And Then There was Light: What Determines the “Active” Zones of Jets?
September 12, 2019
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
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
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
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
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
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
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.
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
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.
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
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
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
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.
Constraining planetary histories with new architectures: resonant chains and circumbinary orbits
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.
The Galactic Center black hole with GRAVITY
February 14, 2019
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
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
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
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
Cecilia Payne-Gaposchkin Lecture
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
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
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
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
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
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
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
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
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
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
Prospects for unseen planets beyond Neptune
Lecar Prize Lecture
September 13, 2018
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
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
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.
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.
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.