MIT Astrophysics Colloquia - Spring 2015

Tuesdays at 4:00 PM in the Marlar Lounge, Room 37-252
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar Street, Cambridge, MA
(unless location otherwise noted)
Refreshments are served at 3:45 PM.

Sponsored by
the Astrophysics Division of the MIT Department of Physics and
the MIT Kavli Institute for Astrophysics and Space Research.

Tuesday Mar 3:
The Space Photometry Revolution of Asteroseismology & Exoplanets
Daniel Huber
University of Sydney
Host: Joshua Winn

Abstract: Asteroseismology - the study of stellar oscillations - is a powerful tool to probe the structure and evolution of stars. In addition to the wealth of newly discovered exoplanets, space-based telescopes such as Kepler have revolutionized asteroseismology by detecting oscillations in thousands of stars from the main sequence to the red-giant branch. In this talk I will highlight the most recent asteroseismic discoveries by Kepler/K2 with a particular focus on exoplanet host stars, and discuss efforts to improve stellar properties of the Kepler parent sample to derive accurate planet occurrence rates. I will also discuss the prospects for asteroseismic studies with TESS, including its role for the synergy of asteroseismology and galactic astronomy to probe the chemo-dynamical evolution of stellar populations in our Galaxy (galactic archeology).

Tuesday Mar 10:
Cosmic Neutrinos and Large-scale Structure
Marilena Loverde
Kavli Institute for Cosmological Astrophysics, University of Chicago
Host: Lia Corrales

Abstract: Cosmic background neutrinos are nearly as abundant as cosmic microwave background photons, but their mass, which determines the strength of their gravitational clustering, is unknown. Neutrino oscillation data gives a strict lower limit on neutrino mass, while cosmological datasets provide the most stringent upper limit. Even if the neutrino masses are the minimum required by oscillation data, their gravitational effects on structure formation will nevertheless be detectable in — and in fact required to explain — data within the next decade. I will discuss the physical effects of the cosmic neutrino background on structure formation and present a new signature that may be used to measure neutrino mass with large galaxy surveys.

Tuesday Mar 17:
Fast Radio Bursts - What Can We Say About Emission Mechanisms and Origins?
Jonathan Katz
Washington University in St. Louis
Host: Saul Rappaport

Abstract: The pulse widths, dispersion measures and dispersion indices of Fast Radio Bursts (FRB) impose coupled constraints that all models must satisfy. Conventional single thin screen scattering models imply electron densities were >~20/cm^3, 10^8 times the mean intergalactic density. This problem is resolved if the radiation scattered close to its source, where high densities are plausible. Observation of dispersion indices close to their low density limit of -2 sets a model-independent upper bound on the electron density and a lower bound on the size of the dispersive plasma cloud, excluding terrestrial or Solar System origin. The scattering and much of the dispersion may be attributed to regions about 1 AU from the sources, with electron densities ~ 3E8/cm^3. The inferred parameters are only marginally consistent; re-examination of the assumed relation between dispersion measure and distance is warranted. Origin in an ionized starburst or protogalaxy is suggested, but statistical arguments exclude cosmologically local compact young SNR.

Tuesday Mar 24:

Tuesday Mar 31:
Tracking Planet Footprints in Dusty Disks
Catherine Espaillat
Boston University
Host: Zach Berta-Thompson

Abstract: We know that most stars, if not all, were once surrounded by protoplanetary disks. How these young disks evolve into planetary systems is a fundamental question in astronomy. Observations of T Tauri stars (TTS) may provide insights into this question, particularly a subset of TTS with “transitional disks.” The spectral energy distributions of these objects feature an infrared "dip," indicating that they have developed holes or gaps in their dust disk. For many transitional disks, the inward truncation of the outer dust disk has been confirmed, predominantly through (sub)millimeter interferometric imaging. Many researchers have posited that these holes and gaps are the “footprints” of planets given that theoretical simulations predict that a young, forming planet will clear the material around itself, leaving behind a cavity in the disk. In this talk, I will review the key observational constraints on the dust and gas properties of transitional disks and examine these in the context of theoretical planet-induced disk clearing models. I will also discuss possibilities for future work in this field, especially in the context of the upcoming ALMA era.

Tuesday Apr 7:
New Insights into the Interstellar Medium in our Neighbor M31
Karin Sandstrom
Host: Lia Corrales

Abstract: As the nearest metal-rich, star-forming galaxy to the Milky Way, M31 plays a key role in understanding the interstellar medium (ISM) and star formation at z~0. Because of its proximity, we can study the properties of the ISM on the scale of individual star-forming molecular clouds and characterize the stellar sources of energy input for the ISM gas and dust. Recent observations have emphasized the importance cloud-scale processes in setting the efficiency of star formation. In particular, the formation of bound molecular clouds out of the cold neutral medium is a critical step in the process. Small spatial scale processes are also crucial for generating the tracers of star formation we use to study distant galaxies. M31 is currently the only metal-rich galaxy where existing observational facilities let us probe these important scales in all of the relevant tracers. Towards that end, we have assembled a powerful multi-wavelength observational dataset for a large portion of the disk of M31 - including HI 21-cm and radio continuum mapping from the VLA, CO J=(1-0) mapping from CARMA, Spitzer and Herschel photometry, Herschel spectroscopy, optical integral field spectroscopy, and resolved stellar photometry from the Pan-chromatic Hubble Andromeda Treasury (PHAT). I will summarize what we have learned about the connection between star formation and the ISM from this unique dataset.

Tuesday Apr 14:
Cosmology After Planck
David Spergel
Host: Max Tegmark

Abstract: The Planck Telescope has made an accurate full-sky measurement of the cosmic microwave background (CMB) temperature, the leftover heat from the Big Bang. These measurements probe both the physics of the very early universe and the basic properties of the universe today. The Planck measurements confirm the earlier results from the WMAP telescope and rigorously test our standard cosmological model and provide an accurate determination of basic cosmological parameters (the shape of the universe, its age, and its composition). When combined with other astronomical measurements, the measurements constrain the properties of the dark energy and the nature of dark matter. The observations also directly probe the physics of first moments of the Big Bang: the current data are consistent with the idea that the early universe underwent a period of rapid expansion called inflation. I will review the Planck data and preview the upcoming data from ground-based polarization experiments. I will also look forward to future measurements from LSST and WFIRST, the major ground and space-based surveys of the coming decade. Many key cosmological questions remain unanswered: What happened during the first moments of the big bang? What is the dark energy? What are the properties of the dark matter? The upcoming combination of large-scale structure, supernova and CMB measurements may provide new insights into these key cosmological questions.

Tuesday Apr 21:

Tuesday Apr 28:
Dark Matter Dynamics
Tom Abel
Kavli Institute for Particle Astrophysics and Cosmology, Stanford University
Host: Rob Simcoe

Abstract: Computational Physics allows us to study extremely non-linear systems with fidelity. In astrophysical hydrodynamics and studies of galaxy formation much of the last two decades we have explored various discretization techniques and found subtle differences in some applications. Interestingly numerical studies of collisionless fluids such as e.g. the collapse of cold dark matter to form the large scale structure of the Universe has only been studied meaningfully with one approach; N-body Monte Carlo techniques. I will introduce a novel simulation approach, and demonstrate its feasibility, that can study a collisionless system in the continuum limit in multi-dimensions. I will also show this new technique opens a new window in making sense of structure formation as well as plasma physics. In this context we have developed a novel rasterization/voxelization algorithm applicable in computational geometry, computational physics, CAD design and other fields. I show how these approaches allow also for much improved predictions for gravitational lensing, dark matter annihilation, properties of cosmic velocity fields, and a range of other interesting topics.

Tuesday May 5:
Lisa Kaltenegger
Host: Zach Berta-Thompson


Tuesday May 12:
Inflationary Relics in Cosmic Structures
Marc Kamionkowski
Johns Hopkins University
Host: Nevin Weinberg

Abstract: Inflation is a relatively simple idea that accounts remarkably well for a number of the features of the observed Universe. These features appear as very subtle patterns in the primordial mass distribution. I will explain how measurements have been used to verify a number of inflation's predictions. I will then describe an assortment of other subtle patterns predicted by various models for inflation that can be sought with future galaxy surveys and cosmic microwave background measurements.

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