Astrophysics Science Division Colloquium Series
Schedule: Spring 2017

Astrophysics Science Division Colloquium Series
Schedule: Spring 2017

Recent schedules:

  2017, Spring  
2016, Fall 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 10 Special Location: B34, W120
Alex Gianninas (Oklahoma) - "Searching for Galactic Gravitational Wave Sources"
Jan 17 No Colloquium
Jan 23 Special Date
Michael Fall (JHU) - "Galaxy formation: simpler than it looks"
Jan 30 Special Date
Richard Mushotzky (UMD) - "Results from Hitomi - the Perseus Cluster and a Little Bit More"


Feb 7 Special Location: B34, W120
Alberto Bolatto (UMD) - "Gone with the Wind? A Close Look at a Starburst-Driven Molecular Galaxy Outflow"
Feb 14 Neil Gehrels Memorial Colloquium. Speakers will include Neil's friends and colleagues.
Feb 15 Special Date
Kohta Murase (PSU) - "High-Energy Cosmic Particle Mysteries"
Feb 21 No Colloquium
Feb 28 Alan Dressler (Carnegie Obs.) - "Star Formation and Structure in Galaxies: Is Density Destiny?"


Mar 7 Daniel Eisenstein (Harvard University) - "Dark Energy and Cosmic Sound"
Mar 14 Feryal Ozel (Arizona) - "A New Era of Compact Objects"
Mar 21 Chuck Bennett (JHU) - "All Things Considered: Fresh Air on Cosmology in the Here and Now"
Mar 28 Special Location: B34, W120
Norbert Langer (Bonn) - "The Stellar Eddington Limit"


Apr 3 Special Date & Location: B36, C211
Kelly Holley-Bockelmann (Vanderbilt) - "Building the Black Hole in Our Own Backyard"
Apr 11 Massimo Cappi (Bologna) - "The Athena X-ray Observatory: scientific objectives and mission study"
Apr 18 Duncan Farrah (Virginia Tech) - "Insights into galaxy assembly from luminous AGN in the distant Universe"
Apr 25 Special Location: B34, W120
Benjamin Williams (U Washington) - "The Panchromatic Hubble Andromeda Treasury"


May 2 Doug Finkbeiner (Harvard) - "Mapping dust in 3D with stellar colors"
May 9 Special Location: Building 8 Auditorium
Rainer Weiss (MIT) - Bahcall Lecture - Observation of the merger of binary black holes: the beginning of gravitational wave astronomy
May 16 Chris Carilli (NRAO Socorro) - "The Next Generation Very Large Array"
May 23 Brian Fields (Illinois) - "When Stars Attack! Confirmation, Identification, and Localization of a Recent Near-Earth Supernova"
May 30 No Colloquium


Jun 6 Lev Titarchuk (Ferrara University) - "Signatures of extragalactic Black Holes and their comparison with Galactic ones"
Jun 13 Leo Singer (GSFC), "New LIGO results (tentative)"


Jul 27 Special Date
Toru Tanimori (Kyoto University) - "Imaging spectroscopy in MeV gamma-rays, and how to attain a 1 mCrab sensitivity for MeV all-sky survey"

Searching for Galactic Gravitational Wave Sources

Alex Gianninas


Tuesday, Jan 10, 2017


Given the age of the Universe, low mass stars have not yet had enough time to evolve off the main sequence to form extremely low-mass (ELM) white dwarfs. Thus, the only way to form ELM white dwarfs, with masses M < 0.3 M_sol, is through evolution in ultra-compact binary systems. The ELM Survey is a targeted spectroscopic survey aimed specifically at discovering and characterizing ELM white dwarf binary systems, all of which have orbital periods of less than a day. These binary systems are of interest because of their eventual merger products which could include Type Ia and underluminous supernovae. Of possibly greater importance is the process by which these white dwarfs will merge as their binary orbits are expected to decay via the emission of gravitational waves. Indeed, several ELM white dwarf binaries are among the best and loudest gravitational wave verification sources for LISA, the European Space Agency's planned space-borne gravitational wave detector. Finally, I will also discuss the increasing number of known pulsating ELM white dwarfs. The study of these pulsations, via asteroseismology, can help constrain pulsar spin-down rates, ELM white dwarf evolutionary models and provide a unique tool to probe the internal structure and physics of ELM white dwarfs.

Galaxy formation: simpler than it looks

Michael Fall


Monday, Jan 23, 2017


This colloquium focuses on some aspects of galaxy formation that are remarkably simple. The talk includes theory, observation, and simulation, and is aimed at a general astrophysics audience. The starting point is a description of galaxies in terms of their most basic physical properties: mass, scale radius, and rotation velocity, or equivalently, mass, gravitational energy, and angular momentum. This description and some simple theory leads to a physical explanation for the formation of galaxies of different morphological types (aka the Hubble Sequence). Some other highlights of the colloquium are the following: (1) The morphologies of galaxies are closely related to their specific angular momenta. (2) Disk-dominated galaxies have about the same specific angular momenta as their dark-matter halos; spheroid-dominated galaxies have about five times less. (3) Feedback by young stars (stellar radiation and winds, supernovae, etc) and active galactic nuclei is crucial for understanding the angular momenta of galaxies and hence their morphologies and hence the Hubble sequence. (4) The relations between the specific angular momenta and sizes of galaxies and their halos are nearly constant over the redshift range 0 < z < 3. Galaxies and their halos grow together nearly homologously.

Results from Hitomi - the Perseus Cluster and a Little Bit More

Richard Mushotzky


Monday, Jan 30, 2017


Before the tragic loss of the spacecraft, the Soft X-ray Spectrometer on the Hitomi/Astro-H observatory observed the Perseus cluster of galaxies, producing X-ray spectral data with unprecedented spectral resolution and sensitivity. I will briefly review the scientific impact of these transformation data on our understanding of cluster physics and the central active galaxy as well as Hitomi observations of the three other objects for which Hitomi data were obtained, the Crab Nebula, G21.5 and N132D.

Gone with the Wind? A Close Look at a Starburst-Driven Molecular Galaxy Outflow

Alberto Bolatto


Tuesday, Feb 7, 2017


Galactic winds, due either to massive star formation or to active galactic nuclei, are one of the favored mechanisms necessary to regulate star formation activity and explain several aspects of present-day galaxies. In particular "cold" galactic winds, where the main ejecta are atomic or molecular, enable the cycling of large amounts of matter in and out of galaxies and provide explanation to a number of observations. Our understanding of how gas is launched and how much mass is involved in these winds is, however, rudimentary. I will present observations of the archetypal nuclear starburst galaxy NGC 253 by ALMA and HST, and show how we are starting to decipher the launching processes and mass loss rates in this example of a starburst-driven galaxy wind. Specifically, I will motivate the importance of the topic and discuss our observations of the morphology, mass, and acceleration of material in the molecular outflow.

High-Energy Cosmic Particle Mysteries

Kohta Murase


Wednesday, Feb 15, 2017


New frontiers of particle astrophysics have been opened by IceCube's discovery of high-energy cosmic neutrinos. Their origin is a new mystery in the field, and solving this problem may enable us not only to understand the physics of astrophysical sources but also to obtain important clues about old mystery, the origin of cosmic rays, and to utilize neutrinos as probes of neutrino properties, dark matter, and fundamental physics. In this talk, I summarize the latest results of IceCube observations, and emphasize the relevance of multi-messenger approaches. I will review recent basic ideas on the origin of high-energy cosmic neutrinos, including the grand-unified model we recently proposed, and some implications for particle physics properties.

Star Formation and Structure in Galaxies: Is Density Destiny?

Alan Dressler

Carnegie Obs.

Tuesday, Feb 28, 2017


Our study of galaxies at redshift 0 < z < 1 finds wide variations in star formation histories (SFHs), suggesting that a galaxy's stellar mass does not grow in lockstep with its dark matter halo. Over a factor of 100 in total mass, we find SFH diversity that can be described by two timescales: the epoch of peak star formation, and the time required to form most of the stellar mass. In contrast to expectations from the conformal "grow and quench" picture, we find galaxies as massive as the Milky Way or M31 that formed most of their stars since redshift z=1. The full range of SFHs are found over a total mass range of ~30, reminiscent of how galaxy morphology also shows mass dependence, but the basic morphologies are found a mass range of two orders of magnitude. These behaviors may be best understood as the result of early trajectories for stellar mass growth and galaxy structure that are driven by mass-density differences very early in galaxy formation.

Dark Energy and Cosmic Sound

Daniel Eisenstein

Harvard University

Tuesday, Mar 7, 2017


I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature at a variety of redshifts. I will review our recent work on the theory and practice of the acoustic oscillation method, describe our latest cosmology results from SDSS-III on the expansion history of the Universe, and introduce the upcoming Dark Energy Spectroscopic Instrument (DESI) project.

A New Era of Compact Objects

Feryal Ozel


Tuesday, Mar 14, 2017


The discovery of many diverse populations of neutron stars and black holes is happening at an accelerating rate. The computational advances in calculating the properties of these compact objects, their multiwavelength observations, and the new avenues of studying them with gravitational waves have led to a new understanding of their formation, evolution, and of the fundamental physics that shapes their characteristics. In this talk, I will describe these parallel advances and show how this multi-faceted approach helps pin down our understanding of the evolution of massive stars, supernova explosions, and coalescing compact objects.

All Things Considered: Fresh Air on Cosmology in the Here and Now

Chuck Bennett


Tuesday, Mar 21, 2017


Major stories in the New York Times and Science magazine have recently highlighted tensions in modern cosmological measurements. So have recent talks at Goddard. I will explore the measurement techniques and the data they produce and examine the areas of tension in detail. I will also examine potential modifications to the standard six parameter Lambda CDM cosmological model. Finally, I will also discuss some upcoming experimental steps in observational cosmology.

The Stellar Eddington Limit

Norbert Langer


Tuesday, Mar 28, 2017


The well-known Eddington limit for stars is thought to correspond to the maximum luminosity which a star may have in hydrostatic equilibrium. We show that in our galaxy, non-rotating hydrogen-burning stars above 40 Msun reach or even exceed this limit, while rotating stars do so at even lower mass. Stellar models show that these stars do not become unstable, but inflate their radius. We discuss the observational evidence for this picture, its relation to the truely unstable so called Luminous Blue Variable stars and to dynamical pulsations, and derive consequences for massive single and binary star evolution and for the early stages of supernova explosions.

Building the Black Hole in Our Own Backyard

Kelly Holley-Bockelmann


Monday, Apr 3, 2017


Astronomers now know that supermassive black holes are a natural part of nearly every galaxy, but how these black holes form, grow, and interact within the galactic center is still a mystery. In theory, gas-rich major galaxy mergers can easily generate the central stockpile of fuel needed for a low mass central black hole 'seed' to grow quickly and efficiently into a supermassive one. Because of the clear theoretical link between gas-rich major mergers and supermassive black hole growth, this major merger paradigm has become a well-accepted way to form the billion solar mass black holes that power bright quasars in the early universe. It's much less clear, though, how well this paradigm works for growing the 'lightest' supermassive black holes; these million solar mass black holes tend to lie in galaxies like our own Milky Way, where the supermassive black hole is currently quiescent and major mergers were few and far between. This talk will touch on some current and ongoing work on refining our theories of black hole growth for this lightest supermassive class.

The Athena X-ray Observatory: scientific objectives and mission study

Massimo Cappi


Tuesday, Apr 11, 2017


Athena is a large X-ray Observatory proposed to address the Science Theme “The Hot and Energetic Universe”, which has been selected by ESA in its Cosmic Vision program. After reviewing its core science goals, the astrophysics and cosmic evolution of large-scale hot structures and black holes in the Universe, and (some of) its Observatory capabilities, I will present the mission telescope and instruments, to be implemented as a Large mission planned for launch in 2028.

Insights into galaxy assembly from luminous AGN in the distant Universe

Duncan Farrah

Virginia Tech

Tuesday, Apr 18, 2017


There is a deep connection between star formation and active galactic nuclei which profoundly impacts the assembly history of galaxies across most of the history of the Universe. The nature of the connection however remains controversial, due to, for example, the uncertain evolution in, and synergy between, the AGN and starburst duty cycles, and the obscuring effect of dust. In this talk I will briefly review our current knowledge of galaxy assembly, and then discuss two recent results. First is an observed scaling relation between star formation rates and AGN luminosities in luminous type 1 quasars at high redshift, as determined using data from the Herschel and Spitzer space telescopes. This relation offers insights into how star formation is triggered and quenched in luminous quasars, and how stellar mass assembly proceeds in AGN hosts towards the end of te AGN duty cycle. Second is a study, using both Herschel and HST, on the most luminous obscured AGN in the Universe. The nature of these AGN offers extremely stringent tests of galaxy evolution models. I will discuss the morphologies of their host galaxies, and show that they signpost a brief but critical phase in galaxy evolution.

The Panchromatic Hubble Andromeda Treasury

Benjamin Williams

U Washington

Tuesday, Apr 25, 2017


I will present results from the Hubble Space Telescope multi-cycle PHAT survey. Using over 400 HST pointings, we have resolved and measured over 100 million stars in Andromeda at ultra-violet, optical, and infrared wavelengths. I will review the wide variety of science coming out of the program, including star cluster formation, dust content, halo structure, star formation history, the initial mass function, and more. The varied applications of the data set are leading to several follow-up programs, including similar HST observing programs for other Local Group galaxies, and multi-wavelength observations of M31.

Mapping dust in 3D with stellar colors

Doug Finkbeiner


Tuesday, May 2, 2017


Dust emission maps have long been used to estimate total reddening, integrated along the line of sight. These 2D maps are not adequate for reddening estimates within the Milky Way, where the object of interest may be in front of some of the dust. Using colors of 800,000,000 stars from 2MASS and Pan-STARRS, we can now infer the location of reddening along each line of sight in about 30 distance bins, making a crude 3D dust map with ~ 5 arcmin angular pixels. I will describe our publicly available map from 2015, and show improvements in the 2017 version. I will also argue that reddening-based dust maps are superior for certain cosmological applications because they do not include contamination from the FIR emission from large-scale structure.

Observation of the merger of binary black holes: the beginning of gravitational wave astronomy

Rainer Weiss


Tuesday, May 9, 2017


After some history of gravitational waves will follow with a description of the waves and the technique for detecting them. Present and discuss the observations and end with a vision for the future of gravitational wave astronomy and astrophysics.

The Next Generation Very Large Array

Chris Carilli

NRAO Socorro

Tuesday, May 16, 2017


Inspired by dramatic discoveries from the Jansky Very Large Array and the Atacama Large Millimeter Array, the astronomy community is considering a future large area radio array: the 'Next Generation Very Large Array' (ngVLA). The ngVLA design entails an interferometric array with 10 times larger effective collecting area and 10 times higher spatial resolution than the current VLA and ALMA, optimized for operation in the frequency range 10GHz to 50GHz, with reasonable performance over 1.2GHz to 115GHz. The ngVLA targets observations at wavelengths between the superb performance of ALMA at submm wavelengths, and the future SKA-1 at few centimeter and longer wavelengths. The ngVLA opens a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission at milliarcecond resolution, as well as unprecedented broad band continuum polarimetric imaging of non-thermal processes. These capabilities are the only means with which to answer a broad range of paramount questions in modern astronomy, ranging from direct imaging of planet formation in the terrestrial-zone, to a quantitative census of the dense gas fueling star formation from the present, back to the first galaxies in the Universe. The ngVLA will also enable novel techniques for exploring temporal phenomena from milliseconds to years. As a specific example, I will highlight recent studies of the evolution of the molecular gas content of galaxies, in particular from the ASPECS large program on ALMA. These results demonstrate the progress in our understanding of the evolution of the fuel for star formation in galaxies, as well as accentuate the limitations to such studies that can only be overcome through a telescope like the ngVLA. I will present the current design and parameter space, and the process of community studies driving design specifications.

When Stars Attack! Confirmation, Identification, and Localization of a Recent Near-Earth Supernova

Brian Fields


Tuesday, May 23, 2017


Supernovae are major engines of nucleosynthesis, and create many of the elements essential for life. Yet these awesome events take a sinister shade when they occur close to home, because an explosion very nearby would pose a grave threat to Earthlings. We will show how radionuclides produced by supernovae can reveal nearby events in the geologic past, and we will highlight isotopes of interest. In particular, geological evidence for live 60Fe has recently been confirmed globally in multiple sites of deep-ocean material, in cosmic rays, and in lunar samples (!). We will review astrophysical 60Fe production sites and show that the data demand that one or more core-collapse supernovae exploded near the Earth ∼ 3 Myr ago, and explain how debris from the explosion was transported to the Earth as a “radioactive rain.” The 60Fe measurements represent a new tool: sea sediments and lunar cores as telescopes, probing supernova nucleosynthesis and possibly even indicating the direction towards the event(s). The ~ 1 Myr measured duration of 60Fe deposition is surprisingly long, likely pointing to dust dynamics and evolution effects within the Local Bubble. We will conclude by showing how the 60Fe gradient on the Moon could help localize the explosion site.

Signatures of extragalactic Black Holes and their comparison with Galactic ones

Lev Titarchuk

Ferrara University

Tuesday, June 6, 2017


I will present details of observations of Galactic and extragalactic Black Hole (BH) sources, interpreting the results in the light of first principles theory of X-ray spectral formation. I will also show that, in the BH case, this theory predicts the spectral index vs. mass accretion rate correlation, with the spectral index which increases and then saturates with the mass accretion rate. This spectral index-mass accretion rate correlation allows us to estimate BH masses and distance to the source. Using RXTE, Suzaku, ASCA, BeppoSAX and Swift observations, I will present new results on spectral signatures of different types of BHs, like Ultra Luminous X-ray sources (ULXs) such as M101 ULX-1 and ESO 239-HLX1, and Active Galactic Nuclei (AGN) such as BL Lacertae (B2200+420). Moreover, I will show new exciting results on spectral properties of Tidal Disruption Event (TDE) sources and possibility to estimate BH masses in these sources.

Imaging spectroscopy in MeV gamma-rays, and how to attain a 1 mCrab sensitivity for MeV all-sky survey

Toru Tanimori

Kyoto University

Thursday, July 27, 2017


Since the discovery of nuclear gamma-rays, its imaging has been limited to pseudo-imaging, such as Compton Camera (CC) and coded mask. Pseudo-imaging does not keep physical information (intensity, or brightness in the optical) along a ray, and thus is capable of no more than qualitative imaging of bright objects. To attain quantitative and high-sensitive imaging, cameras that realize geometrical optics are essential, which would be only possible via complete reconstruction of the Compton process. Recently we have revealed that "Electron Tracking Compton Camera" (ETCC) provides a well-defined Point Spread Function (PSF). Information of the incident gamma-ray is kept along a ray with the PSF and that is equivalent to geometrical optics. In addition, we present an imaging-spectroscopic measurement with the ETCC, which highlights the intrinsic difficulty with CCs in performing accurate imaging. The capability of imaging spectroscopy enables to suppress the noise level dramatically, by ~3 orders of magnitude, without a shielding structure, similarly to an X-ray telescope, while keeping a large field of view (>3 sr). A simple extension of the ETCC technology indicates that ETCC with a PSF of ~2 deg and a 1 m^3 gas volume would reach a sensitivity beyond 1 mCrab in MeV region. We will launch a 30 cm^3 ETCC, with a better sensitivity than COMPTEL, on a JAXA one-day balloon flight at Aric Spring in 2018, to measure the 511 keV gamma rays from the Galactic center (SMILE-II+ project).

Maxim Markevitch
NASA Logo, National Aeronautics and Space Administration