|2014, Fall||2014, Spring|
|2013, Fall||2013, Spring||2013, Summer|
|2012, Fall||2012, Spring|
|2011, Fall||2011, Spring|
|2010, Fall||2010, Spring|
|Jan 6||AAS Meeting|
|Jan 13||660 Town Hall|
|Jan 20||NO COLLOQ (MLK)|
|Jan 27||Josh Shiode (AAS) - There’s Government in Your Science|
|Feb 3||Jillian Bellovary (Vanderbilt) - Scrutinizing the Relationship Between Galaxies and Supermassive Black Holes|
|Feb 17||NO COLLOQ (President's Day)|
|Feb 24||Vladimir Airapetian (GSFC) - The Hadean Earth Under a Coronal Mass Ejection Attack: Prospects For Life|
|Mar 3||Sarah Gallagher (UWO) - Winds, Winds Every Where: Radiatively Driven Outflows from Supermassive Black Holes|
|Mar 10||Damiano Caprioli (Princeton) - New Insights into Particle Acceleration at Shocks|
|Mar 17||John Blondin (NCSU) - Dynamics of Mass Transfer and Accretion in X-ray Binaries|
|Mar 24||Mark Morris (UCLA)|
|Mar 31||Yoram Lithwick (Northwestern)|
|Apr 7||Michelle Larson (Adler)|
|Apr 14||Ed Bertschinger (MIT) - How Culture Helps or Hinders You and Your Colleagues|
|May 5||Mike Boylan-Kolchin (UMD)|
|May 12||Jennifer Meyer (NRAO)|
|May 26||NO COLLOQ (Memorial day)|
There’s Government in Your Science
John N. Bahcall Public Policy Fellow, American Astronomical Society
Tuesday, Jan 27, 2015
The majority of basic science research in the United States — including that in the astronomical sciences — is funded by the federal government. This is both good and bad. Good because there are a lot of resources available, though basic research funding is but a small fraction of the total federal budget. Bad because individual scientific projects, and the careers of the scientists involved, can be affected by political winds they would otherwise never feel. In this talk, I’ll try to convey a sense of those winds. I’ll focus on the process of policymaking and long-term trends relevant to the scientific enterprise, and we’ll explore how individual scientists and science advocates can play a role in the political and policymaking process.
Scrutinizing the Relationship Between Galaxies and Supermassive Black Holes
Tuesday, Feb 3, 2015
Supermassive black holes (SMBHs) have a ubiquitous presence in massive galaxies, but their formation and evolutionary history remain mysteries. One of the strongest observed trends between SMBHs and their host galaxies is the tight relation between black hole mass and the velocity dispersion of the stellar spheroid (aka the M-Sigma relation). While this relation hints at a fundamental link between galaxy and SMBH growth, there are also some challenges regarding scatter and outliers. I will present evidence that the M-Sigma relation is not the clear-cut trend it seems to be; for example, the orientation of galaxies on the sky affects the value of velocity dispersion by up to 30%. Additionally, the existence of SMBHs in dwarf galaxies and galaxies without spheroids challenges the standard paradigm of SMBH-galaxy coevolution. I will offer some alternative methods of forming and growing SMBHs which can provide explanations for these puzzling outliers.
The Hadean Earth Under a Coronal Mass Ejection Attack: Prospects For Life
Tuesday, Feb 24, 2015
At a time when the number of exoplanets observed is skyrocketing, the field of astrobiology is still searching for a better understanding of whether or when life may have begun on those planets – or how long they could remain viable for life. Recent Kepler observations suggest that active G-type stars are capable of producing extremely powerful flares called superflares, with energies up to 10,000 times greater than that observed on the Sun. These stars resemble our ´infant" (0.5 Myr) Sun. Thus, the Hadean Earth may also have been exposed to such solar superflares from the young Sun. We show that super-CME (SCME) events with the energy of 3-10 times the energy of the Carrington event were hitting the Earth’s magnetosphere with a frequency of ~1 event per day!
What was the impact of superflares and associated coronal mass ejections (CMEs) and Solar Proton Events (SEPs) on the atmospheric erosion of the young Earth and planetary habitability? How did the Earth environment respond to such impacts? Did superCMEs help to form pre-biotic chemistry or inhibit the development of surface life on the Hadean Earth? What would be the expected consequences of a superCME on the current Earth environment?
The results of our 3D MHD simulations suggest that frequent and energetic SCMEs from the early Sun continuously destroyed the sub-solar parts of early Earth's magnetosphere at heights less than 1 Earth's radius. This critical finding suggests that CME shock accelerated energetic protons are capable of breaking atmospheric molecular nitrogen, the major ingredient of the early Earth’s atmosphere, into atomic nitrogen. This is a major process that produces hydrogen cyanide, which is an essential molecule in prebiotic life chemistry including the RNA molecule, a precursor of life. This raises an intriguing possibility that frequent super-CMEs could be a potential catalyst of first life forms on early Earth and Mars. Our scenario provides a potential answer to the “faint young Sun” paradox suggesting that the direct heating comes from the energy dissipated in collisions of protons with the Earth’s atmosphere. Our model is also consistent with high values of isotopic ratios of 14N/15N observed in the solar wind and the Earth’s atmosphere.
Winds, Winds Every Where: Radiatively Driven Outflows from Supermassive Black Holes
Tuesday, Mar 3, 2015
Supermassive black holes reside in the centers of every massive galaxy. In relatively brief spurts, black holes grow as luminous quasars through the infall of material through an accretion disk. Remarkably, the light from the accretion disk can outshine all of the stars in the host galaxy by a factor of a thousand, and this radiation can also drive energetic mass outflows. Mass ejection in the form of winds or jets appears to be as fundamental to quasar activity as accretion, and can be directly observed in many objects with broadened and blue-shifted UV emission and absorption features. A convincing argument for radiation pressure driving this ionized outflow can be made within the dust sublimation radius. Beyond, radiation pressure is still important, but high energy photons from the central engine can now push on dust grains. This physics underlies the dusty wind picture for the putative obscuring torus. I'll describe our model of the dusty wind and evaluate its successes and shortcomings in accounting for observed properties of quasars such their mid-infrared spectral energy distributions, fractions of hidden objects, and column densities of important ions.
New Insights into Particle Acceleration at Shocks
Tuesday, Mar 10, 2015
Particle-in-cell simulations are providing us unprecedented insights into the microphysics of collisionless shocks, also probing their abilty to accelerate particles and generate magnetic fields. I present state-of-the-art kinetic simulations of non-relativistic shocks, discussing under which conditions (shock strength and inclination) ions and electrons are injected and energized via diffusive shock acceleration. I also outline how the initial magnetic field is amplified by different plasma instabilities induced by energetic particles, which has both observational and theoretical implications. Finally, I discuss the relevance of these findings for particle acceleration in interplanetary shocks, and in astrophysical sources such as supernova remnants and galaxy clusters.
How Culture Helps or Hinders You and Your Colleagues
Tuesday, Apr 14, 2015
Culture is the dark energy of our lives: it is an invisible force that shapes our environment for work and life. Culture shapes climate, and climate affects individual and group satisfaction and accomplishment. A culture of exclusion is one that fails to recognize and correct for unconscious bias, marginalization of out-group members, privilege, etc. A culture of inclusion advances a respectful and caring community to leverage the power of diversity, improve employee success, and enhance the quality of life for everyone. I will describe a study of community and culture at MIT, and steps we have taken and are taking to create a culture of empowerment and respect for everyone.