Astrophysics Science Division Colloquium Series
Schedule: Spring 2016

Astrophysics Science Division Colloquium Series
Schedule: Spring 2016

Recent schedules:

  2016, Spring  
2015, Fall 2015, Spring  
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 5 No Colloqium (AAS Meeting)
Jan 12 Francesco Tombesi (UMD) - How Can Supermassive Black Holes Drive the Evolution of Entire Galaxies?
Jan 19 No Colloquium (MLK day)
Jan 26 Cancelled (snow)


Feb 2 Manfred Cuntz (U. Texas at Arlington) - Habitability Around Single Stars and in Multiple Stellar Systems
Feb 9 Keivan Stassun (Vanderbilt) - Advances in Stellar Astrophysics, Star Formation, and Exoplanet Science with Large Surveys
Feb 16 No Colloquium (President's Day)
Feb 19 Special Date
Jordan Camp (GSFC) - Detection of Gravitational Radiation from a Merging Black Hole Binary and the New Era of Gravitational Wave Astronomy
Feb 23 Nico Cappelluti (Yale) - Search for signatures of early black holes


Mar 1 Brian McNamara (Waterloo) - Molecular Gas Flows in Cluster Cores Revealed by ALMA
Mar 8 Special Location: B34, W120 A&B
Tracy Slatyer (MIT) - Gamma Rays from the Inner Milky Way: Dark Matter or Point Sources?
Mar 15 Nick Cowan (McGill) - Mapping Exoplanets (and what it's good for)
Mar 22 Kaya Mori (Columbia) - A hard X-ray view of the Galactic Center with the NuSTAR telescopes
Mar 29 Goddard Scientific Colloquium: 3:30 pm; Coffee/Tea at 3:00 pm; Building 3 Auditorium
Ewine van Dishoeck (Leiden) - Where Does the Water in our Oceans Come From?


Apr 5 No Colloquium (HEAD Meeting)
Apr 8 Special Date
Daniel Kocevski (GSFC) - An overview of time-domain astrophysics with Fermi Gamma-ray Space Telescope
Apr 12 Francesco Miniati (Zurich) - MHD Turbulence in Hot Intracluster Medium
Apr 13 Special Colloquium: 12 noon, Room W120A+B
Chiara Mingarelli (Caltech) - The Gravitational-Wave Universe seen with Pulsar Timing Arrays
Apr 19 Colloquium Canceled
Apr 26 No Colloquium


May 3 Tiziana Di Matteo (CMU) - The Next Frontier of High-redshift Quasars and Massive Galaxies
May 10 No Colloquim
May 11 Special Colloquium: 2:00, Room W120 A+B
Lou Strolger (STScI) - High Redshift Supernovae: Beyond The Epoch of Dark Energy
May 12 Special Colloquium: 12:00, Room W150
Jack Burns (Colorado) - Cosmology from the Moon: The Dark Ages Radio Explorer (DARE)
May 17 Special Location: B34, W120 A&B
Shane Larson (NW) - Gravitational Waves (tentative title)
May 24 Cora Dvorkin (Harvard) - Observational Cosmology and Fundamental Physics (tentative title)
May 31 No Colloquium (Memorial day)


Jun 7 James Reeves (Keele) - X-ray Spectroscopy of AGN (tentative title)
Jun 14 John Silverman (Tokyo) - Subaru Deep Surveys (tentative title)

How Can Supermassive Black Holes Drive the Evolution of Entire Galaxies?

Francesco Tombesi


Tuesday, Jan 12, 2016


Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this "quasar mode" feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in an ultraluminous infrared galaxy and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming missions ASTRO-H (launch date early 2016) and Athena (2028).

Habitability Around Single Stars and in Multiple Stellar Systems

Manfred Cuntz

U. Texas at Arlington

Tuesday, Feb 2, 2016


Habitability, i.e., the planet’s potential to develop and sustain life, is a topic of intense research, encompassing both favorable conditions as, e.g., the size and stability of the stellar climatological habitable zones as well as adverse forcings. The latter encompass numerous factors including (but not limited to) intense UV, X-rays, and flares, including superflares, which have the potential of evaporating planetary atmospheres. These constituents apply to both planets around single stars and those hosted by multiple stellar systems. Regarding the latter, the analysis of planetary habitability is, however, more complex as, e.g., the presence of multiple stellar components affects both the extent and time-dependence of the climatological habitable zones and the domains of planetary orbital stability. Recent progress has been made in regard to binary systems, pertaining to both S-type and P-type planetary orbits. Detailed results have been obtained for a large variety of observed and theoretical systems, including systems detected by the Kepler mission. The purpose of my talk is to summarize recent results and to convey perspectives of future research.

Advances in Stellar Astrophysics, Star Formation, and Exoplanet Science with Large Surveys

Keivan Stassun


Tuesday, Feb 9, 2016


Large surveys, such as the Sloan Digital Sky Survey and the upcoming Large Synoptic Survey Telescope, are revolutionizing many areas of astrophysics. I present some recent discoveries that highlight the diversity of advances enabled by large surveys of stars and exoplanet systems, including: (1) that the most and least tightly bound binary star systems likely have a common dynamical origin; (2) that the properties of low-mass stars and of benchmark eclipsing binary systems can be corrupted through the effects of magnetic activity and of tertiary bodies; and (3) that the "flickering" of stars, due to the granulation of their surfaces, reveals the true physical properties of exoplanets. I close with some thoughts on the role of human visualization for discovery with big data.

Detection of Gravitational Radiation from a Merging Black Hole Binary and the New Era of Gravitational Wave Astronomy

Jordan Camp


Friday, Feb 19, 2016


The era of Gravitational Wave Astronomy has begun. On Sept 14 2015 the Laser Interferometer Gravitational Wave Observatory (LIGO) detected gravitational radiation from the last moments of the merging of a Black Hole Binary system. I will describe the detection and its implications, as well as the incredible sensitivity of the LIGO detectors that made the detection possible. I will give some background on the notion of Black Holes since they were first predicted as a consequence of Einstein's theory of General Relativity in 1916. Finally, I will talk about Goddard's role going forward in this highly promising new field of astronomy.

Search for signatures of early black holes

Nico Cappelluti


Tuesday, Feb 23, 2016


Search for the formation mechanism of supermassive black holes (SMBH) requires to access, with X-ray observations, the Universe at z>5. This is a challenge, because the deepest Chandra observations, combined with HST-WFC3, provide only a handful of candidate high-z AGNs that can be used to test the SMBH formation machanisms. Beyond that, we need to search for their footprints in the cosmic backgrounds. I will present recent observational result that may shed light on the first black holes in the Universe. In particular, recently detected joint fluctuations of the Chandra Cosmic X-ray Background and the Spitzer Cosmic Infrared Background are opening a new window on this epoch of the cosmic history and paving the way for JWST, The X-ray Surveyor and Athena.

Molecular Gas Flows in Cluster Cores Revealed by ALMA

Brian McNamara


Tuesday, Mar 1, 2016


Dozens of brightest cluster elliptical galaxies contain molecular gas reservoirs exceeding 10^9 solar masses, fuelling star formation rates of tens of solar masses per year. These galaxies are embedded in hot, X-ray atmospheres where the cooling time falls below one Gyr. The cooling atmospheres are expected to form molecular clouds that fuel star formation and energetic feedback from central supermassive black holes. New observations of a half dozen brightest cluster galaxies obtained with the Atacama Large Millimeter Array are revealing a diversity of molecular gas dynamics and morphologies including, molecular inflow, outflow, and star formation occurring preferentially in filaments rather than in molecular disks. Molecular cloud ensemble velocities generally lie far below the stellar velocity dispersions, indicating their motions are not governed by gravity. I will show that AGN feedback scales with halo mass, and I will suggest that molecular gas fuelling feedback likely cooled in the wakes of buoyantly-rising radio bubbles.

Gamma Rays from the Inner Milky Way: Dark Matter or Point Sources?

Tracy Slatyer


Tuesday, Mar 8, 2016


Studies of data from the Fermi Gamma-Ray Space Telescope have revealed bright gamma-ray emission from the central regions of our galaxy, with a spatial and spectral profile consistent with annihilating dark matter. However, I will present a new model-independent analysis that suggests that rather than originating from dark matter, the GeV excess may arise from a surprising new population of as-yet-unresolved gamma-ray point sources in the heart of the Milky Way. I will briefly discuss other possible explanations, and whether an unexpected new population of millisecond pulsars could be responsible.

Mapping Exoplanets (and what it's good for)

Nick Cowan


Tuesday, Mar 15, 2016


Extrasolar planets are being discovered at an unprecedented rate, and their atmospheres have recently become accessible to remote study. Exoplanets provide excellent laboratories for testing theories in planetary science, but they are so distant that we must contend with disk-integrated observations. I will describe how we extract spatially-resolved images of planets from such data. Current optical and infrared observations give us insight into the compositions, clouds, and heat transport of short period planets. Upcoming direct-imaging missions will monitor the scattered light from exoplanets, allowing us to constrain the obliquity and surface character of rocky worlds. In other words, we will soon be able to construct globes of exoplanets. The atmospheric state and surface character of exoplanets provide leverage to crack hard problems in geoscience, such as cloud formation, wind velocities, and geochemical cycling.

A hard X-ray view of the Galactic Center with the NuSTAR telescopes

Kaya Mori


Tuesday, Mar 22, 2016


In June 2012, the Nuclear Spectroscopic Telescope Array (NuSTAR) was launched into orbit, carrying the first hard X-ray (10-79 keV) focusing telescopes with sub-arcminute angular resolution. One of the major goals of the NuSTAR mission was to conduct a detailed hard X-ray survey of the point sources and diffuse emission around the Galactic Center. The baseline NuSTAR Galactic Center survey, with total area coverage of 0.7 deg^2 and total exposure of 2 Msec, detected 70 hard X-ray point sources, four X-ray transients including a new magnetar SGR J1745-29, and hard X-ray flares from the central supermassive black hole (Sagittarius A*). NuSTAR resolved diffuse features such as previously unknown central hard X-ray emission, molecular clouds and non-thermal X-ray filaments above 10 keV. I will review this survey and highlight some of the important results from NuSTAR's high-resolution imaging and broad-band spectroscopy. I will also discuss some implications for the Galactic Center TeV emission, the origin of thousands of Chandra X-ray point sources, the Galactic Ridge diffuse X-ray emission as well as the on-going NuSTAR Legacy survey program.

Where Does the Water in our Oceans Come From?

Ewine van Dishoeck


Tuesday, Mar 29, 2016


Water is one of the most abundant chemical species in the universe, and essential for the origin of life (as we know it) on Earth and on the many exoplanets that have now been identified. But where does all the water in our oceans come from? Recent observations, in particular with the Herschel Space Observatory, show that molecules such as water are formed in the very tenuous clouds between the stars that are present throughout the entire Milky Way. The latest results on water gas and ice in protostellar sources will be presented and the evolution of water and the oxygen reservoir from clouds to new stars and planets will be discussed, together with predictions for JWST observations. An important clue on how this water is delivered to planetary systems comes from measurements of heavy water, HDO. The Rosetta mission has found surprisingly high values for the HDO/H2O ratio in comet 67 P/C-G. The implications of this measurement for the origin of water on Earth will be discussed.

An overview of time-domain astrophysics with Fermi Gamma-ray Space Telescope

Daniel Kocevski


Friday, Apr 8, 2016


Ongoing observations by NASA's Fermi Gamma-ray Space Telescope have shown that the gamma-ray sky is populated by transient sources whose activity varies on timescale as short as a fraction of a second (gamma-ray bursts, terrestrial gamma-ray flashes, and solar flares), to days (Crab nebula and high-mass x-ray binaries), and even years (blazars). I will review some of the recent discoveries made through Fermi observations of these transient events, ranging from the detection of long-lived high-energy emission from gamma-ray bursts to the flaring of galactic sources previously believed to be quiescent in nature. I will also discuss how our transient detection pipelines are now enabling the search for the electromagnetic counterparts to LIGO gravitational wave detections.

MHD Turbulence in Hot Intracluster Medium

Francesco Miniati


Tuesday, Apr 12, 2016


Galaxy clusters are the largest virialized structures in the cosmic web, serving as unique cosmological probes and laboratory for plasma astrophysics. Most of the cluster mass is in nonbaryonic dark matter, while the majority of the visible matter is in the form of hot, optically thin, turbulent, magnetised and non-maxwellian plasma -- the intracluster medium (ICM). The origin of magnetic field and non-maxwellian tails in the ICM remain unsolved problems. Clusters form through gravitational instability, which causes clusters to merge into larger and larger structures, while driving supersonic accretion flows, large-scale shocks and giant turbulent eddies in the ICM. Dissipation of turbulence partially heats the ICM, but also amplifies magnetic fields via dynamo action. Conversion of gravitational energy into kinetic, thermal, turbulent and magnetic is a fundamental feature of the cluster hydrodynamics.

I will describe a novel high-resolution numerical simulation of a massive Coma-like galaxy cluster in a fully cosmological context, designed to resolve turbulence (Miniati 2014; Miniati 2015; Beresnyak & Miniati 2015). We find that the ICM of massive clusters follows a surprisingly simple self-similar dynamics, in which the ratios of thermal, turbulent and magnetic energies encode the physics of hydro and MHD processes in the ICM.

The Gravitational-Wave Universe seen with Pulsar Timing Arrays

Chiara Mingarelli


Wednesday, Apr 13, 2016


Pulsar Timing Arrays (PTAs) are currently the only way to search for gravitational radiation in the nanohertz band. Sources of interest include gravitational wave (GW) backgrounds generated by supermassive black hole binaries (SMBHBs) and processes in the early universe such as relic GWs and cosmic strings. Limits on the GW background continue to improve, and searches of increasing sensitivity are ongoing. Here I will discuss recent limits on the stochastic GW background, how we can characterize the stochastic GW background from SMBHBs on any angular scale to search for anisotropy, and how environmental interactions with SMBHBs affect the GW strain spectrum, and thus become observable. I then discuss how PTAs can place limits on the amplitude of the relic GW background and may eventually be a valuable tool for cosmology by providing independent constraints on the tensor-to-scalar ratio “r", and the spectral index of the tensor fluctuation spectrum “n_t”. Finally, I present recent NANOGrav limits on cosmic string tension, which are a factor of 4 more constraining than the Planck (2014) results.

The Next Frontier of High-redshift Quasars and Massive Galaxies

Tiziana Di Matteo


Tuesday, May 3, 2016


I will discuss predictions for the first quasars and the first galaxies and their contribution to reionization from the BlueTides simulation. BlueTides is a uniquely large volume and high resolution simulation to study the high redshift universe: with 0.7 trillion particles in a volume of 1/2 of a Gigaparsec on the side. This is the first simulation large enough to resolve the relevant scales that form the first massive galaxies and quasars. These massive objects at high redshifts will be the next frontier for the next generation telescopes (Euclid, JWST, WFIRST).

High Redshift Supernovae: Beyond The Epoch of Dark Energy

Lou Strolger


Wednesday, May 11, 2016


For nearly two decades the Hubble Space Telescope has been heavily used to locate supernovae in high redshift environments, with the primary goal of improving constraints on the nature of dark energy. Along the way we have made surprising observations on the nature of supernovae themselves, and clues to their elusive progenitor mechanisms, some of which are difficult to reconcile with observations at much lower redshift. From complete volumetric supernova rate histories, that for the first time extend to z > 2, we find type Ia supernova delay-time distributions are consistent with a power law of index -1, but with the fraction of prompt (t_d < 500 Myr) much less than expected from various ground-based surveys. Core collapse supernova rates trace the cosmic star formation rate history, but require stellar progenitors more massive than has been seen in deep studies of nearby events (M > 20 M_sol). I will also detail our current campaigns on clusters of galaxies (RELICS and the Frontier Fields), where gravitational lens magnification provides a real potential for locating the first, primordial supernovae, while also providing useful constraints on the mass models of the foreground gravitational lenses.

Cosmology from the Moon: The Dark Ages Radio Explorer (DARE)

Jack Burns


Thursday, May 12, 2016


In the New Worlds, New Horizons in Astronomy & Astrophysics Decadal Survey, Cosmic Dawn was singled out as one of the top astrophysics priorities for this decade. Specifically, the Decadal report asked “when and how did the first galaxies form out of cold clumps of hydrogen gas and start to shine—when was our cosmic dawn?” It proposed “astronomers must now search the sky for these infant galaxies and find out how they behaved and interacted with their surroundings.” This is the science objective of DARE – to search for the first stars, galaxies, and black holes via their impact on the intergalactic medium (IGM) as measured by the highly redshifted 21-cm hyperfine transition of neutral hydrogen (HI). DARE will probe redshifts of 11-35 (Dark Ages to Cosmic Dawn) with observed HI frequencies of 40-120 MHz. DARE will observe expected spectral features in the global signal of HI that correspond to stellar ignition (Lyman-α from the first stars coupling with the HI hyperfine transition), X-ray heating/ionization of the IGM from the first accreting black holes, and the beginning of reionization (signal dominated by IGM ionization fraction). These observations will complement those expected from JWST, ALMA, and HERA. We propose to observe these spectral features with a broad-beam dipole antenna along with a wide-band receiver and digital spectrometer. We will place DARE in lunar orbit and take data only above the farside, a location known to be free of human-generated RFI and with a negligible ionosphere. In this talk, I will present the mission concept including initial results from an engineering prototypes which are designed to perform end-to-end validation of the instrument and our calibration techniques. I will also describe our signal extraction tool, using a Markov Chain Monte Carlo technique, which measures the parameterized spectral features in the presence of substantial Galactic and solar system foregrounds.

Maxim Markevitch
NASA Logo, National Aeronautics and Space Administration