Pluto Revealed! Latest Results from NASAs New Horizons Mission CfA Colloquium 2016-09-29 | Speaker: Richard Binzel (MIT)Host: Mark Gurwell
Patrick Slane The X-ray Sky in High Definition: Twenty-five Years of Astrophysics CfA Colloquium 2024-10-16 | The X-ray Sky in High Definition: Twenty-five Years of Astrophysics with the Chandra X-ray ObservatoryX-ray astronomy is a product of the space age. Possible only from viewing platforms above the atmosphere, the first celestial X-ray source other than the Sun was discovered just over sixty years ago. Following fresh on the heels of this discovery, with X-ray astronomy just barely in its infancy, an almost unimaginably-bold proposal was put forth to build a visionary space-borne observatory based on X-ray optics whose resolution and sheer size represented leaps by orders of magnitude over any such mirrors ever built. Following a series of smaller, but ever-improving X-ray observatories, this vision was fully realized in July of 1999 with the launch and deployment of NASA's Chandra X-ray Observatory.A quarter century later, Chandra remains the world's premier X-ray astrophysics facility - the crucial high energy component of NASA's fleet of flagship observatories. From resolving the hazy X-ray background into a speckled array dominated primarily by black holes to peering through a gravitational lens to peek at supermassive black hole formation at the edge of time, Chandra has continued to do things that no other X-ray observatory can. It is unique, it ispowerful, and it is healthy - poised to help continue framing the future of high energy astrophysics for years to come. As we celebrate its ongoing success, I will provide a summary of some of the most exciting results from Chandra's ever-increasing scientific legacy, along with a look forward to its continued role as both a unique stand-alone facility and a core element for panchromatic investigations of the Universe.
Adam Burrows The Emerging Panorama of Core-Collapse Supernova Explosion Theory CfA Colloquium 2024-10-09 | The Emerging Panorama of Core-Collapse Supernova Explosion TheoryUsing more than 30 state-of-the-art 3D core-collapse simulations to unprecedented late times, we have derived correlations between core-collapse supernova observables and progenitor core structures. This is the largest collection of 3D supernova models ever generated and allows one to witness and derive testable patterns that might otherwise be obscured when studying one or a few models in isolation. From this panoramic perspective, we see correlations between explosion energy, neutron star gravitational birth masses, the yields of the chemical elements, and pulsar kicks and theoretically important correlations with the compactness parameter of progenitor structure. We find a correlation between explosion energy and progenitor mantle binding energy, suggesting that such explosions are in part self-regulating. We see systematic correlations between progenitor structures and their gravitational-wave and neutrino signals. We find multiple channels for black hole formation and a spectrum of black hole observables. We also find a testable correlation between explosion energy and measures of explosion asymmetry, such as the ejecta mass dipole, and we see a path forward to explain pulsar and magnetar magnetic fields. However, while I contend the core-collapse supernova problem is now qualitatively solved, there is much yet to do in supernova theory before it can robustly and quantitatively explain the variety of supernova observations.
Josh Winn Lecar Lecture: The Transiting Exoplanet Survey Satellite CfA Colloquium 2024-10-02 | Lecar Lecture: The Transiting Exoplanet Survey SatelliteA transiting planet invites us to measure its size, mass, atmospheric composition, and other characteristics. However, the invitation can only be accepted if the planet's host star is bright enough for precise follow-up observations. Finding the brightest and most observationally favorable systems is the ongoing mission of NASA's Transiting Exoplanet Survey Satellite (TESS). Conceived in 2006 here in Cambridge as a partnership between MIT and the Center for Astrophysics, TESS was ultimately launched in 2018 as a NASA Explorer Mission. TESS uses four 10-cm telescopes to repeatedly image a 24 x 96 degree field of view, which is switched every 27 days to progressively cover the entire sky. So far, TESS data have resulted in 7000 planet candidates. Hundreds of planetary mass measurements have helped to distinguish between rocky "super-Earths" and lower-density "mini-Neptunes", while observations with the James Webb Space Telescope are starting to reveal the secrets of their atmospheres. More broadly, TESS probes the optical variability of a wide range of astronomical objects, including stars, asteroids, comets, supernovae, and active galactic nuclei. This presentation will review the history of TESS, some of the most interesting findings, and the ways you might use the data yourself.
Ralf Klessen The First Stars: Formation, Properties, and Impact CfA Colloquium 2024-09-25 | The First Stars: Formation, Properties, and ImpactThe first generation of stars, often called Population III (or Pop III), form from metal-free primordial gas at redshifts z ~ 30 and below. They dominate the cosmic star formation history until z ~ 20-15, at which point the formation of metal-enriched Pop II stars takes over. I review current theoretical models for the formation, properties and impact of Pop III stars, and discuss observational constraints. I argue that primordial gas is highly susceptible to fragmentation and Pop III stars form as members of small clusters with a logarithmically flat mass function. Feedback from massive Pop III stars plays a central role in regulating subsequent star formation, but major uncertainties remain regarding its immediate impact. Direct observations of Pop III stars in the early Universe remain extremely challenging, whereas stellar archeological surveys allow us to constrain both the low-mass and the high-mass ends of the Pop III mass distribution. Observations suggest that most massive Pop III stars end their lives as core-collapse supernovae rather than as pair-instability supernovae. I also focus on the formation of supermassive stars, which under very specific circumstances can get as massive as several 100.000 solar masses and become the seeds of supermassive black holes in the high-redshift universe.
CfA Seminar CfA Colloquium 2024-09-25 | Mojtaba Akhavan-Tafti Magnetic Switchbacks Contribute to Solar Wind Acceleration and HeatingMagnetic switchbacks are reversals (deflection angle θ_B greater than 90°) in the radial magnetic field B_r, accompanied by proton bulk flow v_p enhancement. The switchback generation mechanism(s) is still debated, though switchback evolution is linked to coronal heating. In this study, we provide an exhaustive investigation of magnetic fluctuations in the first 14 Parker Solar Probe (PSP) encounters. Our results show (1) enhanced magnetic fluctuations (θ_B less than or equal to 90°), and (2) clear absence of B_r reversals θ_B greater than 90° in sub-Alfvénic solar corona. It is concluded that switchbacks are either generated locally in super-Alfvénic solar wind (in situ) or that a subpopulation of magnetic fluctuations generated in sub-Alfvénic solar corona (ex situ) evolves into switchbacks once in super-Alfvénic solar wind flow. In other words, in situ mechanisms are necessary for switchback formation. A complimentary study further examines the evolution of a bundle of switchbacks, referred to as a switchback patch, during a PSP-Solar Orbiter radial alignment. Switchback patches are found to evolve into microstreams, defined as bundles of magnetic flux tubes with enhanced v_p, relative to the ambient solar wind. Our studies further confirm increasing evidence that the evolution of magnetic switchbacks contribute to solar wind acceleration and heating.Casey Brinkman Rocky Planet Compositions Tend to be Earth-like and Consistent with Host Star AbundancesSuper-Earth sized exoplanets, while non-existent in the solar system, are plentiful throughout the galaxy. However, these planets showed such a diversity in densities that some appear to be made entirely of iron, while others appear to have a negligible iron core or host envelopes of high mean molecular weight species. To test this diversity, we conducted a campaign using 124 high precision RVs from Keck/KPF and 154 from Gemini/MAROON-X to present the best masses yet for 6 rocky planets, along with confirmation of the planet TOI-1011 b . All updated planet masses (except TOI-561 b) suggest compositions closer to that of the Earth than previously determined, showing fewer iron-enriched “super-Mercuries.” TOI-561 b, on the other hand, suggests some super-Earth sized planets, even those on ultra-short period orbits, might indeed host gaseous envelopes and cannot be assumed to be purely rocky. We then compare the ratio of iron to rock-building species in the planets to the iron and magnesium abundance ratios in their host stars. These updated planet compositions do not suggest a steep relationship between planet and host star compositions, contradictory to previous results, and suggest a relationship much closer to 1-to-1.
Sara Issaoun pH Lecture: Toward a Precision Laboratory for Black Hole Studies CfA Colloquium 2024-09-18 | Sara Issaoun (Center for Astrophysics) - the pH Lecture"Toward a Precision Laboratory for Black Hole Studies"Using a network of eight radio telescopes at six geographic locations spanning the Earth, the Event Horizon Telescope (EHT) produced the first images of supermassive black holes in 2019 and 2022, launching the field of direct horizon-scale study of the spacetime and environments around black holes via direct imaging. The expansion of the capabilities of the EHT, through a denser network and an extension to space, will enable studies of black holes on unprecedented scales. In the next decade, the EHT will have the capability to make detailed high-dynamic range millimeter and sub-millimeter polarimetric movies of M87, Sagittarius A*, and other black hole targets – tracing the dynamical processes underlying black hole accretion and jet launching while zeroing in on stationary horizon-scale features that reveal the imprint of black hole spin. In this talk, I will discuss the journey to imaging black holes and my role in the various efforts to bring us to the era of high-definition black hole cinema.We understand that the refreshments will return this Tuesday to the excellent fare we have enjoyed over the years. Please arrive early so that we may begin promptly.
Damiano Caprioli The Non-thermal Universe CfA Colloquium 2024-09-11 | The Non-thermal UniverseNon-thermal particles are ubiquitous in the Universe: we can detect them at Earth as cosmic rays, probe them in-situ with spacecraft in the heliosphere, and observe their emission from galactic and extra-galactic objects over a vast range of frequencies spanning from radio to gamma-rays. I present some paradigmatic examples of how ab-initio plasma simulations can be used to further our understanding of particle acceleration and transport, and eventually the non-thermal phenomenology of several astrophysical objects. Moreover, I illustrate how cosmic rays and magnetic fields can play a crucial role in the interstellar medium and hence in galactic dynamics and evolution.
Gary Zank Adriaan van Ballegooijen Lecture CfA Colloquium 2024-09-11 | Adriaan van Ballegooijen Lecture: The heating of the solar corona and acceleration of the solar wind: Insights, theory, and modelingThe problem is easily stated and yet has endured for longer than the space age: the surface temperature of the Sun is a mere 6,500 degrees Kelvin yet the temperature of the solar corona exceeds 1 million degrees, hot enough to create a supersonically expanding wind that fills interplanetary space. What heats the solar corona? Fifty years after the discovery of the solar wind and the beginning of the space age, this remains the most outstanding unanswered question in space physics. This is also one of the questions that Aad van Ballegooijen focused on for much of his career, obtaining a series of seminal results that illuminated our understanding of the problem and laying much of the groundwork for solving this challenging question. NASA’s Parker Solar Probe and ESA’s Solar Orbiter spacecraft are making in situ and remote measurements of the young solar wind plasma and magnetic fields in attempting to answer the question of coronal heating and solar wind acceleration. An emerging consensus is that the solar corona is heated via the transport and dissipation of low-frequency magnetohydrodynamic turbulence. This presentation will review relevant Parker Solar Probe and Solar Orbiter observations in the context of current solar turbulence theory and modeling to show that we may be arriving at a solution to the 50-year question of the origin of the supersonic solar wind.
Charlie Conroy Assembling our Galaxy: The view from the MMT CfA Colloquium 2024-09-11 | I will provide an overview of and highlights from the recently completed H3 Stellar Spectroscopic Survey of our Galaxy. The survey has collected high resolution spectra of greater than 300,000 stars over a period of seven years using Hectochelle on the MMT. These spectra, when combined with Gaia astrometry, have provided an unprecedented view of the kinematics, chemistry, and ages of stars in our Galaxy. I will review how these data uncovered the formation and hierarchical assembly of the Galaxy from its birth to the present epoch.
Ligia Bouton Artist Talk July 24th 2024 CfA Colloquium 2024-07-25 | Ligia Bouton on her artwork, "25 Stars: A Temporary Monument for Henrietta Swan Leavitt"
CfA Colloquium Ivano Dal Prete (Yale University) CfA Colloquium 2024-07-17 | Ivano Dal Prete (Yale University)"The Moon Deluge and other Otherworldly Catastrophes. Astronomy and Earth History at the Turn of the Eighteenth Century"The idea that other planetary bodies can enlighten the geological history of the Earth is hardly a recent concept. Since antiquity, the action of the Sun, the Moon and other celestial objects was regarded as the root cause of climatic and geological change. The invention of the telescope (re)ignited speculation on extra-terrestrial life and its implications for the origins of humankind. At the turn of the eighteenth century, planetary astronomy became heavily embroiled in controversies on the physical reality of the Genesis Flood. Astronomers, philosophers, and theologians looked at the rugged surface of the Moon in search of evidence for other Deluges sent to punish other sinful humanities. Close encounters with comets seemed plausible agents of the biblical catastrophe and of the final Armageddon. Conversely, the enigmatic markings of Mars and Venus suggested sudden geological revolutions that could explain the origin of marine fossils without any need for a global inundation. The validation and interpretation of astronomical data reflected the cultural assumptions and societal norms of the time, raising questions that are now more relevant than ever on what constitutes a scientific “fact” and how it comes to be accepted – or rejected – across the broader society.
Nadja Drabon (Harvard University) CfA Colloquium 2024-05-13 | Better AudioNadja Drabon (Harvard University)"The Effect of the Giant 3.26 Gyr Meteorite impact on the Earth’s Early Surface Environment and Life"Large meteorite impacts strongly affected the habitability of the early Earth. The rocks of the Archean Eon record at least 16 major impact events with bolides larger than 10 km in diameter. These impacts likely had severe consequences for the surface conditions of early Earth. I will present on the analysis of sedimentary rocks across the 3.26 Ga S2 impact event (37-58 km bolide) to evaluate its environmental effects and consequences for early life. The results reveal that the impact caused a giant tsunami, evaporation of the uppermost layer of the ocean, and an increase in iron by mixing Fe 2+ -rich deep with Fe 2+ -poor shallow waters. Although meteorite impacts are usually seen as destructive and the S2 impact certainly had disastrous short-term consequences, it may have had some medium-term benefits for the early biosphere. The mixing of Fe 2+ to the upper water column potentially provided electron donors to the photic zone. In addition, the post-impact hothouse environment may have led to increased erosion and weathering, injecting nutrients like phosphorus into the oceans. Overall, meteorite impacts may have had transient benefits for early life on Earth.
Matthew Payne (Minor Planet Center) Planetary Defense and the Minor Planet Center CfA Colloquium 2024-04-17 | Matthew Payne (Minor Planet Center)"Planetary Defense and the Minor Planet Center "NASA's Planetary Defense Coordination Office (PDCO) coordinates and funds a variety of activities related to Near Earth Objects, including detection, characterization, impact assessment, mitigation strategies and international collaboration. I'll highlight a number of these activities, including the lessons learned from the Double Asteroid Redirection Test (DART) mission, as well as the results expected from the forthcoming NEO Surveyor mission. I'll then discuss the Minor Planet Center's (MPC) role in these planetary defense efforts, in which the MPC acts as the central hub for the collection, verification, and dissemination of data on minor planets, comets, and outer irregular natural satellites, and functions as the backbone of the NEO network monitoring, ensuring that observations are accurately processed and shared, and enabling timely decisions in the event of a potential impact threat.
New Results from the Event Horizon Telescope CfA Colloquium 2024-03-28 | The EHT will be releasing a major new result this Wednesday (3/27). This is a project led by Sara Issaoun and Angelo Ricarte here at the CfA, and they have organized a special colloquium with a series of talks from key contributors to present the results (including Freek Roelofs at the CfA, and two visiting scientists, Avery Broderick and Michi Baubock).
Ashley Villar (Center for Astrophysics) Data-driven Methods to Understand the Dynamic Universe CfA Colloquium 2024-03-27 | Ashley Villar (Center for Astrophysics)"Data-driven Methods to Understand the Dynamic Universe"Wide-field astronomical surveys have enabled the discovery of thousands of transient phenomena annually. In parallel, the development of machine learning techniques has revolutionized how we analyze astronomical data. Variable phenomena–supernovae, active galactic nuclei, pulsating stars, etc.–are uniquely challenging due to their intrinsic and observed diversity. In this colloquium, I will explore the development of physics-informed machine learning, particularly in the context of time-domain astrophysics. I will highlight advances in realtime modeling of time-series and its application to the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time. I will end with reflections on recent developments in generative artificial intelligence and how these may impact future survey science.
Dillon Brout Cosmological Results from the Full 5 Years of the Dark Energy Survey Supernova Program CfA Colloquium 2024-03-20 | Dillon Brout (Boston University)"Cosmological Results from the Full 5 Years of the Dark Energy Survey Supernova Program"Type Ia Supernovae (SN) remain a central pillar of the Standard Model of Cosmology - Lambda Cold Dark Matter (LCDM). I will detail leaps of progress in the last 5 years of supernova cosmology culminating in the recent Dark Energy Survey (DES) analysis of ~1700 photometrically classified supernovae collected over 5 years that rivals the spectroscopically confirmed Pantheon+ compilation of more than 30 years of supernovae. The DES dataset is the largest dataset ever compiled from a single telescope and places strong constraints on dark matter and dark energy. I will detail the robust systematic uncertainties that have built confidence in these measurements and that paves the path forward for future surveys.
Jason Wang New Frontiers in Exoplanet Imaging and Pathways to Habitable Worlds CfA Colloquium 2024-03-11 | Jason Wang (Northwestern University)"New Frontiers in Exoplanet Imaging and Pathways to Habitable Worlds"By spatially resolving faint planets from their bright host stars, we can directly characterize them as individual worlds. Exoplanet imaging is a technology-driven field, and I will discuss three new novel instruments that allow us to detect and characterize imaged Jovian exoplanets and whose technology, if placed on the next generation of observatories, has the potential for us to study habitable worlds. The Keck Planet Imager and Characterizer (KPIC) combines high-contrast imaging and high-resolution spectroscopy techniques together for the first time and allows us to spectrally resolve molecular absorption lines in the atmospheres of directly imaged planets. Long-baseline interferometry with VLTI/GRAVITY gives us the spatial resolution of a 140-meter telescope, enabling the positions of exoplanets to be measured to within 50 microarcseconds, the circumplanetary environment to be resolved to sub-au scales, and the first direct detection of a radial-velocity discovered exoplanet. Both techniques also unlock the ability to study giant planets at 1-10 au like our own Jupiter. Moving to space, the Roman Space Telescope Coronagraph Instrument will demonstrate high-order wavefront control and potentially image a planet in reflected light for the first time, allowing us to measure planetary albedo. I will highlight recent science results from these instruments, summarize lessons learned in pioneering these techniques, and discuss their prospects for imaging habitable worlds on the next generation of observatories.
Dan Milisavljevic (Purdue University) Supernovae: Laboratories of Extreme Astrophysics CfA Colloquium 2024-03-06 | Dan Milisavljevic (Purdue University)"Supernovae: Laboratories of Extreme Astrophysics"Core-collapse supernovae are among the most powerful explosions in the universe. They shape and enrich their host galaxies; produce a variety of exotic objects including neutron stars, black holes, and some gamma-ray bursts; are a major site of nucleosynthesis; and serve as ideal laboratories of multimessenger astrophysics. I will review how radio-through-X-ray investigations of transients are revolutionizing our understanding of stellar death and its myriad impacts. Particular attention will be placed on how observations are characterizing the terminal and often dramatic evolutionary phases massive stars pass though when approaching core collapse, and how 3D reconstructions of supernova remnants can directly address uncertainties in supernova progenitor systems and explosion mechanisms. The special role of observations made possible by the James Webb Space Telescope will be highlighted. Finally, I will conclude by describing how new synergy between electromagnetic, neutrino, and gravitational wave facilities can enable transformative progress towards finally solving the enigma of core collapse by accurately interpreting the multi-messenger signals from the next Galactic supernova -- a once-in-a-generation event that will be detected by a network of neutrino detectors called the Supernova Early Warning System.
Aki Roberge (NASA Goddard Space Flight Center) Towards the Habitable Worlds Observatory CfA Colloquium 2024-02-28 | Aki Roberge (NASA Goddard Space Flight Center)"Towards the Habitable Worlds Observatory"Humans have long wondered if there were worlds around other stars – and life on those worlds. Over the last two decades, astronomers have found that the answer to the first question is a resounding YES. Those accomplishments have put us in a position to possibly answer the second question. The 2020 Astrophysics Decadal Survey (Astro2020) has laid out a path to the first telescope that can find out if habitable exoplanets are common or rare and search them for signs of global biospheres, while performing a wide range of transformative astrophysics studies.NASA has dubbed that telescope the Habitable Worlds Observatory (HWO). In this talk, I’ll cover Astro2020’s recommendations and expectations for HWO, as well as the previous mission concept studies that fed into it (LUVOIR and HabEx). I’ll then move on to NASA’s current plans for maturation of the HWO concept, highlighting key challenges and activities. This multi-faceted journey will require enthusiastic collaboration between a wide range of disciplines, interests, and stakeholders. Continuing out into future decades, the path may lead to a new generation of Great Observatories in space and new perspectives on the universe around us.
Jason Wang New Frontiers in Exoplanet Imaging and Pathways to Habitable Worlds CfA Colloquium 2024-02-21 | Jason Wang (Northwestern University)"New Frontiers in Exoplanet Imaging and Pathways to Habitable Worlds"By spatially resolving faint planets from their bright host stars, we can directly characterize them as individual worlds. Exoplanet imaging is a technology-driven field, and I will discuss three new novel instruments that allow us to detect and characterize imaged Jovian exoplanets and whose technology, if placed on the next generation of observatories, has the potential for us to study habitable worlds. The Keck Planet Imager and Characterizer (KPIC) combines high-contrast imaging and high-resolution spectroscopy techniques together for the first time and allows us to spectrally resolve molecular absorption lines in the atmospheres of directly imaged planets. Long-baseline interferometry with VLTI/GRAVITY gives us the spatial resolution of a 140-meter telescope, enabling the positions of exoplanets to be measured to within 50 microarcseconds, the circumplanetary environment to be resolved to sub-au scales, and the first direct detection of a radial-velocity discovered exoplanet. Both techniques also unlock the ability to study giant planets at 1-10 au like our own Jupiter. Moving to space, the Roman Space Telescope Coronagraph Instrument will demonstrate high-order wavefront control and potentially image a planet in reflected light for the first time, allowing us to measure planetary albedo. I will highlight recent science results from these instruments, summarize lessons learned in pioneering these techniques, and discuss their prospects for imaging habitable worlds on the next generation of observatories.
Prof. Jun Ye (JILA & NIST) Quantum degenerate gas of polar molecules CfA Colloquium 2024-02-07 | Prof. Jun Ye (JILA & NIST)"Quantum degenerate gas of polar molecules"In his 2001 seminal paper on cold chemistry, Prof. Dalgarno predicted a considerable rate for chemical reaction near zero temperature owing to “tunneling through the repulsive barrier”. His vision inspired a vibrant development of the field of ultracold molecules and was fully validated when a molecular gas was brought into the quantum regime, where ultracold collisions and chemical reactions were shown to be governed by quantum statistics and long-range interactions.Quantum degerate gas of molecules sets the stage to explore novel dynamics. External electric fields are used to tune elastic interactions, suppress reactive losses, produce sharp collision resonances, and control evaporative cooling. Confining molecules in optical traps with various spatial geometries allows realization of stereo chemistry and construction of tunable many-body spins for quantum magnetism. Hamiltonian engineering is paving the way for production of entangled molecules that will benefit precision measurement.
Joanna Drazkowska The Emerging Theory of Planet Formation CfA Colloquium 2024-01-31 | Joanna Drazkowska (Max Planck Institute for Solar System Research)"The Emerging Theory of Planet Formation"The classical theory of planet formation originated when our knowledge about planets was limited to the Solar System alone. The numerous discoveries of exoplanet systems have compelled a revision of this theory, aided by cutting-edge observations of circumstellar disks and precise laboratory studies of Solar System materials. Nonetheless, the formation of planets remains one of the major unsolved problems in modern astrophysics. In this talk, I will outline the emerging paradigm in which centimeter-sized dust aggregates, colloquially known as pebbles, take center stage. I will explore the challenges in the growth process from tiny dust grains to pebbles, identifying key barriers that hinder this progression. Due to these barriers, the formation of planetesimals, the first gravitationally-bound building blocks preceding today's asteroids and comets, remains particularly enigmatic. Notably, the emergence of planetesimals is now believed to occur only in specific locations within the circumstellar disk, such as the water snow line. Therefore, these early stages of planet formation may significantly influence the final architectures of planetary systems.
Jessica Dempsey(ASTRON) Harnessing the Opportunities in the Approaching Radio Astronomy Renaissance CfA Colloquium 2024-01-17 | Jessica Dempsey (ASTRON)"Harnessing the Opportunities in the Approaching Radio Astronomy Renaissance"Radio astronomy is about to step into a new era of technical and scientific capability. ASTRON leads the expansion of LOFAR, while SKA enters construction of the largest radio observatory ever built. On the horizon, to complement and compete, are the ngVLA and DSA-2000. ASTRON, as the Netherlands centre for radio astronomy, looks now to its role in this renaissance, and in its opportunities with our LOFAR and SKA partners. ASTRON is developing a science data centre to lead the world in providing the broadest accessibility to science-ready data products in the radio regime, committed to lowering the barrier of access to the radio universe for the widest community of astronomers possible, in advance of hosting the upcoming SKA regional centre. The coming renaissance is not without challenge – particularly in facing and overcoming the daunting data collection, processing and storage bottlenecks and to develop green solutions for our expanding environmental impacts. ASTRON is developing its long-look strategic plan around these goals with our national and international community, focusing on ensuring in this decade of world-spanning facilities, we maintain agency and opportunity for our researchers to lead impactful science and technology developments.
CfA Colloquium 1:30pm Brian Metzger CfA Colloquium 2023-10-25 | Brian Metzger (Columbia University)"Strange Occurrences in Galactic Nuclei"Galactic nuclei can host a number of transient phenomena involving the violent interactions of stars with the central supermassive black hole (SMBH) or its accretion disk. Stars placed on parabolic orbits which pass too close to the SMBH give rise to tidal disruption events (TDE). I will highlight several puzzles related to the appearance of TDEs flares, particularly their unexpectedly modest effective temperatures (larger than expected photosphere radii) and the recent discovery of late-time radio flares delayed many months or years after the optical light curve peak. Motivated by these issues, I will describe a new model in which the disrupted stellar debris forms a quasi-spherical pressure-supported envelope around the SMBH, which undergoes cooling-driven (Kelvin-Helmholtz) contraction, only gradually forming the inner accretion disk responsible for X-ray and radio jetted emission. In contrast to TDEs, stars which migrate into the galactic center through gravitational wave emission on low-eccentricity orbits ("extreme mass-ratio inspirals"; EMRIs) can survive in the immediate vicinity of SMBH for considerably longer, at least until a gaseous disk is produced (e.g., via a TDE). I will show that the recently discovered sources of X-ray "quasi-periodic eruptions" (QPEs) arise naturally from repeated collisions of an orbiting stellar EMRI with a SMBH disk. If this explanation is correct, QPEs offer a new probe of the EMRI population in galactic nuclei; the structure of radiation-dominated accretion disks; and strong-gravity effects such as apsidal/nodal orbital precession.
CfA Colloquium 1:30pm Iouli Gordon CfA Colloquium 2023-10-18 | Iouli Gordon (CfA)"The HITRAN and HITEMP Molecular Spectroscopic Databases: Empowering Remote Sensing Missions"The HITRAN molecular spectroscopic database, traditionally used as an international reference standard for terrestrial atmosphere research, has evolved significantly over its five-decade history. Recent advances in the quality of spectra obtained from on-ground and space-based spectrometers have established the incredible diversity of planetary and exoplanetary atmospheres, not just in thermodynamic conditions but also in composition. To meet the demands of this evolving field, HITRAN has expanded its scope through 1) the inclusion of molecules relevant to non-terrestrial atmospheres; 2) updating and expanding the high-temperature counterpart of the database, HITEMP; 3) adding collision-induced absorption data; and 4) adding pressure-broadening parameters due to ambient gases dominating planetary atmospheres (e.g., CO2, H2 and He). The philosophy behind database development can be summarized as a PACT: Practicality, Accuracy, Completeness, Traceability. Examples of applying this philosophy will be given, highlighting, in particular, a robust process for curation and validation of the parameters, for instance, against high-quality laboratory spectra or atmospheric measurements.This presentation will explore the current state of these databases and associated tools and provide insight into their future developments.
Julien de Wit Robustly Characterizing Exoplanets in a New Era of High-Precision Transit Measurements CfA Colloquium 2023-10-11 | Robustly Characterizing Exoplanets in a New Era of High-Precision Transit MeasurementsOctober 10, 20231:30 PMAbstract: With a new-generation of great observatories coming online this decade, unprecedented insights into exoplanets are becoming within reach. JWST for example can enable the study of atmospheres around terrestrial exoplanets and reveal tri-dimensional structures in the atmospheres of their larger counterparts. Yet, robustly leveraging new data to reach such achievements will require extra care as the models currently used may not be up to par.During this presentation, I will introduce work done by MIT’s Disruptive Planets group and collaborators towards supporting the robust in-depth characterization of exoplanets. I will specifically discuss how not accounting for the true shape of a planet can lead to a misinterpretation of its interior properties as well as atmospheric structure; how the current state of our understanding of light-matter interactions can similarly affect our interpretation of planetary spectra and thus inferences regarding their atmospheric properties; and how the current state of emission spectrum models for stars may even prevent from disentangling between the contribution of a planet and its host star, to start with. I will then present possible ways to address these challenges and end with a step-by-step roadmap to the robust characterization of temperate terrestrial planets with JWST, which includes habitability assessment.
Blake Sherwin: Do we understand cosmic structure growth? CfA Colloquium 2023-10-04 | Blake Sherwin (University of Cambridge)"Do we understand cosmic structure growth? Insights from new CMB lensing measurements with the Atacama Cosmology Telescope"
Morgan MacLeod pH Lecture: Breaking Waves on a Stellar Shore CfA Colloquium 2023-09-27 | Morgan MacLeod pH Lecture: Breaking Waves on a Stellar Shore
Jenna Samra High-Altitude Instrumentation for Infrared Observations of the Solar Corona CfA Colloquium 2023-09-20 | Jenna Samra High-Altitude Instrumentation for Infrared Observations of the Solar Corona
Sandro Tacchella First Insights from JWST: Star Formation in Cosmic-Dawn Galaxies CfA Colloquium 2023-09-13 | First Insights from JWST: Star Formation in Cosmic-Dawn GalaxiesSeptember 12, 20231:30 PM - 2:30 PMAbstract: After successful deployment and commissioning, JWST has now been delivering data for over a year. I will give an overview of the first-year surprises and discoveries, zooming in on some of the earliest galaxies and presenting new results on the spatially resolved growth histories of high-redshift galaxies. Specifically, I will discuss the structural and stellar population properties of the galaxies at the redshift frontier, with redshifts z 10. I will then connect the mode of star formation with the early enrichment of galaxies: for galaxies where we have constraints on the gas-phase metallicity (at redshift of z=8), I will show how star-bursting galaxies can have different gas-phase metallicities due to internal and external mechanisms that drive the starburst. Finally, I will focus on the structural evolution of galaxies, presenting how dense stellar cores form within galaxies at z 7. I will wrap up by highlighting what JWST will be able to deliver regarding high-redshift galaxy evolution in the upcoming years.Speaker InformationSandro TacchellaUniversity of Cambridge
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A Sky Full of Satellites: The changing orbital population and the impact of megaconstellations CfA Colloquium 2023-05-24 | aired 1/31/23
Exoplanets with JWST: How one telescope revolutionized a field in about 100 Days CfA Colloquium 2023-05-24 | ...
Searching for Black Holes From the Nearby to the Faraway Universe CfA Colloquium 2023-04-12 | I will provide an overview of our quest to understand, with theory and observations, undetected populations of black holes, proceeding from the nearby to the faraway Universe. First, I will unveil a new extensive, multiwavelength observational campaign likely leading to the discovery of the second closest supermassive black hole, located in the Milky Way satellite Leo I. I will then describe some orbital and radiative properties of intermediate-mass black holes potentially wandering in local galaxies, including the Milky Way. Moving higher in the redshift ladder, I will detail the detection of the farthest lensed quasar to date and theoretical arguments as to why we are missing a significant fraction of this population. Still in the reionization epoch, I will delineate the discovery of two candidate galaxies at redshift z greater than 10 and the possibility that they host supermassive black holes. I will then conclude with the observational properties of the same sources that have started the reionization at z ~ 30: the first population of stars and black holes, and how we may soon be able to detect them directly.
How Supermassive Black Holes Ignite the Intergalactic Medium CfA Colloquium 2023-04-05 | The Lyman-α forest is a key diagnostic for the state of diffuse baryons in the intergalactic medium (IGM) and for fundamental cosmological parameters. At high redshift (i.e., z ≥ 2) the Lyman-α forest is observed in optical wavelengths from ground-based observatories and has been used to constrain small-scale cosmic structure, the dark matter distribution, the IGM gas temperature, and the evolution of the ultraviolet ionizing background (UVB) radiation. However, the low redshift (z~0.1) Lyman-α forest, observed from space-based UV instruments such as HST COS, has challenged the most advanced cosmological simulations. In this talk, I will show how active black hole (AGN) feedback can be at least as important (or more!) as the UVB for setting the amount and distribution of neutral gas in the low redshift IGM. The AGN feedback signatures appear in the neutral gas statistics beginning around z~1, thus possibly affecting 21-cm intensity mapping programs that target this redshift range (e.g., HIRAX). These findings herald a significant paradigm shift for cosmological simulations and observations that target the low redshift IGM and suggest that cosmological simulations should develop AGN feedback models with both galaxies and the IGM in mind.
The Emergence of Galactic Structure in the JWST Era CfA Colloquium 2023-03-29 | The launch and commissioning of the James Webb Space Telescope is ushering in a new era in our understanding of our cosmic origins. Galaxies are a fundamental building block of the universe, yet how they formed has remained enigmatic owing to our inability to observe them at early cosmic times. In just the first eight months of data JWST is already revolutionizing our understanding of the earlyuniverse by allowing us to detect and resolve early galaxies at infrared wavelengths. In this talk, I will discuss some of the results that have come out of our work with JWST and their impact on our understanding of the formation and evolution of galaxies. This includes the discovery of candidate galaxies so old and massive they should not exist, the surprising shapes of HST-dark galaxies, and a new method for measuring kinematics that has revealed a monstrous spinning disk 1 billion years after the big bang. The first spatially-resolved infrared look at distant galaxies has revealed that our previous understanding of the emergence of galactic structure was faulty and requires a next-generation set of tools, which we are building. I’ll conclude with a discussion of where the field is moving and the rich discovery space in this new era of extragalactic astrophysics.
