Molecular characterization of preserved tissues in a Cretaceous ankylosaur
We used geochemical techniques to study the chemistry of soft tissues of an extraordinarily well-preserved Cretaceous dinosaur from Alberta, Canada. Analysis of the skin and armor plates revealed aspects of the pigmentation and the steroids present in the gut contents showed evidence of the prior presence of a microbiome. This talk will address the evidence that allowed us to make these assessment and other instances where steroids present in hominin guts can provide knowledge of value to archaeologists and health scientists.
The discovery of pulsars - a graduate student's tale
In this talk I will describe how pulsars were accidentally discovered, and reflect on several instances where they were 'nearly' discovered. I will highlight the implications for new telescopes with high data rates.
Bok Prize Lecture: Measuring Spins of Stellar-Mass Black Holes with X-ray Spectroscopy
February 6, 2020
Center for Astrophysics | Harvard & Smithsonian
Abstract: One of the most remarkable properties of an astrophysical black hole is that it can be completely described by just its mass and spin. Knowledge of spin is fundamental for testing how black holes form, for testing the production of relativistic jets, for producing GRBs, and more. X-ray techniques measure black-hole spin by measuring the inner radius of the accretion disk, which corresponds to the innermost stable circular orbit (ISCO). I will describe the foundation of these measurements and summarize our progress, highlighting where we stand 15-years into the field, having achieved a census comprised of several dozen black holes in our Galaxy and Local Group. This talk is dedicated to the memory of Jeff McClintock, whose vision and indomitable curiosity drove him to discover all that could be known about a black hole.
Justin Casper - First Discoveries by Parker Solar Probe and the SWEAP Investigation
The chemical structure of planet forming disks: the story of Nitrogen
What sets the composition of nascent planets is a fundamental question in astronomy, and one that is extremely timely considering the large number of exoplanets with very different characteristics that have been discovered in the past years. Whether these planets can host life depends directly on the composition and distribution of the gas where they form, i.e. protoplanetary disks. Thanks to ALMA we can now image the emission of key organic species at scales of ~15 au. In this talk I will show recent ALMA observations of HCN, one of the simplest but bright N-bearing species in disks, and of its two isotopologues. HCN is of particular interest as it is thought to be the starting point for the formation of the precursors of RNA and proteins. Moreover, the N isotopic ratio 14N/15N is often used to determine the origin of the material in our solar system. However, the 14N/15N ratios varies dramatically between different solar system bodies, and the cause of this variation remains a mystery. I will then comment on the most complex N-bearing species detected in disks so far, and conclude by discussing our current efforts to constrain the chemical structure of disks in the planet and comet forming zone.
Decoding the Milky Way galaxy
Stars orbiting in the Milky Way halo comprise only 1% of our Galaxy's stellar mass. However, these stars are among the oldest in the Galaxy, and thanks to their long relaxation times, they preserve a historical record of the Milky Way forming. To access this historical memory of the halo, we need to measure the precise 3D positions, 3D velocities, and chemical abundances of large numbers of stars. Thanks to the Gaia mission, 5D positions are now available for almost 2 billion stars. In this talk, I will present first results from spectroscopic surveys that use Gaia data to preferentially target halo stars, and have so far mapped the full 6D phase-space for 70,000 stars. I will first discuss how a blind halo survey can be used to discover even the oldest, completely dissolved, progenitors of the Milky Way because they remain distinct in the space of conserved orbital quantities. The abundance and chemical properties of the Milky Way progenitors will provide a unique window into the early universe. Then, I will show how similar observations targeted at a known, cold stellar stream, suggest it recently had a close encounter with a massive and dense perturber, and also constrain the perturber's orbit and present-day location. Known baryonic objects are unlikely perturbers based on their orbital properties, but observations permit a low-mass dark-matter subhalo as a plausible candidate. This observation opens up the possibility that detailed studies of stellar streams could measure the mass spectrum of dark-matter substructures and illuminate the nature of dark matter.
The Galactic Center Gamma-Ray Excess: A Puzzle at the Heart of the Milky Way
The region around the Galactic Center contains a well-characterized excess of gamma rays, which has garnered great interest as a possible signal of either dark matter particles colliding and annihilating, or a previously undiscovered population of pulsars in the stellar bulge. Analyses of the photon statistics of this excess have been used to argue that the pulsar interpretation is strongly favored -- however, I will present recent work arguing that it may be premature to exclude a dark matter origin for the excess on these grounds. I will outline the history of our understanding of the excess and the arguments for various interpretations, describe the current status of the controversy, and discuss future paths forward
Planets in a bottle: Exploring planetary atmospheres in the lab
From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles of "haze". With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed abundances of smaller, gas phase molecules, are not well suited for investigations of much larger, solid phase particles. Laboratory investigations of haze formation in planetary atmospheres therefore play a key role in improving our understanding of the formation and composition of haze particles. I will discuss a series of experiments aimed at improving our understanding of the physical and chemical properties of planetary atmospheric hazes on Titan, Pluto, super-Earths, and mini-Neptunes.
Hubble’s Panchromatic Comparative View of Exoplanet Atmospheres
1080P - 60
Host: Mercedes Lopez-Morales Speaker: David Sing (STScI) Abstract: To date, Hubble has played the definitive role in the characterization of exoplanet atmospheres. From the first planets available, we have learned that their atmospheres are incredibly diverse. With HST, JWST, and TESS a new era of atmospheric studies is opening up, where wide scale comparative planetology is now possible. Such studies can provide insight into the underlying physical process through comparative studies. Hubble’s full spectroscopic capabilities are now being used to produce the first large-scale, simultaneous UVOIR comparative study of 20 exoplanets ranging from super-Earth to Neptune and Jupiter sizes. With full UV to infrared wavelength coverage, an entire planet’s atmosphere can be probed simultaneously and with sufficient numbers of planets, it will be possible to statistically compare their features with physical parameters. The panchromatic treasury program aims at build a lasting HST legacy, providing the UV and blue-optical exoplanet spectra which will be unavailable to JWST, providing key insights into clouds and mass loss. I will review the highlights of the program to date, which include atmospheric water resolved in emission and new absorption features seen in transmission such as escaping ionized metals. I will also present the latest findings from the ongoing Hubble Treasury program and discuss synergies with JWST.
Blast from the Past: Ultraviolet Investigations of Exoplanet Systems and their Habitability
Roughly seventy-five billion low-mass stars (a.k.a. M dwarfs) in our galaxy host one or more small planets in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. In fact, superflares occur daily in their first ~100 Myr, and these effects are amplified by the extreme proximity of their HZs. Understanding the UV environments of M dwarf planets is crucial to understanding atmospheric composition and evolution, and providing context for measured exoplanet spectra. For HZ terrestrial planets, characterization of the UV provides a key parameter in a planet’s potential for habitability as well as for discriminating between biological and abiotic sources of observed biosignatures. Our efforts to study the stellar UV span past, present and future space telescopes: the Galaxy Evolution Explorer (GALEX), the Hubble Space Telescope (HST), and the upcoming NASA-funded Star-Planet Activity Research CubeSat (SPARCS), due for launch at the end of 2021. SPARCS will be a 6U CubeSat completely devoted to continuous photometric monitoring of M stars, measuring their variability, flare rates and evolution, while also being a pathfinder for much-needed future UV missions.
Planck results, curiosities and tensions in the LCDM model
Planck is an ESA satellite aimed at the observation of the Cosmic
Microwave Background. The Planck collaboration has recently published
its last legacy release. In this talk I will shortly review the main
Planck results and their robustness, highlight some of the curious
features present in the data and the Planck point of view on tensions
with a few other astrophysical probes, notably with the Hubble constant
measurements from local distance measurements.
So What's All This Fuss About Decadal Surveys?
Astronomers have been doing decadal surveys for more than half a century. There must be good reasons that our community keeps spending so much time and energy on these reports every ten years. And yet, some in our community have suggested that the whole enterprise has outlived its usefulness and should be rethought. This talk will briefly review the history of the surveys, examine how the reports are used (or not) by policymakers and lobbyists in Washington, and look forward to what we might expect when Astro2020 hits the streets.
The comets that orbit other stars
I will talk about recent work on the small bodies that orbit other stars. We see the dust produced in collisions between these bodies as debris disks, and the large bodies when their comae transit their host stars. A few comet transits have now been detected in broadband space-based photometry, and I will outline the first efforts towards these discoveries. These new detections are complimented by prior transient calcium absorption features, and I will show how the acceleration of these lines provides new constraints on the orbits of the transiting bodies around beta Pictoris. Finally, I will show some new detections of warm dust towards Sun-like stars, and discuss why these detections suggest comets as a probable dust source.
Core-Collapse Supernova Explosions in 3D
October 10, 2019
Abstract: Using our state-of-the-art code Fornax we have simulated the collapse and explosion of the cores of many massive-star models in three spatial dimensions. This is the most comprehensive set of realistic 3D core-collapse supernova simulations yet performed and has provided very important insights into the mechanism and character of this 50-year-old astrophysical puzzle. I will present detailed results from this suite of runs and the novel conclusions derived from our new capacity to simulate many 3D, as opposed to 2D and 1D, full physics models every year. This new capability, enabled by this new algorithm and modern HPC assets, is poised to transform our understanding of this central astrophysical phenomenon.
Chandra's Sharp View of the X-ray Sky: 20 years and counting.
NASA's Chandra X-ray Observatory is celebrating 20 years of operation in 2019. Chandra's uniquely sharp X-ray vision has resulted in major strides in our understanding of all kinds of celestial sources, and it continues to be an indispensable tool for expanding the frontiers of our knowledge. From the discovery of an X-ray jet in its first targeted source and finding the compact stellar remnant of a supernova in the second, the excitement and surprises continue. Chandra uniquely pinpoints the youngest stars buried amongst the gas and dust of star-forming regions, observes the explosions as massive stars run out of fuel and tracks the evolution of the resulting supernova remnants, measures the complex structure of the hot gas which dominates the baryonic matter in clusters of galaxies, tracing their turbulent past and present, explores the properties of dark matter, and observes the matter being captured by black holes of all sizes. I will review highlights of Chandra and its scientific discoveries, from launch on the shuttle Columbia commanded by Eileen Collins, the first female commander, to recent work such as Chandra's first X-ray detection and continued monitoring of GW170817, the merging neutron stars detected in gravitational waves by LIGO.
From Birth to Chirp - Astrophysics of Massive Stars as Gravitational Wave Progenitors
How did they form?’ is a question many asked when LIGO announced the first direct detection of gravitational waves originating from two surprisingly heavy stellar-mass black holes. With masses of about 30 solar masses each, they outweighed all of the known black holes known from X-ray binaries. Now, four years after the first detection, alerts of new triggers come in at a rate of almost one per week. The analysis of the first eleven events has been published and we learned that the first system was not exceptional: the majority of detected events involve heavy black holes. In parallel, classical telescopes have been revolutionizing our understanding of the properties of young massive stars. One of the most remarkable findings is that the majority of massive stars have one or more companions so close that the exchange of mass between them in inevitable during their lifetime. Yet, only a very tiny fraction of these stellar couples are still with their companion after both ended their lives to leave behind a neutron star or black hole. What does it take for a `stellar marriage’ to be such that not even death can part them? I will address some of the exciting new insights, but also the challenges and open questions that we are still facing. More generally I will argue that improving our understanding of massive stars is crucial for a variety of problems in astrophysics. This is because massive stars played a disproportionally large role in transforming the pristine Universe left after the Big Bang into the rich and diverse Universe in which we live today. The fact that we ourselves are largely made of the nuclear ashes of massive stars, makes the quest to understand their lives and deaths an integral part of our quest to understand our own cosmic origin.
The Puzzle of Multiple Populations in Globular Clusters
September 19, 2019
Liverpool John Moores University
Andrea Dupree and Ivan Cabrera
Abstract: Globular clusters (GCs) exhibit star-to-star variations in specific elements (e.g., He, C, N, O, Na, Al) that bear the hallmark of high-temperature H-burning. These abundance variations can be observed spectroscopically and also photometrically, with the appropriate choice of filters, due to the changing of spectral features within the band pass. This phenomenon is observed in nearly all of the ancient GCs, and has recently been found in many younger clusters as well. Many scenarios have been suggested to explain this phenomenon, with most invoking multiple epochs of star formation within the cluster; however, all have failed to reproduce various key observations. I will review the state of current observations and outline the successes and failures of some of the main proposed models. The traditional idea of using the stellar ejecta from a first generation of stars to form a second generation of stars, while conceptually straightforward, has failed to reproduce an increasing number of observational constraints. I conclude that the puzzle of multiple populations remains unsolved, hence alternative theories are needed, and will present new HST results that suggest that we may be finally closing in on origin of this enigmatic phenomenon.
And Then There was Light: What Determines the “Active” Zones of Jets?
September 12, 2019
Abstract: The energy release from black holes is a well-known problem of keen interest to many astrophysics sub-fields, from high-energy astroparticle physics to cosmology and galaxy evolution. For instance we know from the mismatch between ‘gastrophysics-free’ cosmological simulations and observations of the largest scales of structure, that black holes manage to communicate with regions well beyond their gravitational sphere of influence, and that outflows (particularly jets for the largest scales) must be the mechanism. We also know that black holes of all scales experience cycles of activity where the dominant form of energy output changes, and that jet-dominated phases are associated with the highest energy particle acceleration. The problem currently lies in tying all these phenomena together and being able to uniquely predict outflow properties as a function of accretion and environmental properties. In this talk I will discuss a problem I have been puzzling over for some time, which is the link between event-horizon scales and the particle acceleration that “lights up” the jets we observe, which relates to our ability to connect recent Event Horizon Telescope images to observations at other wavebands. In particular I will focus on some recent studies about an older problem well-known in ‘AGN circles’, but that is now being explored in real-time using transient jets from black hole X-ray binaries (BHXBs): what sets the so-called “dissipation zone” where the inner jets start to radiate? I will then discuss how these results can be used to inform our models of both EHT images, and help connect them to the multi-wavelength observations we perform each campaign, as well as increase our understanding of the source of ultra-high energy cosmic rays, TeV gamma-rays and neutrinos.
Reverberation Mapping Black Hole Accretion Discs
September 5, 2019
Abstract: Accreting supermassive black holes can produce more electromagnetic and kinetic luminosities than the combined stellar luminosity of an entire galaxy. Most of the power output from an Active Galactic Nucleus is released close to the black hole, and therefore studying the inner accretion flow is essential for understanding how black holes grow and how they affect their surrounding environments. In this talk, I will present a new way of probing these environments, through X-ray reverberation mapping, which allows us to map the gas falling on to black holes on microparsec scales and measure the effects of strongly curved spacetime close to the event horizon. I will give an overview of the field and present new results from the NICER observatory of unprecedented reverberation measurements in accreting black hole X-ray binaries.
The Event Horizon Telescope: Seeing the Unseeable
May 23, 2019
Science Center A
Abstract: The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array operating at the shortest possible wavelengths, which can resolve the event horizons of the nearest supermassive black holes. Observing at mm radio wavelengths enables detection of photons that originate from deep within the gravitational potential well of the black hole, and travel unimpeded to telescopes on the Earth. The primary goal of the EHT is to resolve and image the predicted ring of emission formed by the photon orbit of a black hole and to eventually track dynamics of matter as it orbits close to the event horizon. A sustained program of improvements to VLBI instrumentation and the addition of new sites through an international collaborative effort led to Global observations in April 2017: the first campaign with the potential for horizon imaging. After 1.5 years of data reduction and analysis we report success: we have imaged a black hole. The resulting image is an an irregular but clear bright ring, whose size and shape agree closely with the expected lensed photon orbit of a 6.5 billion solar mass black hole. This talk will cover the project and first results as well as some future directions.
Searching Near and Far: Transits and Transients from TESS
May 16, 2019
Mercedes Lopez Morales
Abstract: Successfully launched in April 2018, the Transiting Exoplanet Survey Satellite (TESS) is well on its way to discovering thousands of exoplanets in orbit around the brightest stars in the sky. During its two-year prime survey mission, TESS will monitor more than 200,000 bright stars in the solar neighborhood for temporary drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey will identify planets ranging in size from Earth-sized to gas giants, orbiting a wide variety of host stars, ranging from cool M dwarfs to hot O/B giants. TESS stars are typically 30–100 times brighter than those surveyed by the Kepler satellite; thus, TESS planets are far easier to characterize with follow-up observations. For the first time it will be possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. An additional data product from the TESS mission is its full frame images (FFIs) with a cadence of 30 minutes. These FFIs provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the TESS cameras. In total, nearly 100 million objects brighter than magnitude I= +16 will be precisely photometered during the two-year prime mission. As TESS’s limiting magnitude for stacked FFIs extends to fainter than I= +19, we anticipate the discovery of a wealth of galactic and extragalactic transients during the prime mission, as well as numerous asteroids and NEOs. The initial TESS all-sky survey is well underway, covering 13 observation sectors in the Southern Ecliptic Hemisphere in Year 1, and 13 observation sectors in Year 2. A concurrent deep survey by TESS of regions surrounding the North and South Ecliptic Poles will provide prime exoplanet targets for characterization with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes coming online in the next two decades. The status of the TESS mission after the first ten observation sectors will be reviewed. The opportunities enabled by TESS’s unique lunar-resonant orbit for an extended mission lasting more than a decade will also be presented.
Clay Fellowship Lecture : Fast Radio Bursts
In the last decade, we have established the existence of extragalactic fast radio bursts (FRBs) of sub-millisecond durations, likely originating at cosmologically significant distances. Explaining the FRB phenomenon has proved a compelling challenge to theory, with the number of distinct models only this year being superseded by the 65 reported events. The high FRB occurrence rate (comparable to the core-collapse supernova rate), isotropic-equivalent luminosities comparable to the most luminous quasars, the wide range of intrinsic and propagation-induced phenomenology, and the repetition of at least a sub-sample of objects are particularly noteworthy. FRBs have also opened a powerful new window into otherwise unseen matter in the Universe. Observations of large FRB samples will help assess the baryon contents and physical conditions in the hot/diffuse circumgalactic, intracluster, and intergalactic medium, and test extant compact-object dark matter models. I will review the state of the field and its promise for the future.
Implications of Reionizing the Universe with Low Galaxy Escape Fractions
May 2, 2019
Abstract: The reionization of the intergalactic medium (IGM) was the last major phase transition of the universe, and both the time evolution and spatial variation of this process encode key information about the onset of luminous objects in the universe. While we think that massive stars within star-forming galaxies provide the needed ionizing photons, the observed escape fractions of these photons are too low to complete reionization when combined with typical assumptions. We have devised a new semi-empirical model, utilizing simulation-predicted escape fractions (where only the smallest halos have large escape fractions) in combination with observed galaxy luminosity functions. Using physically motivated priors on the threshold for star-formation based on halo mass rather than a single limiting magnitude, and allowing the ionizing photon production efficiency to evolve as suggested by observations, we find that it is possible for reionization to be completed by z=5.5 with low (5%) average ionizing photon escape fractions. Our model makes a number of testable predictions, including: 1) AGNs contribute non-negligibly to the end of reionization, 2) the neutral fraction at z~7 is only 20%, and 3) significant star-formation must be occurring at z~9-10. I will show observational results from my group at UT Austin testing all of these assumptions, including results from ultra-deep Keck spectroscopy for Lyman-alpha emission at z~7-10, and the discovery of several remarkably bright galaxy candidates at z 9. I will finish by discussing how early observations from JWST will further test these predictions, leading to a much better understanding of how early galaxies formed, and began the reionization process.
Stellar Winds with ALMA
April 25, 2019
Abstract: The deaths of stars are always preceded by more or less massive stellar winds. In the case of low- to intermediate mass stars, these winds are the means by which material from the stars is recycled in galaxies. Accurate measurements of the wind physical properties provide constraints for hydrodynamical models which study wind formation and evolution. Estimates of wind density and temperature also form the base for any further research into abundances of different elements, isotopes and molecules in the recycled material. Furthermore, to determine wind gas-to-dust mass ratios holds the key to investigations of extragalactic objects and the impact of these common stars across the Universe. We have lately performed detailed studies of the circumstellar envelopes (CSEs) around nearby (500 pc) stars on the Asymptotic Giant Branch (AGB) with ALMA. The properties of the wind which has created the CSE, can be derived by mapping the CO line emission. We started with a smaller sample of binary stars to investigate the formation and importance of circumstellar asymmetries and structure. To interpret the complex observations, several new analysis tools had to be assembled and tested. These tools are now put to use for the DEATHSTAR project in which we are mapping all nearby AGB stars starting in the southern sky. The goals are to provide the most accurate AGB wind properties to date, and to consistently determine the gas-to-dust mass ratios. I will present results and current status.
Characterizing Terrestrial Exoplanets for Habitability and Life
April 18, 2019
Abstract: One of the most exciting and interdisciplinary frontiers in exoplanet science is the search for habitable planets and life beyond the solar system. Recently discovered planets, especially Earth-sized planets orbiting nearby M dwarfs, will provide intriguing near-term targets for large ground-based telescopes and the James Webb Space Telescope, while even larger telescopes are planned to directly image and explore the environments of worlds around stars like our Sun. These telescopes may detect signs of habitability and its loss, as well as biosignatures—planetary features that suggest a biological origin. However, our ability to accurately interpret these features will depend on our understanding of planetary evolution and processes, and environmental context. This talk will provide an overview of the path to terrestrial exoplanet characterization, describing interdisciplinary research by NASA’s Virtual Planetary Laboratory team to understand how to identify habitable planets, and discriminate true biosignatures from planetary processes, while presenting the prospects for terrestrial exoplanet characterization and life detection with JWST and other future telescopes.
Sackler Lecture: Baryons and Dark Matter in Disk Galaxies
April 11, 2019
Australian National U.
Abstract: The goal is to measure the properties of dark halos of spiral galaxies from the decomposition of HI rotation curves, in order to derive parameters for their dark halos (e.g. the dark matter density and core radius) as a function of galaxy luminosity. Separating the luminous and dark matter components of the rotation curve is an old and degenerate problem. Dynamical estimates of the surface density of the baryonic disk are often been used to break the degeneracy. This usually gives low density submaximal disks with compact dark matter halos that dominate the rotation curve almost everywhere. The surface density of the disk comes from the vertical velocity dispersion and the scale height of the disk: these two parameters must be for the same stellar population. In practice, the scale height is usually for old disk stars, while the measured velocity dispersion is for the combined light of the young and old disk populations. The young stars are bright and kinematically cold, and the combined spectrum leads to an underestimate of the stellar surface density. From high S/N data, it is possible to measure the velocity dispersion of the old hot disk without contamination from the young cold disk. Two dynamical tracers are used for some large nearby spirals: high resolution integrated light spectra of the stellar disk, and velocities of several hundred individual disk planetary nebulae. The two tracers agree well, and give maximal disk surface densities. This validates our approach to the scaling laws for dark halos, which showed how the halo density and core radius scale with luminosity. The halo density gives an estimate of the assembly time of halos of different masses. The baryon content of dwarfs indicates that halos with circular
velocities below about 40 km/s are almost completely dark. (Based on work with J. Kormendy, S. Aniyan, M. Arnaboldi, O. Gerhard et al.)
Mars Climate and Chemical Evolution: Lessons from the Solar System for Exoplanets
April 4, 2019
Abstract: The current era of planetary atmospheric research is characterized by a divide between the solar system, where data is rich but the number of objects to be studied is small, and exoplanets, where data is sparse but the full range of possible states is extremely large. Paleoclimate research is an essential tool with which to bridge this gap, because it allows us to see the present-day surface environments of Earth, Mars and Venus as mere snapshots of nonlinear systems that have evolved significantly over time. Here, I focus on Mars as a case study to show how this approach can yield important insights in practice. Mars has abundant evidence for intermittent habitable conditions in its first gigayear of evolution, but the theoretical explanation for this evidence is a long-standing problem in the field. I discuss how detailed intercomparisons between 3D climate models and the geological evidence have allowed us to gain new insights into the nature of the early Martian hydrological cycle. In addition, new spectroscopic and radiative calculations show that episodic release of reducing gases (H2 and CH4) into Mars’ early atmosphere could have caused intense intermittent warming, potentially resolving the decades-old faint young Sun problem. Based on these insights into Mars’ climate and redox history, we are now developing a greater understanding of exoplanet atmospheric evolution, including the critical question of when gases like oxygen (O2) can be treated as biosignatures.
Bok Prize Lecture: Inner Solar Systems
March 28, 2019
Penn State U.
Abstract: Over the past couple decades, thousands of extra-solar planets have been discovered orbiting other stars. The exoplanets discovered to date exhibit a wide variety of orbital and compositional properties; most are dramatically different from the planets in our own Solar System. Our classical theories for the origins of planetary systems were crafted to account for the Solar System and fail to account for the diversity of planets now known. We are working to establish a new blueprint for the origin of planetary systems and identify the key parameters of planet formation and evolution that establish the distribution of planetary properties observed today. The new blueprint must account for the properties of planets in inner solar systems, regions of planetary systems closer to their star than Earth’s separation from the Sun and home to most exoplanets detected to data. I present work combining simulations and theory with data analysis and statistics of observed planets to test theories of the origins of inner solars, including hot Jupiters, warm Jupiters, and tightly-packed systems of super-Earths. Ultimately a comprehensive blueprint for planetary systems will allow us to better situate discovered planets in the context of their system’s formation and evolution, important factors in whether the planets may harbor life.
The Devil is in the Details
The Devil is in the Details: Using High-Cadence, Multiwavelength Observations to Understand the Disk-Jet Connection in Blazars
March 14, 2019
Abstract: Blazars are active galactic nuclei with relativistic jets that point near the Earth line-of-sight, making them inherently variable sources that are a staple of time-domain and multiwavelength astronomy. This orientation makes them ideal laboratories for studying relativistic jet physics and its interplay with the other AGN components. This talk will review historical and current attempts at disentangling accretion disk and jet emission in these jet-dominated systems —primarily by way of high-cadence, multiwavelength spectroscopic and photometric observations— and build a better understanding of the in/outflow processes of some of Nature’s most powerful particle accelerators. Lastly, I will describe how future instruments can inform blazar studies in the (rapidly approaching) LSST era.
New Simulations and Observations of Highly-Complex Molecules in Star-Forming Regions
March 7, 2019
Abstract: The interstellar medium is replete with molecules, and high-mass star-formation regions in particular are host to some of the most complex organic molecules yet detected outside of our solar system. Millimeter/sub-millimeter wavelength spectral data from the ALMA telescope allows us to explore the chemistry of such regions in much greater detail than ever before. The ALMA 3mm line survey EMoCA ("Exploring Molecular Complexity with ALMA") of the chemically-rich Galactic Center source Sagittarius B2(N) has not only identified several new molecules in that source, but has led to the identification of new molecule-rich hot cores - a total of five are now known to exist in Sgr B2(N). I will give a brief overview of the molecular detections made by EMoCA toward Sgr B2(N). I will also present chemical kinetics models of the coupled gas-phase and grain-surface/ice-mantle chemistry occurring in Sgr B2(N) related to these molecules, with a discussion of our treatment of the recently-detected branched carbon-chain molecule iso-propyl cyanide (i-C3H7CN). I will also present recent work that uses complex molecule abundances to constrain the cosmic-ray ionization rates and chemical timescales within different hot cores. Comparison of observational molecular emission-line strengths with simulated values based on a grid of chemical models indicates that the cosmic-ray ionization rate appropriate to the chemistry of the four hot cores tested is somewhat higher than the canonical value. The same model grid also suggests much shorter chemical timescales than are typically adopted in such models. The CR ionization rates and chemical timescales also appear to have well-behaved relationships with visual extinction and core mass, respectively. Wide-ranging observations of COM abundances, when combined with detailed physical/chemical modeling, may therefore be a powerful indicator of important physical/dynamical conditions that are otherwise inaccessible.
The Exploration of 2014 MU69 by New Horizons
February 28, 2019
Abstract: After traveling for more than 12 years, NASA’s New Horizons mission flew past the cold classical Kuiper Belt Object, 2014 MU69 from a distance of 3500 km. The data returned to the ground reveals that MU69 is a contact binary. There is distinct albedo variation with a high albedo at the connection between the two lobes of this object. We recorded observations with our complete instrument suite and the initial results will be presented. Also, the challenges of carrying out a flyby at a distance of 43 AU at a target that was discovered less than 5 years before the encounter. Event Status:
Constraining planetary histories with new architectures: resonant chains and circumbinary orbits
Abstract: Besides discovering thousands of planetary systems orbiting other stars, one of the legacies of NASA's Kepler mission is the discovery of new planetary architectures. Systems of up to seven planets have been found with orbital periods near integer ratios, librating in three-body resonances. These features point to disk migration into their current orbits and a history of tidal dissipation in the planets over the lifetime of the star. Separately, gas giant planets have been found in orbit around binary star systems, at a location just barely stable against dynamical ejection. Such a location would have been hostile to formation, whereas disk migration models readily explain them. With further study, and with a wider statistical sample from missions such as TESS, these two new architectures will help us validate the physics of planet-disk interactions. Event Status:
The Galactic Center black hole with GRAVITY
February 14, 2019
Abstract: The Galactic Center offers the rare possibility to quantitatively test general relativity in the so-far unexplored regime close to a massive black hole. Here we present the main results from the last two years of GRAVITY observations: the detection of the gravitational redshift in the orbit of the star S2, and the detection of orbital motion close to the last stable orbit during a flare. The GRAVITY instrument, which we have developed specifically for the observations of the Galactic Center black hole and its orbiting stars, is now routinely achieving ~3 milli-arcsec imaging interferometry with a sensitivity several hundred times better than previous instruments. Its astrometric precision of few ten micro arcseconds corresponds to only few Schwarzschild radii of Galactic Center massive black hole, which opens up the possibility to test the fundamentals of gravity all the way from the underlying equivalence principles, to considerations on new physics and their characteristic scales and strengths.
Protoplanetary Disks and Their Dynamic Host Stars
We know that many pre-main-sequence stars are surrounded by protoplanetary disks, but how these disks evolve into planetary systems is a fundamental question in Astronomy. Young stars and their disks are known to be remarkably variable, but it is not clear how this variability may influence planets as they are forming. This talk will review key observations of protoplanetary disks and their young stars, focusing on multi-wavelength variability. To conclude, I will discuss possibilities for future progress in time-domain studies of these young systems.
Linking the Scales of Star Formation
U.Mass, Amherst Understanding galaxy evolution requires understanding star formation and its dependence on the local environment, spanning the scales from individual stars to kiloparsec–size structures. The physical conditions within galaxies determine the formation of stars, star clusters, and larger structures, and their subsequent evolution. HST observations of external galaxies have enabled the characterization of the young stellar populations with unprecedented accuracy and detail, thus aiding the census and description of those populations. These observations are being used to quantify the spatial distribution and clustering of young stars, and investigate the impact and imprint of the physical conditions of both the local and global environment on the formation and evolution of the multi-scale structures. I will concentrate mainly on the results of the Legacy ExtraGalactic UV Survey (LEGUS), an HST Treasury programs that is investigating these issues using multi-color imaging, from the near-UV to the I, of a sample of nearby galaxies. I will also briefly introduce successor programs that promise to expand our understanding of star formation on galactic scales.
The Importance and Challenges in Assessing Stellar Feedback
The Ohio State University
Abstract: Massive stars have a profound astrophysical influence on the interstellar medium (ISM) throughout their tumultuous lives and deaths. Stellar feedback occurs through a variety of mechanisms: radiation, photoionization heating, winds, jets/outflows, supernovae, and cosmic-ray acceleration. Despite its importance, stellar feedback is cited as one of the biggest uncertainties in astrophysics today, stemming from a need for observational constraints and the challenges of considering many feedback modes simultaneously. In this talk, I will discuss recent studies of feedback on ISM scales, from both a theoretical perspective as well as using multiwavelength observations, to understand the comparative role of different feedback modes and how they vary over time and conditions. Additionally, I will present the latest developments in understanding the importance of cosmic-ray feedback, based on simulations and high-energy observations.
Probing the Surfaces of Sun-like Stars Using Transiting Planets and 3D-MHD Simulations
HD1080p/30fps Heather Cegla
Abstract: Our ability to spatially resolve and visually inspect the solar surface makes the Sun the best studied star to date. Even so, the intricacies of many surface phenomena are poorly understood, especially once we move beyond the Sun. Not only will this prevent us from confirming Earth-like planets, but it also limits many areas of stellar physics, such as dynamo theories. In this talk, I will present a new technique to use transiting planets as probes to spatially resolve stellar spectra. With this, we can inspect centre-to-limb variations in the local absorption line profiles shape and net velocity. In turn, this allows us to search for signatures of magnetic activity (e.g. magneto-convection, spots, faculae) and surface differential rotation (as well as determine the star-planet alignment). It also means that, for the first time, we can make detailed comparisons with 3D magnetohydrodynamical simulations of main-sequence stars other than the Sun. We have successfully applied this technique to a G, K, and M dwarf (WASP-8, HD189733, GJ436); for our brightest target, HD189733, we can detect significant differential rotation and confirm good agreement with MHD simulations. For the Sun, we can make more precise centre-to-limb comparisons, and examine the impact of the magnetic field on convective variations. I will also demonstrate how we can use the simulations to predict the relationship between convection-induced line profile shape variations and radial velocities.
Connecting the High Redshift Universe to the Fossil Record
HD 1080p/30fps Cecilia Payne-Gaposchkin Lecture Host:
Abstract: Massive stars provide the most easily observed tracers of the galaxy formation process over the first several billion years of the universe’s history. In addition to being the most likely sources of EUV radiation that reionized the universe at z ~ 7-8, they are responsible for for producing most of the metals that enrich the interstellar, circumgalactic, and intergalactic medium that fuels subsequent generations of stars. Simultaneously, their high luminosities and violent deaths inject large amounts of energy and momentum into their environment, rivaled only by supermassive black holes in the degree to which they affect the galaxy formation process. However, by the present-day, most massive galaxies are long past their historical growth phase, with the bulk of their star formation having occurred in the distant past. Only the integrated population of low-mass stars that formed during a galaxy's peak growth phase remain, comprising a fossil record of the chemical patterns that prevailed during the course of their formation. It is now possible to observe directly the massive star populations in galaxies as they are forming at high redshift (i.e., the ``birth record'') for comparison with the fossil record encoded in the integrated spectra of their present-day descendants. I will argue that massive stars in high redshift galaxies are distinct from those found in any star-forming galaxy at z = 0, and that the differences have important implications for cosmic reionization, the physical interpretation high-z galaxy observations, and understanding the connection to the present-day universe.
New Frontiers in Exoplanet Science with Extremely Precise Doppler Velocimetry
In HD1080p/30fps Host: Martin Elvis
Speaker: Jason Wright (Penn State) Precise radial velocity work, responsible for the lion's share of exoplanet discovery pre-Kepler, remains a cornerstone of exoplanetary research and an essential component of validation and characterization of transiting planets such as those that will be discovered by TESS. It is an important tool for the discovery of long-period planets amenable to direct imaging, determining the architecture of exoplanetary systems, conducting a census of the planetary systems closest to the Sun, and the discovery of new transiting planets including temperate terrestrial planets amenable for atmospheric transmission spectroscopy. This work will be performed by a new generation of extremely precise Doppler spectrographs. In the optical, they will have factors of a few better instrumental precision than the current generation and an order of magnitude below the amplitude of stellar noise ('jitter') in even the quietest stars, which moves the problem of sensitivity from the realm engineering to one of stellar astrophysics and astrostatistics. In the infrared, these instruments will probe new regimes, including terrestrial planets in the Habitable Zones of the coolest, closest stars to the Sun. I will focus on two such instruments built at Penn State, the NN-EXPLORE NEID optical spectrograph which will be a facility instrument at Kitt Peak available for public use, and HPF, an infrared spectrograph at the Hobby-Eberly Telescope focused on work with M dwarf planet hosts.
The Search for Axion Dark Matter
HD1080p/30fps Ben Safdi
Abstract: Dark matter is the dominant source of matter in our Universe. However, while dark matter dictates the evolution of large-scale astrophysical systems through its gravitational effects, the particle nature of dark matter is unknown. This is despite the significant effort that has gone into the search for particle dark matter over the past decades. In this talk I will review the current status of the search for particle dark matter. I will focus specifically on a dark matter particle candidate called the axion, which is both well-motivated theoretically and also relatively unexplored experimentally. I will outline the near-term program for searching for axion dark matter and show that if this theory is correct, then we will probably know soon.
Discovery Frontiers in the New Era of Time Domain Multi-Messenger Astrophysics
HD1080p/30fps Raffaella Margutti
Host: Edo Berger New and improved observational facilities are sampling the night sky with unprecedented temporal cadence and sensitivity across the electromagnetic spectrum. This exercise led to the discovery of new types of astronomical transients and revolutionized our understanding of phenomena that we thought we already knew. In this talk I will review some very recent developments in the field that resulted from the capability to acquire a true panchromatic view of the most extreme stellar deaths in nature.
The Origins Space Telescope: A NASA Decadal 2020 Mission Concept
In HD1080p/30fps Margaret Meixner
Abstract: The Origins Space Telescope (OST) is a low risk, high science impact mission concept that is executable in the 2030’s. OST will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. It will address all three key questions in NASA’s astrophysical roadmap: Are we alone? How did we get here? and How does the Universe work? Specifically, OST will address the questions “How common are life-bearing planets orbiting dwarf stars?”, “How do the conditions for habitability develop during the process of planet formation?” and “How do galaxies form stars, grow their central supermassive black holes, and make heavy elements over cosmic time?” To accomplish its scientific objectives, OST will operate between ~3 to ~600 microns with a JWST sized telescope. Enabled by ~4 K optics and improved detector technology, OST will far exceed previous missions’ sensitivity by up to 1000 times. The observatory has the agility to conduct large surveys and the pointing stability to support pointed observations. The instruments feature improved sensitivity and new spectroscopic capabilities compared to prior or planned missions. This study is one of four science and technology definition studies supported by NASA Headquarters to prepare for the 2020 Astronomy and Astrophysics Decadal Survey.
Planet Formation as Told by Kepler
Karin Öberg and Jane Huang
Abstract: One of the key results from the Kepler mission is that super-Earths and sub-Neptunes abound in the universe, outnumbering their larger counterparts. Their radii (~1--4 Rearth) and masses (~2--20 Mearth) are consistent with the bulk solid-to-gas mass ratio of 100:1. Basic astrophysical considerations of gas dynamical friction, gravitational scattering, collisional mergers, and gas accretion by cooling inform us that these planets likely emerged in situ, in the late stages of disk evolution. The orbital architecture of the planets closest to the star is shaped by the magnetospheric truncation of the disk at stellar co-rotation, and the tidal interaction between the star and the planet. We will show how the theory of star-disk-planet interaction can describe the observed planet occurrence rate as it varies across orbital periods, planet radii, and stellar metallicities.
Fred Whipple’s Empire: The Smithsonian Astrophysical Observatory, 1955-1973
HD 1080p/30fps David DeVorkin
Abstract: In 1955, the Astrophysical Observatory of the Smithsonian Institution in Washington,
D.C., on the south lawn of the Smithsonian Castle, closed and moved as a budget line to the Harvard College Observatory in Cambridge, Massachusetts. Donald Menzel, working in concert with Smithsonian secretary Leonard Carmichael and Harvard dean McGeorge Bundy, encouraged Fred Lawrence Whipple to assume the directorship of the new unit. Initially, Whipple wanted to create an academia-based institutional model for conducting space science in the United States, making his newly minted Smithsonian Astrophysical Observatory a central organizing unit. Instead, after the U.S. government created the National Aeronautics and Space Administration (NASA) to do
just that, Whipple deftly adjusted, building highly competitive programs in astrophysics, space astronomy, geophysics, geodesy, and ground-based optical and radio astronomy. Here I present an overview of how Whipple constructed his empire, first through the expansive era preparing for the International Geophysical Year and then through the early NASA years, creating an astronomical enterprise unlike any the world had seen. I follow his continued ambitions through the late 1960s and into the early 1970s, aided and abetted by a new Smithsonian secretary, S. Dillon Ripley, to examine how his continued efforts resulted in both congressional scrutiny of the Smithsonian and a re-evaluation of the relationship of the Smithsonian Astrophysical Observatory to Harvard and, ultimately, to science in America.
Gaia - The Stereoscopic Survey of the Galaxy
HD 1080p/30fps Gerry Gilmore
Abstract: Astrometry from space has unique advantages over ground-based observations: the all-sky coverage, relatively stable and temperature- and gravity-invariant operating environment delivers precision, accuracy and sample volume several orders of magnitude greater than ground-based results. Even more importantly, absolute astrometry is possible. The European Space Agency Cornerstone mission Gaia is delivering that promise. Gaia provides 5-D phase space measurements, 3 spatial coordinates and two space motions in the plane of the sky, for a representative sample of the Milky Way’s stellar populations (over 1 billion stars, being ~1% of the stars over 50% of the volume). Full 6-D phase space data is delivered from line-of-sight (radial) velocities for the 300million brightest stars. These data make substantial contributions to astrophysics and fundamental physics on scales from the Solar System to cosmology. Deriving full value requires reliable supplementary information, especially on stellar chemical abundances. The Gaia-ESO Public Spectroscopic Survey is an example of such complementary projects, with VLT spectra for 100,000 stars. Gaia-ESO uses very many abundance analysis methods to determine both random and systematic uncertainties in stellar abundances. An overview of Gaia-ESO and some of the challenges in what one can believe will be given.
Title: Stellar UV Light and the Origins of Life
HD 1080P/30fps Dimitar Sasselov
Dave Charbonneau Abstract: I will discuss recent results on the environmental context - astrophysical and planetary,
that makes possible the synthesis of precursor molecules to RNA, peptides, and lipids. My focus
will be on the role of stellar mid-range UV light from about 200 to 300 nm as a source of energy and as a very specific selection agent in chemical evolution.
A Unified Scenario for the Structure, Dynamics, and Star-forming Activity of Molecular Clouds.
HD1080P 30 fps Hierarchical gravitational contraction: a unified scenario for the structure, dynamics, and star-forming activity of molecular clouds.
September 20, 2018
Enrique Vazquez Semadeni
Phil Myers & Qizhou Zhang
Abstract: Diverse numerical and observational evidence suggests that star-forming
molecular clouds (MCs) may be in a process of global gravitational
contraction. As originally proposed by Hoyle (1953), in such a regime, a
sequential destabilization of successively smaller masses should occur,
leading to fragmentation of the cloud and ultimately to the formation of
stellar-mass objects, when the equation of state diverts from
isothermal. After disposing of some early objections to the global
gravitational contraction of MCs, I discuss how this mechanism
naturally explains the observed apparent virialization of clouds and
their substructures, the appearance of Larson's relations when
column-density thresholds are used to define the structures, the
ubiquitous formation of filamentary structures that funnel material to
so-called "hubs", the observed morphology of the magnetic field around
the filaments, the scattered nature of low-mass star-forming regions,
the acceleration of the star formation rate in MCs, the observed
SFR-mass relations at both the local (cloud) level and the global
(galactic) level, and the structure of the embedded stellar
associations, such as their fractal structure and the observed radial
mass and age gradients. I conclude by comparing to the prevailing
"gravo-turbulent" scenario, and note a few common misconceptions about
Lecar Prize Lecture: Prospects for Unseen Planets Beyond Neptune
HD1080P Prospects for unseen planets beyond Neptune
Lecar Prize Lecture
September 13, 2018
Abstract: Recent studies have appealed to anomalies in the orbital distribution of distant Kuiper belt objects to argue for the existence of a roughly Earth-mass planet orbiting at about three times Neptune’s distance and a roughly ten Earth-mass planet orbiting at about twenty times Neptune’s distance. I will review the dynamical structure of the Kuiper belt and the case for the existence of such unseen planets in the distant solar system.
Observing Planet Formation
HD1080P Sean Andrews
Abstract: Planetary systems form in the disks of gas and dust that orbit young stars. In the past few years, very high angular resolution observations of disks in nearby star-forming regions have started to uncover some key signatures of the planet formation epoch. This talk will focus on what we are learning about the distribution of disk material on spatial scales of only a few astronomical units, largely based on state-of-the-art measurements with the Atacama Large Millimeter/submillimeter Array (ALMA), and the corresponding implications for the assembly and early evolution of planetary systems.
Clay Fellowship Lecture: Galaxy Clusters in the Low Frequency Sky
HD1080p Reinout van Weeren (CfA) Hosted: Charles Alcock (CfA) LOFAR is the world’s largest and most sensitive low-frequency radio telescope. It is currently carrying out a monumental survey of the entire northern sky. In this talk I will discuss how we use LOFAR to unravel the physics of particle acceleration and cosmic rays in galaxy clusters, the largest gravitationally bound objects in our Universe.