Astrophysics Science Division Colloquium Series
Schedule: Spring 2015

Astrophysics Science Division Colloquium Series
Schedule: Spring 2015

Recent schedules:

2014, Fall 2014, Spring  
2013, Fall 2013, Spring 2013, Summer
2012, Fall 2012, Spring  
2011, Fall 2011, Spring  
2010, Fall 2010, Spring  

ASD Colloquia are Tuesdays at 3:45 pm (Meet the Speaker at 3:30 pm)
in Bldg 34, Room W150 unless otherwise noted.


Jan 6 AAS Meeting
Jan 13 660 Town Hall
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) - Recent Results on the Galactic Black Hole and its Entourage
Mar 31 Yoram Lithwick (Northwestern) - Extrasolar Planets: Lessons From Kepler


Apr 7 Michelle Larson (Adler) - Science Has a Story to Tell
Apr 14 Ed Bertschinger (MIT) - How Culture Helps or Hinders You and Your Colleagues
Apr 21 John Cannizzo (GSFC) - Clues to the evolution of helium WD-WD binaries from the PTF
Apr 28  


May 5 Mike Boylan-Kolchin (UMD) - The Local Universe as a Cosmological Laboratory
May 12 Jennifer Donovan Meyer (NRAO) - Dwarf Galaxies on the Edge of the Local Volume
May 19 Tony Del Genio, Shawn Domagal-Goldman, & Jeremy Schnittman (GSFC)
From Earth Climates to Exoplanet Atmospheres, and Back Again
May 26 NO COLLOQ (Memorial day)
Jun 2 Ann Hornschemeier (GSFC) - X-ray Binary Populations from 0.5-30 keV with NuSTAR and Chandra

There’s Government in Your Science

Josh Shiode

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

Jillian Bellovary


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

Vladimir Airapetian


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

Sarah Gallagher


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

Damiano Caprioli


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.

Dynamics of Mass Transfer and Accretion in X-Ray Binaries

John Blondin

North Carolina State University

Tuesday, Mar 17, 2015


Our x-ray sky is lit up by numerous x-ray binaries, including the first cosmic x-ray source discovered in 1962, Sco X-1. The bright flux of x-rays is fueled by gas from a close companion star that is accreted onto a black hole or neutron star. As the gas falls into the deep gravitational potential well of the compact star, it is heated to millions of degrees and emits x-rays. This concept of mass transfer is seen in numerous artist illustrations, but how in fact does the gas get from the donor star to the compact companion? I will show several examples where large-scale three-dimensional simulations can now be used to study specific features of mass transfer, from the variability due to accretion of gas from a clumpy wind or the cyclic feedback of x-ray heating to the structure and evolution of a tilted accretion disk.

Recent Results on the Galactic Black Hole and its Entourage

Mark Morris


Tuesday, Mar 24, 2015


Sagittarius A*, the name given to nonthermal infrared and radio emission from the immediate surroundings of the Galactic Black Hole - is continously variable. Recent monitoring with adaptive optics on large telescopes, and with the Spitzer telescope is refining our characterization of the statistical characteristics of this red noise process, but so far offering few hints to the geometry of the emission mechanism, other than that it has been stable for over a decade, and shows no evidence for orbital modulation. I’ll describe the present situation, and will also discuss what has been learned from observations of X-ray flares from Sgr A*. There has been much excitement about the possibility that the accretion rate onto Sgr A* will soon increase as a result of the passage of a mysterious, compact, dusty object, G2, through its close orbital periapse. Existing observations, including those of our UCLA Galactic Center Group with the Keck Telescopes, show that G2 has both extended and compact components, and we have proposed that it is stellar in nature rather than the originally proposed cloud of gas and dust. New insights are being provided by a similar object, G1, which passed near Sgr A* about 15 years ago on a similar orbit. Finally, I’ll provide an update on what we are learning from our 20 years of monitoring of stellar orbits around the black hole, and how we expect to be able to undertake new tests of General Relativity in coming years. Time permitting, I’ll also discuss the X-ray and radio evidence that Sgr A* has a jet.

Extrasolar Planets: Lessons From Kepler

Yoram Lithwick


Tuesday, Mar 31, 2015


Astronomers have been discovering extrasolar planets at an astonishing pace. In the past few years alone, the Kepler space telescope has discovered thousands of planets smaller than Neptune. Many of these planets' properties were completely unexpected, based on how planets were thought to form. I will describe these surprising properties, and explain how we have inferred the densities and eccentricities of dozens of exoplanets from their "transit time variations." These and other discoveries point to new elements that are needed in the paradigm of planet formation.

Science Has a Story to Tell

Michelle Larson


Tuesday, Apr 7, 2015


In 2002 I had the pleasure of hearing Alan Alda deliver the commencement address at Caltech. In his remarks he presented a call to action, "I'm asking you today to devote some significant part of your life to figuring out how to share your love of science with the rest of us......Whatever you do, help us love science the way you do........What if each of you decided to take just one thing you love about science and, no matter how complicated it is, figure out how to make it understood by a million people?........How you do it is up to you. You’re clever people, and I bet you come up with some ingenious solutions."

The public is inspired and intrigued by the frontiers of research science, and the methods by which we reach broader audiences can take many forms. In this talk I will discuss a variety of approaches for showcasing research outside the borders of individual departments, and we'll explore specific examples of how to unwrap frontier science, and invite others into the process and journey that is scientific discovery.

How Culture Helps or Hinders You and Your Colleagues

Edmund Bertschinger


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.

Clues to the evolution of helium WD-WD binaries from the PTF

John Cannizzo


Tuesday, Apr 21, 2015


The study of AM CVn stars - semi-detached He WD-WD binaries - has exploded in recent years thanks to long term light curves obtained by the Palomar Transient Factory. Systems are seen with binary periods ranging from about 5 minutes to about an hour. AM CVn stars are similar to dwarf novae in that they can undergo accretion disk outbursts. Systems with high dM/dt have steady disks in permanent outburst, whereas for very low dM/dt systems the disks are too cool to have outbursts. Disk instability theory gives a specific prediction for the zone of instability, therefore by matching the observed zone with the theoretical one we constrain dM/dt(P_orb), the rate of mass transfer versus orbital period. The inferred relation is consistent with expectations from stellar evolution. One also has predictions for the recurrence time for outbursts and outburst duration versus P_orb which can be compared to observations.

The Local Universe as a Cosmological Laboratory

Michael Boylan-Kolchin


Tuesday, May 5, 2015


The Local Group affords us the opportunity to study the low-mass extremes of galaxy formation and cosmology. In this capacity, it presents some of the most enduring challenges to the very successful LCDM cosmology. I will discuss to what degree standard theoretical models of the local Universe match the growing volume and diversity of observations in the Local Group and beyond, with an emphasis on what these data may reveal about the nature of dark matter and the low-mass threshold of galaxy formation. Since cosmic reionization is expected to be an important process in determining the abundance of low-mass galaxies around the Milky Way, a promising way to learn about the high-redshift Universe is to study its descendants locally. I will argue that, even in the JWST era, the local Universe may be our best probe of low-mass galaxies at high redshift that are expected to be crucial for reionization.

Dwarf Galaxies on the Edge of the Local Volume

Jennifer Donovan Meyer


Tuesday, May 12, 2015


I will discuss ongoing work in which we address the mass assembly of galaxies at late times by exploiting observations of their occasionally faintly star-forming neutral hydrogen content. Specifically, I will describe the search for, and confirmation of, tiny dwarf galaxies in the vicinity of the Local Group. We start with two recent "all-Arecibo sky" surveys and search for dwarfs via their HI signatures. Dwarf galaxies probe not only one of the more easily recognizable methods of ongoing accretion of gas and stars onto galaxies, but they also represent some of the lowest rates (and in many cases the most metal poor examples of) recent star formation. Dwarfs in the vicinity of the Milky Way provide the added advantage of being nearby enough to study at relatively high resolution, which is especially useful in the context of being potential nearby analogs to high redshift, low mass star forming galaxies. The sample I present thus yields insight into the ongoing baryonic mass assembly of the Milky Way; it also can be used to investigate, with high resolution, star formation in galaxies dominated by pristine atomic gas.

From Earth Climates to Exoplanet Atmospheres, and Back Again

Tony Del Genio, Shawn Domagal-Goldman, & Jeremy Schnittman


Tuesday, May 19, 2015


In this tag-team talk we will describe some of the recent work done at GISS and here in Greenbelt by our Strategic Task Group (STG) on comparative climatology. We will present a brief history of the effort, beginning with a Science Innovation Fund (SIF) proposal in 2012, leading up to the recent announcement of "NASA's NExSS coalition to lead search for life on distant worlds," and looking forward to the future of analyzing real observations with future telescopes like JWST and ATLAST. The central thread of this large, interdisciplinary effort has been the application of tools originally developed for Earth science to other Solar System and Extrasolar planets. Along the way, the testing and development of global circulation models (GCMs) has in turn expanded their range of applicability here on Earth, and in more than a few places improved their reliability.

X-ray Binary Populations from 0.5-30 keV with NuSTAR and Chandra

Ann Hornschemeier


Tuesday, June 2, 2015


The X-ray emitting properties of accreting black hole (BH) and neutron star (NS) binary populations, collectively referred to as X-ray Binaries (XRB)s, appear to correlate well with galaxy parameters such as star formation rate (SFR) and stellar mass. These correlations have been well-studied in both the local universe and to higher redshift using the Chandra X-ray Observatory which has permitted spatially resolved studies in the 0.5-10 keV band. However, with the 0.5-10 keV band alone, there are ambiguities concerning the identity and states of the sources. Recently, we have extended work on extragalactic XRB populations to E>10 keV using the unprecedented imaging capability of the NuSTAR Explorer mission to study a sample of ~6 galaxies in the relatively nearby universe. We've built upon intensity-count rate diagnostics for Milky Way XRBs, determined from a rich database of RXTE PCA spectra, to enable direct constraint on the source identities and accretion states of binaries. In this talk, results on these nearby galaxies are covered, as well as some of the implications for X-ray emission from XRB populations in the earlier Universe. Among these is that X-ray emission from star-forming galaxies may play an appreciable role in the early heating of the Intergalactic Medium and may also have a significant role in reionization.

Jeremy Schnittman
NASA Logo, National Aeronautics and Space Administration