List of Past Astronomy Colloquia : 01-Sep-2013 to 31-Dec-2013

Date:   Wednesday 11-Sep-2013
Speaker:   Prof. Joe Silk (Johns Hopkins University/Univ.& Inst. d'Astrophysique de Paris)
Title:  The AGN-Star Formation Connection

I will review our understanding of star formation feedback. I will focus on the formation of massive spheroids, where one invariably finds evidence for the presence of supermassive black holes. These are often visible, especially at early epochs, as active galactic nuclei. Negative feedback, from the central black hole during its accretion phase, quenches the gas supply to the spheroid and thereby suppresses star formation. We also observe enhanced star formation at early epochs. I will review the various theoretical and observational implications of the AGN-star formation connection.

Date:   Wednesday 18-Sep-2013
Speaker:   Prof. Humberto Campins (University of Central Florida)
Title:  Water and Organic Molecules on Asteroids and on Earth

The detection of water ice and organic molecules on of asteroids 24 Themis and 65 Cybele were reported in 2010 and 2011, respectively. Infrared spectra of these asteroids indicate that the ice and organics are widespread on their surfaces. These discoveries have important implications on current views of primitive asteroids, the delivery of water and organic molecules to Earth, and the origin and evolution of life on Earth. They are also very relevant to three asteroid sample return missions: NASA's OSIRIS-REx, JAXA's Hayabusa 2, and ESA's Marco Polo-R.

Date:   Wednesday 25-Sep-2013
Speaker:   Dr. Eileen Meyer (Space Telescope Science Institute)
Title:  The Near and Far Sides of M87: Proper Motion Measurements of the Optical Synchrotron Jet, Counterjet, and Nuclear Regions

Using over 13 years of archival HST observations of the relativistic jet in the archetypal radio galaxy M87, we have produced astrometric speed measurements of the optically bright synchrotron emitting plasma components in the jet with unprecedented accuracy. Building on previous work showing the superluminal nature of the jet in the optical, we have found that the jet motion is incredibly complex, with both transverse motions and flux variations which can be seen by the naked eye in the timeseries of deep exposures. These observations of M87 provide us with a unique dataset with which to refine theoretical models of the largescale jet structure, potentially addressing open questions such as the jet collimation mechanism, bulk acceleration and deceleration in the jet, and the presence of a helical structure. I will also present very recent results using data from the HST archive on the optical counterjet and nuclear regions of M87 and discuss the larger implications of these detailed studies of one of the most nearby AGN jets.

Date:   Wednesday 02-Oct-2013
Speaker:   Prof. Lucy Fortson (University of Minnesota)
Title:  Citizen Science: Getting the Best Science from Big Data

Citizen science - the involvement of hundreds of thousands of people in the research process - provides a radical solution to the challenge of dealing with the greatly increased size of modern data sets. is the most successful collection of online citizen science projects which have enabled more than 800,000 online volunteers to contribute to over a dozen research projects. I will describe some of the science results to date from the Zooniverse collection of online projects, including the original Galaxy Zoo (Sloan Digital Sky Survey data) and (data from NASA's Kepler mission) with a focus on serendipitous discoveries made by participants. I will then discuss future developments of the Zooniverse platform in the context of new approaches to machine learning to assess volunteer behavior with the ultimate goal of producing a system that can balance classifications from humans and machines in real time. Such efforts are critical in coping with data from the next generation of large-scale experiments, including the LSST and SKA.

Date:   Wednesday 09-Oct-2013
Speaker:   Prof. Nitya Kallivayalil (University of Virginia)
Title:  The Magellanic Clouds and Stream: Galactic Accretion in Action

I present proper motions (tangential velocities) for the Large & Small Magellanic Clouds (LMC & SMC) based on three epochs of Hubble Space Telescope data, spanning a 7 year baseline, and centered on background quasars. The Magellanic Clouds are two of the largest and most prominent dwarf galaxies associated with the Milky Way. The high quality of the data has allowed us to measure their velocities to unprecedented precision, leading to some unexpected results. I will discuss the consequences of these new measurements for our understanding of the global dynamics of the Milky Way-LMC-SMC system. By mapping the variations in proper motion across the face of the LMC, it has been possible to measure its proper motion-rotation field and rotation curve, the first time this has been possible for any galaxy. This work is part of a larger effort towards 6-D mapping of the Milky Way and Local Group.

Date:   Wednesday 16-Oct-2013
Speaker:   Prof. Jenny Greene (Princeton University)
Title:  To Build an Elliptical Galaxy

I discuss two essential aspects of elliptical galaxy formation: how they get their stars, and how they lose their gas. For the former, I use integral-field observations of local massive galaxies to study the stellar populations and kinematics of stars at large radius, to understand the origin of the size growth of elliptical galaxies. Then I focus on black hole feedback as a means of clearing gas from massive galaxies. I show that luminous obscured quasars have ubiquitous, round ionized outflows with very high gas dispersions of nearly 1000 km/s out to 20 kpc. Finally, if time permits I will combine these two themes and present our recent search for sub-pc supermassive black hole binaries.

Date:   Wednesday 23-Oct-2013
Speaker:   Dr. Julie Hlavacek-Larrondo (Stanford University/University of Montreal)
Title:  "Rise of the titans, the biggest black holes in the Universe"

One of the most fascinating discoveries in modern astrophysics has been the realization that massive black holes can have a profound impact on their host galaxies. This impact appears mostly in the form of AGN feedback and during this talk, I will review the current status of this field while focusing on the most massive black holes in the Universe, those that lie at the centres of clusters of galaxies. I will address how AGN feedback evolves in such systems over the last 8 Gyrs, and discuss the implications of these results in terms of our understanding of black hole physics.

Date:   Wednesday 30-Oct-2013
Speaker:   Dr. Tom Statler (OHU/NSF)

The recoil due to the reflection and emission of photons from a Sun-irradiated surface is a major driver of dynamical evolution for small asteroids—especially the sorts that pose an impact hazard for Earth. The net recoil force (the Yarkovsky effect) drives evolution of the orbital elements; the net recoil torque (the YORP effect) drives evolution of the spin rate and axis orientation. Both effects are sensitively dependent on the spin state; hence understanding how spins evolve under the influence of YORP is crucial for understanding how orbits evolve under the influence of Yarkovsky. Previous work showed that monolithic, rigid asteroids should follow a largely deterministic “YORP cycle,” with long phases of rotational acceleration and deceleration. I will demonstrate, however, that YORP is so hypersensitive to the detailed topography of the surface that slight motions of loose material can qualitatively alter the torque and interrupt the cycle. The fact that most asteroids are probably not monolithic, but instead loosely-bound aggregates, has led to suggestions that continuous YORP acceleration may drive centrifugal mass shedding and the formation of binaries. However, we have performed the first self-consistent simulations of the YORP effect on dynamically evolving aggregates, and the results indicate that acceleration is rarely continuous. Instead, repeated reconfigurations of the body under the changing centrifugal force result in a random walk in spin rate and obliquity. This stochastic YORP evolution is qualitatively different from the YORP cycle, and, moreover, correctly predicts the distribution of orbits for asteroid families evolving under the Yarkovsky effect. These results have significant implications for binary formation and the feeding of asteroids onto Earth-crossing orbits, as well as for our understanding of the material properties of potential impactors.

Date:   Wednesday 06-Nov-2013
Speaker:   Dr. Jo Bovy (IAS)
Title:  New measurements of the Milky Way's mass distribution

The Milky Way’s (MW) density distribution in its inner parts and its decomposition into disk and halo components are fundamental to our understanding of the MW’s formation and evolution and to determining the importance of dark matter within the inner parts of galaxies. However, both the circular velocity curve and the density distribution away from the Galactic mid-plane are poorly constrained, especially away from the solar radius. I will present new dynamical measurements of the MW's rotation curve and surface density between 4 and 10 kpc. These allow us to separate the disk and halo contributions to the gravitational potential and to determine the radial profile of the dark matter halo.

Date:   Wednesday 13-Nov-2013
Speaker:   Dr. Arielle Moullet (NRAO)
Title:  Above the volcanoes: the mysterious atmosphere of Jupiter's moon Io

Io, Jupiter's innermost Galilean moon and the most volcanically active object in the Solar system, holds a tenuous and patchy atmosphere mainly composed of sulfur dioxide. This atmosphere continuously feeds the plasma torus in orbit around Jupiter, and thus requires the existence of very efficient replenishing mechanisms. While extensive observations from planetary missions, space telescopes and ground-based facilities have greatly contributed to its physical and chemical characterization, the respective roles of gas sources and the global structure of the atmosphere are still not well constrained. I will present the most significant advances achieved in the understanding of the nature of Io's atmosphere and the mechanisms shaping it, focusing on results obtained from (sub)millimeter wavelengths observations. This technique allows one to investigate the atmospheric composition, temperature, spatial distribution and dynamics. New observations obtained from the transformational ALMA interferometer (Atacama Large Millimeter Array) will also be presented.

Date:   Wednesday 20-Nov-2013
Speaker:   Prof. Hilke Schlichting (MIT)
Title:  'Planet Formation in the Kepler Era'

In my talk, I will discuss recent insights that we have gained into planet formation form the Kepler Satellite and our Solar System. I will give an overview of the planet formation process and show how it compares with recent observations of Exoplanet systems discovered by Kepler. I will present a simple model for orbital resonances with dissipation and show that it can explain the surprising paucity of mean motion resonance among exoplanet pairs and discuss its implications for the origin of these systems. I will conclude with dynamical models and geochemical constraints from the Earth, Moon and Mars and discuss their implications for the last stage of terrestrial planet formation.

Date:   Wednesday 27-Nov-2013

Date:   Wednesday 04-Dec-2013
Speaker:   Dr. Linda Elkins-Tanton (Carnegie DTM)
Title:  Building Earth-like planets: From gas and dust to ocean worlds

To begin to understand what makes a planet habitable, and thus where to look for life both within and outside of Earth’s solar system, we need to understand what in planetary formation and what in its subsequent evolution combine to produce a habitable planet. Though many things may help to make a habitable planet, only one thing is indispensible: liquid water. Geochemical observations indicate that the bulk of Earth’s water came from rocky planetesimals similar to asteroids. The accretionary impacts that add these materials to a growing planet during the first tens of millions of years of the solar system, culminating with the giant Moon-forming impact on Earth, had been thought to dry their target materials through heat and fragmentation. New mission data from Mars, the Moon, and Mercury, however, all indicate that these bodies have water in their interiors that originated with accretion, and so accretionary processes do not dry rocky planets. Models also indicate that sufficient water existed on the early Earth, even immediately after the Moon-forming impact, to form water oceans. Models further indicate that cooling and formation of an ocean occur very quickly, on the order of 10 millions years or less. Though this first wet atmosphere may be partially lost through erosion by an active young star, indications are that rocky planets accrete with water and may widely be expected to form early water oceans and thus open the potential for early habitability.

Date:   Wednesday 11-Dec-2013
Speaker:   Prof. Daniel Wang (University of Massachusetts)
Title:  "Everyday life of supermassive black holes: a long X-ray close-up of Sgr A*"

Most supermassive black holes (SMBHs) are accreting at very low levels and are difficult to distinguish from the galaxy centers where they reside. Our own Galaxy's SMBH, Sgr A*, provides an instructive exception. A close-up view of its x-ray emission based on recent 3 megaseconds of Chandra observations has provided new insights into the interplay of the SMBH with its environment. The x-ray emission from this central source is well resolved to have an elongated morphology, which aligns well with a surrounding disk of massive stars. We can rule out a concentration of low-mass coronally active stars as the origin of the emission on the basis of the lack of predicted Fe-Kalpha emission. The extremely weak H-like Fe-Kalpha line, relative to the strengths of transitions at lower ionization states, further suggests the presence of an outflow from the accretion flow onto the SMBH. This outflow likely removes more than 99\% of the material initially captured by the SMBH. We characterize the properties of hot plasma at the Bondi radius of the SMBH to explore the inflow and outflow interplay. These results provide important constraints for models of the prevalent radiatively inefficient accretion state.

This page was automatically generated on: 13-Jan-2016.