MIT Astrophysics Colloquia - Fall 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 Sep 15:
Massive Elliptical Galaxies and Supermassive Black Holes
Chung-Pei Ma
UC Berkeley
Host: Rob Simcoe

Abstract: Massive elliptical galaxies exhibit the most massive black holes, most extreme stellar initial mass functions, and most dramatic size evolution over cosmic time. Yet, their complex formation histories remain obscure. I will describe the ongoing MASSIVE Survey, a volume-limited, multi-wavelength, spectroscopic and photometric survey of the structure and dynamics of the 100 most massive early-type galaxies within 100 Mpc. A combination of integral-field spectroscopy on sub-arcsecond and large scales allows us to perform simultaneous dynamical modeling of the supermassive black holes, stars, and dark matter. I will present first results from the survey and discuss the implications of black hole binaries as sources of gravitational waves for pulsar timing array experiments.

Tuesday Sep 22:
The Energy Balance of Short-Period Planets
Nicolas Cowan
McGill University
Host: TBD

Abstract: What started as a trickle in the mid 1990’s is now a torrent, with over one thousand extrasolar planets currently known, and thousands of candidates awaiting confirmation. The study of exoplanets has already revolutionized our view of planet formation, and will soon do the same to our understanding of planetary atmospheres and interiors. Since we view them from the top-down, one of the first aspects of exoplanet atmospheres to be constrained is their global thermal emission. By combining infrared emission measurements at a variety of orbital phases, we can infer a planet's Bond albedo, the efficiency of its day-night heat transport, and, in the case of planets subject to seasons, its thermal inertia. Multi-wavelength emission measurements can also constrain a planetary atmosphere's composition and vertical temperature structure. Such inferences are particularly sensitive to the uncertainty in emission measurements, however, and the accuracy of eclipse measurements has typically been over-stated. Fortunately, improved analysis techniques and next-generation instruments should allow us to resolve outstanding questions about hot Jupiters, and to extend our methods to temperate terrestrial planets.

Tuesday Sep 29:
What X-rays tell us about exoplanet systems
Katja Poppenhaeger
Queen's University Belfast
Host: Zach Berta-Thompson

Abstract: With thousands of exoplanetary systems known to date, characterizing the atmospheres of exoplanets and how they evolve over time has become an intensely studied question. While optical and near-infrared observations probe lower layers of exoplanetary atmospheres, high-energy observations reveal what happens to the upper atmospheric layers that interact with the stellar wind. Also, high-energy photons directly trace the magnetic activity of the host stars, and can be used to draw inferences about the stellar corona, stellar flares, and the rotational history of stars. I will discuss what this exciting observational window has told us so far about exoplanets and their host stars, and will also highlight some upcoming high-energy missions and how their capabilities can be used for the exoplanetary field.

Tuesday Oct 6:
From the Heliosphere, to Galaxy Clusters, Gamma Ray Bubbles, Pulsars and Black Holes: Unexpected Plasmas, Relevant and Laboratory Based Theories
Bruno Coppi
Host: TBD

Abstract: The in situ exploration of the Heliosphere has revealed the existence of unexpected kinds of plasmas and magnetic field configurations around the most distant planets (e.g. Uranus and Neptune) for which reliable theories can be formulated and be of help to envision the environments of a variety of recently discovered exo-planets. On larger scales, radically different kinds of plasmas have been found: in particular plasmas with “temperatures in the tens of keV are observed to be the main visible component of Galaxy Clusters, while g-ray emitting plasma structures (“bubbles”) have been seen to emerge from the disk of Our Galaxy with dimensions of the same order as those characterizing the Galaxy. Although the theory of the plasmas that can surround pulsars has a long history, the fact that the plasmas on the surface of pulsars can have inhomogeneous features (such as hot spots) and dynamics has gained attention recently. Given the very high magnetic fields involved, the role of the electron thermal conductivity anisotropy is shown to be an important factor in these. There are important issues to be resolved in order to envision the plasmas that can surround black holes. These involve the structures that can form, such as rings and tridimensional spirals, the kind of transport of angular momentum that is needed to allow plasma accretion on the black hole, etc. In fact, laboratory experiments on high-energy plasmas have cast new light on basic processes that include the nature of angular momentum transport not described by a diffusion equation, magnetic reconnection events and associated production of high-energy particles, self-organization processes, etc.

Tuesday Oct 13:
Implausible Life: An Unappealing But Plausible Scenario for Life's Origin on Earth
Ed Turner
Host: Joshua Winn

Abstract: There is no evidence which strongly contradicts the hypothesis that life arose on Earth due to such extraordinarily improbable events that it is extremely unlikely it has arisen or will ever arise elsewhere within the observable universe. Moreover, a few bits of evidence and lines of reasoning support this hypothesis, though none in a conclusive or compelling way. The ways in which molecular biology suggests combinatoric improbability, the Fermi(-Hart) paradox, "rare Earth" lines of argument and the failure to date of SETI are among them. Moreover, some of the most common counterarguments to these inferences are flawed in fundamental ways. However unappealing it may be (to most, but not all), we should take the hypothesis quite seriously at our current state of knowledge. It is arguably as good as any other available scenario on a purely empirical basis.

Tuesday Oct 20:
Atmospheric dynamics of brown dwarfs
Adam Showman
University of Arizona
Host: Michael McDonald


Tuesday Oct 27:
The Search for Alternate Universes
Ranga-Ram Chary
Host: Jacqueline Hewitt

Abstract: In the last few years, we have made remarkable progress in understanding the properties of our observable Universe which appears to have evolved from a hot Big Bang 13.7 billion years ago. The fine-tuning of initial conditions required to reproduce our present day Universe suggests that our Universe may merely be a region within an eternally inflating super-region. Many other regions could exist beyond our observable Universe with each such region governed by a different set of physical parameters than the ones we have measured for our Universe. Collision between these regions, if they occur, should leave signatures of anisotropy in the cosmic microwave background. I present spatial and spectral analysis of the cosmic microwave background data from Planck. I will focus on constraining properties at the epoch of recombination 270,000 years after the Big Bang and present the observational evidence in favor of alternate Universes.

Tuesday Nov 3:
The Heart of the Beast : The Relativistic Astrophysics of Active Galactic Nuclei
Chris Reynolds
University of Maryland
Host: Mark Bautz


Tuesday Nov 10:
Exploring the Diversity of Planetary Composition and Structure Through Exoplanet Transit Spectroscopy
Avi Mandell
NASA Goddard Center for Astrobiology
Host: Hans Moritz Guenther


Tuesday Nov 17:
Stochastic nuclear activity at the Galactic Centre
Joss Bland-Hawthorn
University of Sydney
Host: Anna Frebel


Tuesday Nov 24:
Dark Matter Signal or Backgrounds: How Can We Tell?
Tracy Slatyer
Host: Scott Hughes


Tuesday Dec 1:
Gravitational Wave Astronomy with Advanced LIGO
Chad Hanna
Pennsylvania State University
Host: Nergis Mavalvala


Tuesday Dec 8:
Mariska Kriek
UC Berkeley
Host: Paul Schechter


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