List of Past Astronomy Colloquia : 01-Jan-2014 to 01-Jun-2014

Date:   Wednesday 05-Feb-2014
Speaker:   Dr. Linda Strubbe (Canadian Institute for Theoretical Astrophysics)
Title:  "Studying Massive Black Holes Using the Tidal Disruption of Stars"

A star that wanders too close to a massive black hole gets shredded by the black hole's tidal gravity. Stellar gas soon falls back to the black hole at a rate initially exceeding the Eddington rate, releasing a flare of energy as gas accretes. How often this process occurs is uncertain at present, as is the physics of super-Eddington accretion (which is relevant for black hole growth and feedback at high redshift as well). Excitingly, in just the last couple of years, new transient surveys like Pan-STARRS, the Palomar Transient Factory, and surprisingly the Swift hard X-ray satellite are, for the first time, finding and following up tidal disruption event candidates in real time. I'll describe recent discoveries and what we're learning from them theoretically, in particular the event PS1-10jh (Gezari et al. 2012); I'll also look to the future at what measured rates of tidal disruption will be able to teach us about massive black holes and their surrounding galactic nuclei.

Date:   Wednesday 12-Feb-2014
Speaker:   Dr. Sarah Shandera (Penn State)
Title:  "Learning about primordial physics from large scale structure"

Early universe cosmology is entering a new phase thanks to more precise measurements constraining the primordial density inhomogeneities. Current and near future large scale structure surveys are pursuing statistics of the inhomogeneities beyond the well-measured power spectrum, and will eventually improve on the recent results from the Planck satellite. The potential of these new statistics has changed the way we think about theories of the primordial universe, including inflation. I will present the current understanding of how new data may illuminate the particle physics of inflation. I will also present new results, motivated by possible signatures of primordial physics in the halo bias, on an old issue in inflation: our ability to test the theory is limited by the fact that we observe a single, finite universe.

Date:   Wednesday 19-Feb-2014
Speaker:   Dr. Mark Krumholz (UC Santa Cruz)
Title:  The Origin of Stellar Masses

The mass distribution of newborn stars, known as the initial mass function (IMF), has a distinct peak at a mass slightly less than that of the Sun. This characteristic stellar mass appears to be nearly invariant across a huge range of star-forming environments, and over most of cosmic time. Explaining its origin and universality is one of the oldest problems in theoretical astrophysics, and a fully successful theory eludes us even today. In this talk, however, I describe recent progress toward an explanation for the mass scale of stars. This work is based on radiation-hydrodynamic simulations, which elucidate the way forming stars feed back on their environments and regulate the process of turbulent fragmentation that determines the IMF. Using insight from these simulations, I show that it may even be possible to express the characteristic mass of stars in terms of fundamental constants.

Date:   Wednesday 26-Feb-2014
Speaker:   Dr. Louis Strigari (Indiana University)
Title:  Micro and macro-physics in searches for dark matter.

I will discuss several recent instances in which understanding the large scale distribution of dark matter in dwarf galaxies and in the Milky Way has affected the interpretation of results from dark matter searches. In the case of Fermi-LAT, modeling of dwarf galaxies has set robust limits on the WIMP cross section, while for direct WIMP detection experiments understanding the highest velocity WIMPs in the halo strongly affects current upper limits (or possible signals). I will then discuss how modeling the distribution of dark matter in Local Group galaxies informs us about cold, warm, and self-interacting dark matter, and the physics of baryons on these scales.

Date:   Wednesday 05-Mar-2014
Speaker:   Dr. Evan Skillman (University of Minnesota)
Title:  The Local Cosmology from Isolated Dwarfs (LCID) Project

I will present an overview of the LCID project - a large Hubble Space Telescope program aimed at deriving detailed star formation and chemical enrichment histories for a sample of isolated Local Group dwarf galaxies. The details of the early star formation histories of isolated dwarf galaxies can shed light on the roles of the cosmic re-ionization and supernova feedback in galaxy formation and evolution. The radial gradients in the star formation histories provide insight into the structural evolution of dwarf galaxies. The variable star populations provide independent constraints on the strengths and distributions of the earliest star formation. Comparison of the star formation histories with various galaxy evolution models demonstrate that star formation is not directly coupled to mass assembly in dwarf galaxies. Comparing the results for isolated dwarfs with those obtained for the Milky Way and M31 satellites sheds new light on the effects of environmental mechanisms, which are expected to dominate for satellite galaxies.

Date:   Wednesday 12-Mar-2014
Speaker:   Dr. Warren Skidmore (Thirty Meter Telescope Observatory)
Title:  Thirty Meter Telescope: The Next Generation of Ground Based Optical/Infra Red Observatory

I will discuss some of the scientific capabilities that the Thirty Meter Telescope will provide and some of the areas of study that will benefit from the TMT's capabilities. I'll describe how the telescope design was developed to support a broad range of observing capabilities and how the observatory is being engineered. Finally I'll describe the avenues through which individuals can actively participate in the project and in planning for a potential TMT/NSF partnership.

Date:   Wednesday 26-Mar-2014
Speaker:   Dr. Elaine Oran (UMD)
Title:  How Do Type Ia Supernovae Explode? Studies of Turbulent Combustion

The development and evolution of turbulent burning fronts are critical components in all natural, deliberate, or accidentally produced high-speed combustion scenarios. This includes, for example, Type Ia thermonuclear supernovae (SNIa), engines for high-speed flight, and accidental catastrophes surrounding fuel storage plants (such as Buncefield, UK) and coal mines (such as Sago, WV). In the most general picture, the combustion process starts from a weak spark or small flame, evolves to a turbulent flame that subsequently grows in intensity and speed, and might undergo a transition to a detonation. In this presentation, we first show the physics of the combustion process through descriptions of experiments, accident investigations, and direct numerical simulations. Then we will focus on an underpinning physical question of how a flame interacts with a turbulent background field. Through the course of this discussion, we will indicate how general properties of flames and detonation can apply to SNIa explosions, and how we can use them to address the question of the origin of the transition to detonation in SNIa.

Date:   Wednesday 02-Apr-2014
Speaker:   Dr. Brice Menard (Johns Hopkins University)
Title:  The large-scale distribution of baryons

On scales larger than galactic disks the distribution of baryons in the Universe is still poorly understood. On those scales we happen to have a better mapping of the enigmatic dark matter distribution than those of gas and dust. Inspired by the statistical analyses used in weak lensing I will show how it is possible to reveal the distribution of baryons by measuring extremely low levels of absorption and extinction induced by the presence of metals. Using data from the Sloan Digital Sky Survey I will present new results showing how gas and dust are distributed well beyond galactic disks, up to Mpc scales. Finally, I will discuss how this new type of information can be used to better understand the physics of galaxy formation and evolution.

Date:   Wednesday 09-Apr-2014
Speaker:   Dr. Charles Bennett (Distinguished Alumnus of the Year - Johns Hopkins University)
Title:  Cosmology and the Cosmic Microwave Background

Studies of the Cosmic Microwave Background (CMB) have led to major advances in cosmology. In this talk I will summarize recent CMB results and their implications for cosmology. I will compare and contrast WMAP and Planck results and also discuss other select cosmological measurements that do not involve the CMB, both past and future. I will focus on how these measurements help to test cosmological models and narrow the range off their associated parameters. Specific topics will include constraints on the Hubble constant and on the parameters of inflation models.

Date:   Wednesday 16-Apr-2014
Speaker:   Dr. Karl Stapelfeldt (NASA/GSFC)
Title:  Scattered Light Imaging of Circumstellar Disks

Planetary systems are born in dense circumstellar disks and retain tenuous dust disks throughout the life of their central star. Scattered light imaging has provided the highest resolution views to date of disk structures; in combination with thermal infrared measurements, modeling can be used to constrain the size and scattering properties of their constituent dust. We have used far-IR survey data from the Spitzer Space Telescope to select the best disk targets for imaging with the Hubble Space Telescope. Our HST images reveal eleven new examples of edge-on protoplanetary disks. Outstanding individual sources show evidence for dust grain evolution and an asymmetric disk with misaligned jet which likely traces tidal perturbations in a binary system. Our debris disk survey detected a new eccentric ring suggestive of a distant outer planet to a nearby solar-type star, but most other debris disks remain undetected at the contrast levels accessible to HST. New developments in groundbased adaptive optics, and especially future space telescopes with a new generation of coronagraphs, will be key to advancing the study of disk scattered light in the ALMA era.

Date:   Wednesday 23-Apr-2014
Title:  PSC Dedication

Date:   Wednesday 30-Apr-2014
Speaker:   Dr. Shrinivas Kulkarni (Caltech)
Title:  "Booms, Burps & Bumps: The Dynamic Universe"

That occasionally new sources ("Stella Nova") would pop up in the heavens was noted more than a thousand years ago. The earnest study of cosmic explosions began in earnest less than a hundred years ago. Over time astronomers have come to appreciate the central role of supernovae in synthesizing new elements (and making life as we know possible).

The Palomar Transient Factory (PTF), an innovative 2-telescope system, was designed to explicitly chart the transient sky with a particular focus on events which lie in the nova-supernova gap. PTF can find an extragalactic transient every 20 minutes and a Galactic (strong) variable every 10 minutes. The results so far: classification of 2000 supernovae, identification of an emerging class of ultra-luminous supernovae, the earliest discovery of a Ia supernovae, discovery of luminous red novae, the most comprehensive UV spectroscopy of Ia supernovae, discovery low energy budget supernovae, clarification of sub-classes of core collapse and thermo-nuclear explosions, mapping of the systematics of core collapse supernovae, identification of a trove of eclipsing binaries and the curious AM CVns.

Date:   Wednesday 07-May-2014
Speaker:   Dr. Jennifer Lotz (STscI)
Title:  The Frontier Fields and Beyond

How deep can we go? What are the faintest and most distant galaxies we can see with the Hubble Space Telescope now, before the launch of the James Webb Space Telescope? This is the challenge taken up by the Frontier Fields, a new director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields will combine the power of HST with the natural gravitational telescopes of high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. These observations will reveal distant galaxy populations ~10-100 times fainter than any previously observed, allowing astronomers to study the early progenitors of the Milky Way and the faint galaxies responsible for reionization. I will review the prospects for studying galaxies at cosmic dawn with JWST, extremely large ground-based telescopes such as the Thirty Meter Telescope and Giant Magellan Telescope,and future space missions over the next decade and beyond.

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