Absorption of the Cosmic Microwave Background (CMB) by the 21-cm Hydrogen Line at Redshift 17
Haystack / MIT
A deeper than expected absorption with flattened bottom has been observed using the Experiment to Detect the Global EoR signature (EDGES) instruments located at the Murchison Radio-astronomy Observatory in Western Australia. I will describe the instrument and its calibration and how the performance has been improved over a period of about 12 years leading to detection of the 21_cm absorption at 78 MHz. Absorption of the CMB is expected when the hydrogen spin temperature drops from the CMB temperature to the kinetic temperature as the result of Wouthuysen–Field coupling of the Lyman-Alpha radiation from the early stars. I will discuss the need and prospects for confirmation by other instruments, the future plans of EDGES, list mechanisms which might explain the greater depth and flattened profile and allow time for discussion of these mechanisms.
The Physics of AGN-driven Galactic Winds
Over the past decade, observations have revealed AGN feedback in action in the form of energetic, wide-angle, galaxy-scale outflows powered by luminous quasars. These outflows are observed at essentially all wavelengths, ranging from the radio to the optical to X-rays, and have raised a number of important theoretical puzzles. For example, the outflows can carry a momentum over an order of magnitude in excess of the AGN radiative output, and a large fraction of the outflowing mass is observed in cold, dense molecular gas moving at highly supersonic velocities up to ~1,000 km/s. In this talk, I will present analytic and numerical models aiming to explain the acceleration and observational properties of AGN-driven galactic winds. I will emphasize recent results on the origin of molecular outflows, including predictions for infrared emission by warm molecular gas that will be testable by the James Webb Space Telescope. I will also summarize on-going efforts to model the effects of AGN winds in galaxy evolution.
The Rise of the Milky Way: Gaia's 3D View of the Local Neighborhood
University of Vienna
Most of what we know about star and planet formation has been obtained from spatial 2D observations of the local Galactic neighborhood (d ~ 1 kpc), collected over the last 70 years. During this time we have built a pragmatic, although simplified, view of the local complexes, establishing a series of ground truths that guide today's star formation research. For example, we use Orion as the template for massive star formation and Taurus for low-mass star formation. We have embraced supersonic turbulence as a fundamental pillar of the star formation process, but have not identified its source. We have organized groups of young stars as either bound clusters or associations and wondered about the origin of an all-sky structure we call Gould’s belt. Recently, we found that this view might be up for revision, as we have seen evidence for a new and more significant arrangement of young massive stars in the local neighborhood we call Blue Streams. These streams appear to be several hundred pc long and display monotonic age sequences, suggestive of a common origin at Galactic scales. If real, Blue Streams would play a critical role in understanding the structure of the local ISM, would give a much-needed context to local star formation, and even allow the prediction of the "galactic weather" our solar system will face in the future. In this talk, a week and a day after Gaia Data Release 2, I will present the very latest from the 3D view of the local neighborhood and will try to validate or reject old and new ideas.
Rosetta at Comet 67P: Deciphering the Origin of the Solar System, the Earth and Life
April 26, 2018
After more than 12 years the Rosetta spacecraft crash-landed on comet Churyumov-Gerasimenko on September 30, 2016. It has traveled billions of kilometers, just to study a small (4 km diameter), black boulder named 67P/Churyumov-Gerasimenko. The results of this mission now seem to fully justify the time and money spent in the last decades on this endeavor. In the talk I will look back on the craziest mission ever flown by the European Space Agency and point out its technical challenges and scientific highlights. I will show how the results of this mission change our understanding about the formation of the solar system, the Earth and finally life itself.
Binary Compact Object Mergers in the Gravitational Wave Era
April 19, 2018
Stony Brook University
The observation of gravitational waves has opened a new, unexplored window onto the Universe. Among the sources of gravitational wave transients, compact objects such as neutron stars (NSs) and black holes (BHs) play the most important role. In this talk, I will focus on the expected gravitational wave signal when two compact objects (NS-NS and NS-BH) in a binary merge. These events are believed to be accompanied by a strong electromagnetic signature in gamma-rays, followed by longer-wavelength radiation. I will discuss what can be learned from the complementary observations of the electromagnetic and the gravitational wave signals during these events.
What Astrobiology Tells Us About The Anthropocene
University of Rochester
In this talk I present new results exploring how questions related to developing a sustainable human civilization can be cast in terms of astrobiology. We begin by presenting a classification scheme for planets based on the degree of chemical disequilibrium generated by the coupled planetary systems. In this context we discuss the role of biospheric feedbacks in the presence of a global energy-harvesting species. We explore how Earth System Science frames the thermodynamics of successful species and their interaction with biospheres including those species that develop energy-intensive civilizations. We then focus on the most import factor for sustainability in an astrobiological context: the mean lifetime L of an ensemble of species with energy-intensive technology. We cast the problem into the language of dynamical system theory and discuss how astrobiological results usefully inform the creation of dynamical equations, their constraints and initial conditions. We present solutions to an initial set of equations showing different trajectories of development of the couple civilization-planetary system. Finally we use Kepler data to set an empirical limit on the probability that we are the only time in cosmic history that an energy intensive technological species has evolved.
Molecules From Clouds to Disks and Planets: Building on Dalgarno's Legacy
Ewine van Dishoeck
The discovery of thousands of planets around stars other than our Sun has revived age-old questions on how these exo-planets form and which chemical ingredients are available to build them. Chemistry starts in the cold and tenuous clouds between the stars. In spite of the extremely low temperatures and densities, these clouds contain a surprisingly rich and interesting chemistry, as evidenced by the detection of nearly 200 different molecules. Examples of recent developments in astrochemistry will be presented, with special emphasis on topics that Alex Dalgarno has opened up (i.e., most of astrochemistry!).
New facilities such as ALMA and soon JWST will allow us to zoom in on dense cloud cores and planetary system construction sites with unprecedented sharpness and sensitivity. Spectral scans of young disks contain tens of thousands of rotational lines, revealing water and a surprisingly rich variety of organic materials, including simple sugars and high abundances of deuterated species. How are these prebiotic molecules formed and can they end up on new planets? A comparison with recent results from the Rosetta mission to comet 67 P/C-G in our own Solar System provides part of the clue. These recent results leave no doubt on the answer to the famous question asked by Dalgarno in 1986 `Is astrochemistry useful?'.
Cosmology With the Hyper Suprime-Cam (HSC) Survey
Carnegie Mellon University
Hyper Suprime-Cam (HSC) is an imaging camera mounted at the Prime Focus of the Subaru 8.2-m telescope operated by the National Astronomical Observatory of Japan on the summit of Maunakea in Hawaii. A consortium of astronomers from Japan, Taiwan and Princeton University is carrying out a three-layer, 300-night, multiband survey from 2014-2019 with this instrument. In this talk, I will focus on the HSC survey Wide Layer, which will cover 1400 square degrees in five broad bands (grizy), to a 5 sigma point-source depth of r~26. We have covered 240 square degrees of the Wide Layer in all five bands, and the median seeing in the i band is 0.60 arcseconds. This powerful combination of depth and image quality makes the HSC survey unique compared to other ongoing imaging surveys. In this talk I will describe the HSC survey dataset and the completed and ongoing science analyses with the survey Wide layer, including galaxy studies, strong and weak gravitational lensing, but with an emphasis on weak lensing. I will demonstrate the level of systematics control, the potential for competitive cosmology constraints, some early results, and describe some lessons learned that will be of use for other ongoing and future lensing surveys.
High-redshift Star Formation Under the Cosmic Microscope
University of Illinois
Recent facilities such as the South Pole Telescope (SPT), the Herschel Space Observatory, and the Atacama Large Millimeter Array (ALMA) have opened a window to the millimeter (mm) sky and revealed a unique and unprecedented view of the dusty Universe. In a 2500 square degree cosmological survey, SPT has systematically identified a large number of high-redshift strongly gravitationally lensed starburst galaxies. We have completed a unique spectroscopic redshift survey with ALMA, targeting carbon monoxide line emission in these sources. We have obtained spectroscopic redshifts for 82 sources, with a median of z=3.9. This sample comprises 70% of the total spectroscopically confirmed starburst and extends into the epoch of re-ionization. We are undertaking a comprehensive and systematic followup campaign to use these “cosmic magnifying glasses” to study the physical conditions and chemical evolution of the dust-obscured universe in unprecedented detail, using ionized carbon, carbon monoxide, and water. These sources are also part of an Early Release Science Program with the James Webb Space Telescope (JWST), due to launch in less than a year. Combined, these images taken with ALMA and JWST will be the most detailed study of the redshift 7 Universe, less than 800 million years after the Big Bang.
ITC Colloquium Eric Keto (CfA)
"Accretion physics in high mass star formation"
ABSTRACT: The accretion flows that form O and B type share similarities with other accretion flows in astrophysics but have some unique characteristics. Accretion flows around type B stars resemble scaled-up flows around lower mass stars although the disks around B stars are massive enough to be self-gravitating. Nonetheless, observations suggest these disks are stable under Toomre's criterion because of their high temperatures of a few thousand degrees. Type O stars are hot enough to significantly ionize their surroundings including their own accretion flows. These stars often form in groups of several O stars close enough together that their combined mass is effectively a point-source with respect to the larger-scale accretion flows of several thousand AU. The combination of the strong inward gravitational and outward pressure forces creates some interesting and perhaps unexpected dynamics. For example, the ultra-compact HII regions that we observe around clusters of O stars are not simply expanding bubbles of ionized gas but an ionized accretion-outflow system. The accretion flows transition inward from molecular to ionized passing supersonically through an ionization front which slows and compresses the flow such that the ionized region is higher density than the molecular. The magnetically-driven bipolar outflows that are found around low-mass stars are not seen, replaced by pressure-driven outflows of ionized gas. Recent ALMA observations suggest new, interesting, and well-defined problems in theoretical astrophysics.
Jupiter Internal Structure and the First Juno Results
Host: Sean Andrews
Observatoire de la Côte d'Azur
The key to understand our origins is in the interiors and atmospheres of the giant planets. Jupiter is the biggest planet in our system and the most influential one: its large mass shaped the architecture of the solar system and due to its fast formation it contains valuable information of the solar system formation history. In orbit since July 2016, the first orbits of the Juno mission have led to a remarkable improvement of the planet gravity data, changing our knowledge of the planetary interior and leading to a much better comprehension of the giant planet and its role in the solar system. In this seminar, I will present the new Juno results, the models we use to understand Jupiter's interior and its differential rotation, and the main challenges and questions that remained to be solved.
pH Lecture: Exoplanet Atmosphere Characterization, Present and Future
in HD 1080p
Exoplanet Atmosphere Characterization, Present and Future
March 1, 2018
We now know that exoplanets abound in the Galaxy, with most stars hosting at least one planet. These recently discovered worlds are much more diverse than the planets in the Solar System, and raise many questions about their formation, evolution, and habitability. To address these questions, we turn to atmosphere characterization, which provides a wealth of additional information about the planets. I will discuss the state of the art in atmosphere studies, focusing on recent high-precision, space-based observations of hot Jupiters and warm Neptunes. These studies have already revealed planetary atmospheric chemistry, climate, and cloud coverage in unprecedented detail, and they are poised for a revolutionary advance thanks to the upcoming launch of the James Webb Space Telescope. I will conclude with a discussion of prospects for future observations with JWST, including the characterization of temperate, terrestrial worlds.
The Virtual Observatory is Very Much Real
In HD 1080p
Host: Alyssa Goodman
Speaker: Giuseppina Fabbiano (CfA)
While the VO is now embedded in the fabric of data astronomy, astronomers are still largely unaware of it, and often think of it as a past, perhaps failed, experiment. Instead, chances are that if you work with data, you are already using the VO. In this talk, I will discuss VO perception and reality, and demonstrate recent VO-enabled software and interfaces. Observations of the sky by means of increasingly powerful ground-based and space telescopes (and simulations) produce a rich and ever larger volume of digital data. They constitute a tremendous Virtual Observatory for astronomers to investigate the properties and evolution of the Universe. The realization that a new infrastructure was needed to fully and easily exploit these increasingly complex, diverse and large data sets, led to the constitution in 2002 of the International Virtual Observatory Alliance (IVOA), the standards organization for digital astronomy data access and interoperability. The IVOA has so far been joined by 21 national and international VO projects worldwide, and has produced standards for finding, accessing, selecting, extracting, analyzing and visualizing data. IVOA standards are increasingly implemented in all the major archives worldwide. Data centers are beginning to be built upon these standards, and new telescope projects are planning to use them. IVOA standards are used in a growing set of popular tools and interfaces in astronomy, as well as in tools used for Education and Outreach world-wide.
Sackler Lecture: Exploration of the Universe with Gravitational Waves
Host: Charles Alcock
The observations of gravitational waves from the merger of binary black holes and from a binary neutron star coalescence followed by a set of astronomical measurements is an example of investigating the universe by “multi-messenger” astronomy. Gravitational waves will allow us to observe phenomena we already know in new ways as well as to test General Relativity in the limit of strong gravitational interactions – the dynamics of massive bodies traveling at relativistic speeds in a highly curved space-time. Since the gravitational waves are due to accelerating masses while electromagnetic waves are caused by accelerating charges, it is reasonable to expect new classes of sources to be detected by gravitational waves as well. The lecture will start with some basic concepts of gravitational waves. Briefly describe the instruments and the methods for data analysis that enable the measurement of gravitational wave strains of 10 -21 and then present the results of recent runs. The lecture will end with a vision for the future of gravitational wave astrophysics and astronomy.
Turbulent Beginnings: A Predictive Theory of Star Formation in the Interstellar Medium
In HD 1080P
Host: Alyssa Goodman
Our current view of the interstellar medium (ISM) is as a multiphase environment where magnetohydrodynamic (MHD) turbulence affects many key processes. These include star formation, cosmic ray acceleration, and the evolution of structure in the diffuse ISM. In this talk, I shall review the fundamentals of galactic turbulence and then discuss progress in the development of new techniques for comparing observational data with numerical MHD turbulence simulations. I shall highlight a number of exciting problems that our statistical, numerical and observational progress in the field of MHD turbulence has opened up to quantitative analysis. In particular, I will demonstrate how the star formation rate can be analytically calculated from our understanding of how turbulence and gravity induced density fluctuations in the ISM via a probability distribution function analysis. This analytic calculation predicts star formation rates from pc size scales (GMCs) to kpc size scales in galaxies. These studies represent just the beginnings of a bright future for research in galactic and extragalactic turbulence.
SPHEREx: An All-sky Infrared Spectral Survey Explorer Satellite
Hosted by Gary Melnick
SPHEREx, a mission in NASA's Medium Explorer (MIDEX) program that was selected for a competitive Phase A in August 2017, is an all-sky survey satellite designed to address all three science goals in NASA's astrophysics division, with a single instrument, a wide-field spectral imager. We will probe the physics of inflation by measuring non-Gaussianity by studying large-scale structure, surveying a large cosmological volume at low redshifts, complementing high-z surveys optimized to constrain dark energy. The origin of water and biogenic molecules will be investigated in all phases of planetary system formation - from molecular clouds to young stellar systems with protoplanetary disks - by measuring ice absorption spectra. We will chart the origin and history of galaxy formation through a deep survey mapping large-scale spatial power in two deep fields located near the ecliptic poles. Following in the tradition of all-sky missions such as IRAS, COBE and WISE, SPHEREx will be the first all-sky near-infrared spectral survey. SPHEREx will create spectra (0.75 – 4.2 um at R = 40, and 4.2 – 5 um at R = 135) with high sensitivity using a cooled telescope with a wide field-of-view for large mapping speed. During its two-year mission, SPHEREx will produce four complete all-sky maps that will serve as a rich archive for the astronomy community. With over a billion detected galaxies, hundreds of millions of high-quality stellar and galactic spectra, and over a million ice absorption spectra, the archive will enable diverse scientific investigations including studies of young stellar systems, brown dwarfs, high-redshift quasars, galaxy clusters, the interstellar medium, asteroids and comets. SPHEREx is a partnership between Caltech, JPL, Ball Aerospace, and the Korea Astronomy and Space Science Institute.
Connecting Protoplanetary Disk and Exoplanet Atmospheric Composition
Univ. of Michigan
In planetary atmospheres equilibrium chemistry will redistribute elements into specific carriers depending on local conditions. Therefore to draw a link between planet formation and end-state composition, we need to measure absolute abundances and trace the bulk carriers of key elements, particularly carbon and oxygen. In this talk I will discuss methods to determine bulk abundances, relative to hydrogen, within protoplanetary disks to provide grounding data on the disposition of elemental C and O during the phase of giant planet formation. Based on surveys of emission lines with ALMA (CO) and Herschel (H2O), one intriguing result is that the main volatile carriers of C and O appear to be missing in gas-rich disk systems. The implication is that either nearly all Myr-old disks are effectively gas-poor (dissipating) or that chemical abundances are lower than expected. We will show that in at least one system resolved ALMA observations of optically thin CO isotopologues and unresolved Herschel observations of water vapor suggest the chemical abundances are reduced in emissive layers. We will present models that support the hypothesis that the missing gas-phase volatiles are present as ices locked within growing dust particles in the disk midplane. In all, we are on the cusp of greater understanding regarding the chemical content of planet-forming disks with important implications for the baseline level of chemical enrichment within giant planet atmospheres.
Cecilia Payne-Gaposchkin Lecture: Reading Physics From Stellar Spectra
How to extract physical information from stellar spectra is a century-old effort,
brilliantly advanced by Cecilia Payne in her thesis. Over the last decade,
the exponential growth in the quantity and quality of stellar spectra has outpaced
the advances in building ab initio models for stellar spectra. Consequently,
much of the information content of stellar spectra in current surveys goes
to waste, both in terms of the kinds of physical quantities to be extracted,
and in terms of precision. I will lay out new ways to read physics from stellar spectra,
and what this is starting to teach us about stars and the Galaxy.
Armed with these interpretive tools, the road ahead leads to SDSS V, whose
all-sky, multi-epoch spectroscopy can genuinely offer to boost a renaissance
in stellar astrophysics.
Galaxy Cluster Evolution over the Past 10 Billion Years
In recent years, the number of known galaxy clusters has grown dramatically, thanks in large part to the success of surveys utilizing the Sunyaev Zel'dovich effect. In particular, surveys like the South Pole Telescope 2500 deg^2 survey have discovered hundreds of distant clusters, allowing us to trace for the first time the evolution of clusters from shortly after their collapse (z~2) to present day (z~0). In this talk, I will highlight recent efforts to understand the observed evolution in the most massive clusters, focusing on the evolving dynamical state of clusters, the evolving metallicity of the intracluster gas, the assembly history of the central giant elliptical galaxy, and the effects of the central supermassive black hole on the evolution of the cluster core. In addition, I will attempt summarize the current state of galaxy cluster surveys and briefly discuss the potential of next-generation surveys.
Joint Detection of Gravity Waves and Light from the Binary Neutron Star Merger GW170817
November 16, 2017
The much-anticipated joint detection of gravitational waves and electromagnetic radiation was achieved for the first time on August 17, 2017, for the binary neutron star merger GW170817. This event was detected by Advanced LIGO/Virgo, gamma-ray satellites, and dozens of telescopes on the ground and in space spanning from radio to X-rays. In this talk I will describe the exciting discovery of the optical counterpart, which in turn led to several detailed studies across the electromagnetic spectrum. The results of the observations carried out by our team include the first detailed study of a "kilonova", an optical/infrared counterpart powered by the radioactive decay of r-process nuclei synthesized in the merger, as well as the detection of an off-axis jet powering radio and X-ray emission. These results provide the first direct evidence that neutron star mergers are the dominant site for the r-process and are the progenitors of short GRBs. I will also describe how studies of the host galaxy shed light on the merger timescale, and describe initial constraints on the Hubble Constant from the combined GW and EM detection.
The SAGA Project: Satellite Galaxy Populations Around Milky Way-like Galaxies
The properties of the Milky Way's satellite galaxies provide critical clues to how galaxies form. However, the number of Milky Way satellites and their properties do not fully agree with well-established cosmological models. The SAGA (Satellites Around Galactic Analogs) survey is a long-term program to determine complete satellite luminosity functions around 100 Milky Way analogs down to Mr = -12. I will present early results from the SAGA survey. Surprisingly, the majority (26/27) of our satellites are star-forming, as compared to 2 of 5 star-forming Milky Way satellites in the same luminosity range. I will discuss how these results potentially change the physical interpretation of measurements based only on the Milky Way's satellites.
The WIMP is Dead. Long Live the WIMP!
October 19, 2017
Although weakly interacting massive particles (WIMPs) have long been the leading class of candidates for the dark matter of our universe, the lack of a confirmed detection of these particles has left the community increasingly skeptical of their existence. In this talk, I will ask the following questions: How surprised should we be that WIMPs have not yet been detected? What assumptions might we change in order to explain the lack of any clear signals of dark matter? In light of the current experimental situation, what are the prospects for future direct, indirect and collider searches for dark matter?
Gas: A Prime Driver of Galaxy Evolution
Great progress has been made over the past two decades in constraining the star formation history of the universe, but our understanding of how cosmic star formation is fueled by molecular gas at high redshift remains limited to specific, and potentially biased samples of galaxies. To overcome these limitations, we have carried out a large blind volume search for molecular gas in galaxies at redshifts 2-3 and 5-7 with the Karl G. Jansky Very Large Array (VLA). This measurement of the "cold gas history of the universe" near the peak of cosmic star formation and in the first billion years of cosmic time provides important information on the fueling mechanisms that drive cosmic star formation. To probe the detailed physical properties of these processes, we augment this survey with in-depth, high-resolution studies of star-forming galaxies back to the earliest epochs with the Atacama Large sub/Millimeter Array (ALMA) and other facilities, from
"normal", low-metallicity galaxies all the way to the most intense, massive dusty starbursts. These studies fundamentally enhance our picture of early galaxy evolution by providing a better understanding of the stellar mass buildup, and they provide detailed constraints on the design of planned galaxy surveys in the early universe with the next generation Very Large Array (ngVLA).
The Dynamics of the Local Group: Challenges to Convention in the Era of Precision Astrometry
Bok Prize Lecture:
Univ. of Arizona
Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. I will provide an overview of key contributions by the Hubble Space Telescope to this evolving picture. In particular, I will highlight the impact of the HSTPROMO team’s proper motion measurements of key players in the Local Group, such as the most massive satellites of the Milky Way (the Large and Small Magellanic Clouds), the first direct proper motion measurement of M31 and an implied new orbital history for M33. These results have met with controversy, challenging preconceived notions of the orbital dynamics of key components of the Local Group. They also make concrete predictions and have profound implications for our analysis of upcoming high-precision astrometric data from e.g., Gaia, LSST and JWST.
Constructing The Glass Universe
Constructing The Glass Universe
October 5, 2017
I will talk about my process for conceptualizing, researching, and writing a work of narrative non-fiction.
Three Puzzles in Star and Planet Formation
September 28, 2017
Univ. of Arizona
In the past 5 years, new observational facilities have provided remarkable data sets against which we can evaluate theories of star formation and planet formation. I will describe three different theoretical investigations motivated or corroborated by new observations. In each case, important open questions remain. First I will discuss the formation of close binaries through a variety of channels. I will illustrate how ALMA and careful statistical studies have begun to validate a long-held theoretical picture. Next, I will discuss the surprising high resolution ALMA images of protoplanetary disk asymmetries. I will show how careful numerical models can validate (or not) the interpretation of these images as evidence for the Rossby Wave Instability. Finally, I will discuss the dynamics of the Pluto-Charon circumbinary satellite system. The New Horizons space mission not only provides new insights into the formation of these bodies, but also provides a record of the Kuiper Belt and thus planet formation in the outer solar system.
Quasars as New Standard Candles
The Evolution of the Milky Way Disk
September 14, 2017
Ohio State University
The past 10 billion years have been an exciting time for the Milky Way's disk. Based on over 100,000 stars with SDSS/APOGEE near-infrared spectra, I will review work on its age distribution, both radially and vertically, and the evidence for radial mixing of populations. I will present work on the large-scale chemical cartography of the Milky Way disk. I will discuss current efforts to calibrate "chemical age" indicators, in particular C/N in red giants, using stellar cluster data and asteroseismic ages. I will conclude with the most ambitious program yet to study the Milky Way disk -- the ~5 million star Milky Way Mapper, part of the After-Sloan-IV proposal.
The Golden Anniversary of Very High Energy Gamma-ray Astronomy
Fifty years since construction of its first observatory commenced in 1967, the field of Very High Energy gamma-ray astronomy has truly entered a golden age. Astrophysicists using third-generation facilities such as VERITAS have grown the VHE source catalog to hundreds of sources, and a world-wide consortium of approximately 1400 scientists are poised to begin construction of a $400 million, next-generation VHE gamma-ray observatory (CTA) in 2018. Clearly there were many causes for celebration as VERITAS, the world’s most sensitive VHE gamma-ray observatory completed its tenth season of operation in July 2017. Highlights from the past decade of the VERITAS scientific program will be presented. In addition, an overview of CTA and the latest news concerning its development, including the potential US contribution, will be discussed.
Clay Fellowship Lecture: Chemical Evolution of Galaxies
The chemical evolution of the Universe is governed by star formation and flows of gas in and out of galaxies. I will discuss the chemical evolution history of galaxies measured from the strong emission lines observed in the spectra of galaxies. I will develop a theoretical framework to interpret the measurements and show how the data combined with theory provide powerful constraints for understanding star formation and gas flows on cosmological scales.
Host: Charles Alcock
Speaker: Harus Jabran Zahid
A New Measurement of the Expansion Rate of the Universe
The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was possible with the first generations of Hubble Telescope instruments. A streamlined distance ladder constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provide 2.4% precision and offer the means to do much better. By steadily improving the precision and accuracy of the Hubble constant, we now see evidence for significant deviations from the standard model, referred to as LambdaCDM, and thus the exciting chance, if true, of discovering new fundamental physics such as exotic dark energy, a new relativistic particle, or a small curvature to name a few possibilities. I will review recent and expected progress.
Host: Daniel Eisenstein
Speaker: Adam Reiss
Fast Radio Bursts -- Nature's Latest Cosmic Mystery
Fast Radio Bursts are millisecond-duration pulses of unknown origin that were discovered by pulsar astronomers in 2007. A decade on from the discovery, with only 20 further bursts currently known, fast radio bursts remain enigmatic sources which parallel the early days of gamma-ray burst astronomy in the early 1970s. I will tell the story of their discovery, summarize what we know about them so far, describe the science opportunities these bursts present, and make predictions for what we will learn in the next decade.
Host: Peter Williams
Speaker: Duncan Lorimer
pH Lecture: The Universe’s Largest Particle Accelerators
Galaxy clusters are the largest gravitationally bound objects in our Universe and are unique laboratories to study fundamental questions in astrophysics. Galaxy clusters grow by mergers with smaller subclusters and galaxy groups. In this talk, I will discuss how merging galaxy clusters can act as giant particle accelerators, producing extremely energetic cosmic rays.
Host: Charles Alcock
Speaker: Reinout van Weeren
Superluminous Supernovae: Extreme Explosions in Dwarf Galaxies
The new generation of wide-field optical time-domain surveys has revealed an unexpected diversity in supernovae. Most surprising of all is the discovery of hydrogen-poor superluminous supernovae, which are brighter than the explosions of other massive stars by a factor of ~100, but less common by a factor ~10^4 and seemingly confined to faint, low-metallicity galaxies. I will review the unique properties of these events and the suggested explosion mechanisms, and show how recent observations are converging towards a consistent explanation of the power source. I will briefly motivate further the study of these objects through their suitability for high-redshift studies with upcoming space missions, and whether this could open a new window in supernova cosmology. Finally, I will demonstrate how the distinctive dwarf galaxies that host superluminous supernovae connect these events with long-gamma ray bursts and perhaps even fast radio bursts, suggesting that FRBs may track the birth rate of millisecond magnetars in low-metallicity environments.
Host: Dan Milisavljevic
Speaker: Matthew Nicholl
Heavy Element Enrichment in Early Circumgalactic and Intergalactic Environmnents
Robert Simcoe (MIT)
Lecar Prize Lecture: Kepler's Exoplanet Legacy & the Passing of the Baton
The scientific community recently celebrated two decades of exploring the diversity of planets and planetary systems orbiting main sequence stars. Today, the discoveries spill into the thousands, and the sensitivity boundaries continue to expand. NASA's Kepler Mission unveiled a galaxy replete with small planets including populations that don't exist in our own solar system. The final discovery catalog and the associated survey completeness and reliability metrics will be delivered this spring as Kepler (prime) heads toward mission closeout on September 30, 2017. The final data products are sufficient for computing planet occurrence rates as a function of size, orbital period, and host star properties. To date, we've learned that every late-type star has at least one planet, that terrestrial-sized planets are more common than giants within 1 AU, and that the nearest, potentially habitable earth-sized planet is likely within 5 pc.
After four years of continuous data collection, Kepler prime ceased observations of Cygnus/Lyra in May 2013 when a second reaction wheel failed. Thanks to innovative engineering, the spacecraft gained a second lease on life and emerged as the ecliptic surveyor, K2. In many regards, K2 is a distinctly new mission, not only by pointing at new areas of the sky but also by focusing on community-driven goals that diversify the science yield. For exoplanets, this means targeting bright (V 13) and low mass (M dwarfs) stars -- the populations harboring planets amenable to dynamical and atmospheric characterization. To date, the mission has executed 12 observing campaigns lasting ~80 days each and has achieved a 6-hour photometric precision of 30 ppm. Nearly 150 new planets have been confirmed, including nearby ( 50 pc) systems on the watch-list for future observing campaigns with the James Webb Space Telescope.
While Kepler prime is setting the stage for the direct imaging missions of the future, K2 is easing us into an era of atmospheric characterization with TESS and JWST. We are ready to pass the baton to these future missions taking us one step closer toward finding evidence of life beyond the Solar System.
Host: Matt Holman
Speaker: Natalie Batalha (NASA Ames Research Center)
Black Holes in Globular Clusters
Host: Charlie Conroy
Speaker: Jay Strader - Michigan State University
Hundreds of stellar-mass black holes form in the early lifetime of a typical globular star cluster. But, unlike the case for neutron stars, no bright X-ray binaries containing black holes have been observed in globular clusters, which led to theoretical predictions that most or all of the black holes should be efficiently ejected through dynamical interactions. I will highlight results from our ongoing survey using deep radio continuum and X-ray data to search for accreting black holes in Milky Way globular clusters, presenting evidence that black holes may indeed be common in globular clusters. I will discuss implications for the dynamical formation of binary black holes observable as LIGO gravitational wave sources.
The MOSFIRE Deep Evolution Field (MOSDEF) Survey
A detailed census of the physics of galaxy formation in the early universe
Alice Shapley (UCLA)
Neutron Star Binary Mergers in the Era of Gravitational Wave Astronomy
Host: Edo Berger
Speaker: Brian Metzger
The discovery of coalescing binary black holes by Advanced LIGO heralds the birth of a new field of research: gravitational wave (GW) astronomy. Coalescing neutron star (NS) binaries are among the new GW sources expected over the next few years. Maximizing the knowledge gained from this discovery will require identifying a coincident electromagnetic counterpart. One promising counterpart is an optical/IR flare, powered by the radioactive decay of neutron-rich elements synthesized in the merger ejecta (a so-called `kilonova'). Beyond providing a beacon to the GW chirp, kilonovae probe one of the dominant astrophysics sites for creating the heaviest elements in the Universe via rapid neutron capture (r-process) nucleosynthesis. I will describe how the lifetime of the hypermassive NS created during a NS-NS merger impacts the light curves and color of kilonovae, and how this affects the ongoing strategy of LIGO electromagnetic follow-up. A small fraction of short gamma-ray bursts are accompanied by long-lived X-ray emission, which may suggest that some mergers result in the formation of long-lived - or even indefinitely stable - NS remnants. If this association is confirmed, this would place stringent constraints on the equation of state of nuclear density matter.
Galaxies at Cosmic Dawn
Exploring the First Billion Years with Hubble and Spitzer and the Implications for JWST
U.C. Santa Cruz
Solar Flares - How the Sun Relaxes
Host: Edward DeLuca
Speaker: Lyndsay Flectcher (University of Glasgow)
The outer atmosphere of the Sun is a magnetically-dominated environment. The magnetic field determines the transport, storage and dissipation of energy, in fairly steady ways (coronal heating, solar wind acceleration) but also in abrupt and impulsive events called solar flares. Solar flares represent the rapid conversion of energy as the magnetically stressed corona relaxes, with magnetic energy going into plasma heating, the KE of accelerated particles and mass motions. Flares are now observed in exquisite detail with imaging and spectroscopy across the electromagnetic spectrum, allowing increasingly meaningful comparisons with detailed theory. In this talk I will give a general overview of recent flare observations and the framework in which they are interpreted, before focusing on one aspect of flare physics, namely the need to rapidly transport energy through the corona and accelerate particles. I will also place our knowledge of solar flares in the context of what we are learning about stellar flares.
Gravitational Wave Detection with Advanced LIGO
Matthew Evans (MIT)
New Frontiers in Microlensing
The field of microlensing was pioneered as a method to find dark matter in the form of MACHOs but was rapidly repurposed as a planet-finding technique. The quest to find and characterize planetary signals has driven the field to high-cadence wide-field surveys and to space. I will review two exciting developments in microlensing: microlensing parallaxes with Spitzer, which probe the distribution of planets as a function of galactic environment, and the Korea Microlensing Telescope Network, which permits continuous monitoring of microlensing events to search for planets beyond the snow line. These projects are revolutionizing all aspects of the field of microlensing from the search for planets to the detailed characterization of complex lensing systems.
Speaker: Jennifer Yee (Harvard-Smithsonian Center for Astrophysics)
Host: Andrew Szentgyorgyi (CfA)
Project Starshot: Visiting the Nearest Star Within Our Lifetime
The nearest star to the Sun, Proxima, was discovered this year to host an Earth mass planet in its habitable zone. Proxima is only 4.24 light years away. Can a camera fly by this planet to find out whether there is life on it? Starshot is a new project aimed to develop the technology that will enable to launch a spacecraft at a fifth of the speed of light, so that it will reach Proxima within our generation. The concept is based on a high power (100GW scale) laser beam pushing a lightweight (gram scale) sail, attached to a chip containing a miniaturized camera, communication and navigation devices. The feasibility study phase of the project had just started at a funding level of $100M for the next 5-10 years, with CfA participation.
Speaker: Avi Loeb
Host: Charles Alcock
The Hydrogen Epoch of Reionization Array
Chris Carilli (NRAO)
James Moran (CFA)
CfA Colloquium: Models of Black Hole Accretion
Charles Gammie (University of Illinois)
How Cosmology Grew, 1916 to 2016 Sackler Lecture
Speaker: James Peebles (Princeton University)
Host: Charles Alcock
Pluto Revealed! Latest Results from NASA's New Horizons Mission
Speaker: Richard Binzel (MIT)
Host: Mark Gurwell
Gravitational Wave Astrophysics: The Future is Now
Ilya Mandel - University of Birmingham
Introduction by James Guillochon
A Modest Perspective On Heterotic String Theory & Implications For Astronomy
S. James Gate (University of Maryland)