks, constrain the microphysical properties of the intracluster plasma. Cold fronts may constrain viscosity and the structure and strength of the cluster magnetic fields. Combined with radio data, these observations also shed light on the production of ultrarelativistic particles that are known to coexist with the cluster thermal plasma. While cold fronts are commonly seen in merging and relaxed clusters, only a few unambiguous shock fronts have been seen in X-rays so far. This talk will summarize the current X-ray observations of cluster mergers, as well as some recent radio data and high-resolution hydrodynamic simulations.

Date:   Wednesday 19-Oct-2011
Speaker:   Dr. Rachel Ivie (American Institute of Physics)
Title:  Facts and Figures on Astronomy Education and Employment

The academic year ending in 2010 set several records in astronomy. During this year, the numbers of people taking introductory astronomy, earning bachelorís degrees in astronomy, and attending graduate school in astronomy reached all-time highs. The number of people earning PhDs in astronomy and the percentage of these degrees earned by women continues to increase. In this talk, I will present statistics on the latest trends in physics and astronomy degrees and employment. I will highlight trends for women and under-represented minorities. Finally, I will describe the goals of and some initial findings from the longitudinal study of astronomy graduate students.

Date:   Wednesday 26-Oct-2011
Speaker:   Dr. James Jackson (Boston University)
Title:  The Millimeter Astronomy Legacy Team 90 GHz Survey (MALT 90)

I present results from the first year of the MALT 90 Survey, a multi-line survey of molecular emission from dense, high-mass star-forming cores. MALT90 uses the Mopra 22-m telescope in Australia to map 16 molecular lines simultaneously toward a sample of dense cores identified by the 870 micron ATLASGAL continuum survey. I will describe three early results from the first yearís survey data of 500 cores: (1) a technique to find distances and Galactic structure, (2) the discovery of greatly varying chemical composition and its relation to core evolution, and (3) the extension of the Gao and Solomon relation between molecular line and infrared luminosity, first established for galaxies, to the scale of individual cores.

Date:   Wednesday 02-Nov-2011
Speaker:   Dr. Matthew Hedman (Cornell)
Title:  What's going on around Saturn: Rings science from the Cassini mission.

For the last seven years, the Cassini spacecraft has been in orbit around Saturn, making a wide variety of measurements of the planet, its moons and its rings and providing abundant new information about the diverse range of dynamical phenomena occurring in this complex system. In particular, Saturn's diverse rings provide an unique opportunity to investigate the physical processes operating in these nearby astrophysical disks at high resolution and in great detail. For example, Cassini data is finally allowing us to probe the structure and dynamics of the densest regions in Saturn's main rings, which are nearly opaque and have been extremely difficult to theoretically analyze or numerically simulate. Meanwhile, Saturn's dusty faint rings contain puzzling asymmetric structures that appear to be aligned with the sun and are therefore likely generated by non-gravitational forces like solar radiation pressure. Finally, some features in the rings even seem to be echoes of discrete events like cometary impacts that occurred decades before Cassini reached Saturn, and can therefore be used to trace the recent history of the Saturn system.

Date:   Wednesday 09-Nov-2011
Speaker:   Dr. Kayhan Gultekin (University of Michigan)
Title:  Black Hole Scaling Relations: Smoking Gun or Red Herring?

It has been over a decade since the discovery that the mass of a central black hole scales with the properties of its host galaxy. Because of these remarkable scaling relations, the idea that galaxies and black holes coevolve through some sort of self-regulated feedback has come to dominate scientific discussion. But do we really understand what the scaling relations are telling us? Since the original scaling measurements, the total number of supermassive black holes with direct mass measurements has reached 50. I will present recent developments from the observational perspective of the black hole scaling relations and how well coevolution models can handle this. In addition to coevolution, the scaling relations in the local universe inform the study of formation of black hole seeds, black hole density functions across cosmic time, and the disputed claims of evolution of the scaling relations with redshift. I will also explore what important, observational questions still need to be answered.

Date:   Wednesday 16-Nov-2011
Speaker:   Dr. Richard Walker (University of Maryland)
Title:  Nebular mixing as deduced from high precision isotopic analysis of bulk planetary materials: New tool in the study of late stage planetary accretion?

High precision mass spectrometry has revealed that the isotopic compositions of some elements, such as Sm, Nd, W, Ru and Mo, vary among early-formed planetesimals. These variations likely reflect incorporation of different proportions of matter from diverse nucleosynthetic sources, and could be the result of accretion from a poorly mixed nebula, accretionary processes that favored isotopically distinct components, and/or late injection of isotopically diverse matter to the nascent Solar System. Constraints placed on the level of isotopic variability among early-formed planetesimals for additional elements with different chemical characteristics and nucleosynthetic origins may help to elucidate the dominant processes. The nature of the isotopic anomalies present in the diverse components of primitive meteorites, as well as in meteorites that may sample the bulk compositions of individual planetesimals will be discussed. The genetic fingerprints the isotopic anomalies provide for some elements may be used to distinguish the origins of late accreted materials to the terrestrial planets.

Date:   Wednesday 23-Nov-2011

Date:   Wednesday 30-Nov-2011
Speaker:   Dr. Larry Nittler (Carnegie Institute of Washington)
Title:  Hermeochemistry: The composition of Mercury from MESSENGER X-ray, Gamma-ray, and neutron measurements

Elemental abundances at the surface of a rocky planet reflect both the original composition of the body and the various processes that have shaped the surface over billions of years. NASA's MESSENGER spacecraft has been in orbit around Mercury since 18 March 2011, and contains X-ray, Gamma-ray and neutron spectrometers designed to characterize the chemical composition of the planetís surface. Initial results indicate a planetary surface formed by significant partial melting of a highly chemically reduced, but not highly volatile depleted, silicate mantle. Implications for models of Mercury's origin and evolution will be discussed.

Date:   Wednesday 07-Dec-2011
Speaker:   Dr. Jane Rigby (NASA/GSFC)
Title:  "Watching Galaxy Evolution in High Definition".

As Einstein predicted, mass deflects light. In hundreds of known cases, "gravitational lenses" have deflected, distorted, and amplified images of galaxies or quasars behind them. As such, gravitational lensing is a way to "cheat" at studying how galaxies evolve, because lensing can magnify galaxies by factors of 10--100 times, transforming them from objects we can barely detect to bright objects we can study in detail. I'll summarize new results from a comprehensive program, using multi-wavelength, high-quality spectroscopy, to study how galaxies formed stars at redshifts of 1--3, the epoch when most of the Universe's stars were formed.

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