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Staff Research
2017 Spring Series

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:30 p.m. preceded by tea at 3:15 p.m.

Please direct questions or comments to the colloquium committee. The 2016-17 committee members are Brad Whitmore (chair), Gabe Brammer, Andy Fruchter (ex officio), Olivia Jones and Nora Luetzgendorf.

STScI presents live and archived webcasting of talks and Colloquium Series.

Date Speaker/Title
Feb. 01 (CoolSci Talk Series)
Feb. 08 (No Colloquium)
Feb. 15 Amy Reines (National Optical Astronomy Observatory)
Title: The Origin of Supermassive Black Holes
Abstract: The origin of supermassive black holes remains a major outstanding issue in modern astrophysics. These monster black holes reside in the nuclei of essentially every massive galaxy and power the most luminous quasars at the edge of the observable Universe. However, directly observing the first “seed” black holes in the early Universe - that can eventually grow to upwards of a billion solar masses - is not feasible with current telescopes. Present-day dwarf galaxies, on the other hand, are within observational reach and offer another avenue to learn about black hole seeds since low-mass galaxies can host relatively pristine black holes. In this talk, I will highlight some of my recent achievements in this field that have taken us from a few rare examples to large systematically-assembled samples of dwarf galaxies hosting nuclear black holes. I will also discuss how my work has implications for directly detecting black hole activity in the first galaxies at high redshift.
Host: Nora Luetzgendorf
Feb. 22 Jessica Lu (University of California Berkeley)
Title: Finding Black Holes with Astrometric Microlensing
Abstract: TBS
Host: Andrea Bellini
Mar. 01 Renée Hlozek (University of Toronto)
Title: Constraining Ultra-light Axions with CMB data: Shining Light on the Lightest Particle Dark Matter Candidates
Abstract: CMB cosmology is currently undergoing a data-rich epoch, with measurements on small scales from experiments like the Atacama Cosmology Telescope (ACT) and its polarisation instrument, ACTPol, adding to measurements on larger scales by Planck, WMAP and most recently BICEP. I will contextualise the measurements and present constraints on cosmological models of interest to small-scale experiments; while noting that foregrounds that complicate our measurements of the primordial microwave sky. I'll present recent ACTPol results and highlight the next generation of the experiments in the Simons Observatory and the Fourth Stage CMB experiment (CMB S4): ensuring CMB cosmology has a rich future to look forward to on the ground!
I'll also concentrate on how we can use the CMB to constrain the lightest potential dark matter particles. I'll pay particular attention to constraints on models of ultra-light axions (ULAs). ULAs are a type of dark matter well motivated by particle physics, that impact our cosmological measurements by suppressing structure and affecting the CMB. I'll highlight previous work which constrained ULAs with mass in the range 10-^{32} eV→10^{-26} eV, current limits are that they can compose a fraction <0.01 of the cosmological critical density of the universe. CMB-S4 should be ~10 times more sensitive to the ULA energy-density than Planck data alone, across a wide range of ULA masses 10-32 < ma < 10-23 eV, and will probe axion decay constants of fa≈1016 GeV, at the grand unified scale. It should also improve the CMB lower bound on the ULA mass from ~10-25 eV to 10-23 eV, nearing the mass range probed by dwarf galaxy abundances and dark-matter halo density profiles. These improvements will allow for a multi-σ detection of percent-level departures from CDM over a wide range of masses.
Host: Arfon Smith
Mar. 08 Mike Brown (California Institute of Technology)
Title: Planet Nine from Outer Space
Abstract: The recent suggestion of evidence for a massive ninth planet in the outer solar system has set off a worldwide search to find this latest member of our planetary family. I will discuss the evidence for the planet and show how we are working to constrain the mass and orbital parameters of the body. I will also point out some of the unexpected features in the solar system that ninth planet explains, including obliquity of our sun. Finally, I will show the latest results from the search for Planet Nine.
Host: Marc Rafelski
Mar. 15 (CANCELED)
Mar. 22 (CANCELED)
Mar. 29 Rob Kennicutt (University of Cambridge)
Title: From Gas to Stars
Abstract: It is now clear that the conversion of interstellar gas to stars, together with the subsequent feedback from massive star formation on the ISM are fundamental agents in the formation, evolution, and shaping of galaxies. Thanks to a wealth of recent observations from the ground and space our empiriral characterization of these processes is being revolutionized, yet our understanding of the underlying physical processes which trigger and regulate large-scale star formation remains embryonic. This talk will review the many advances made over the past decade in understanding the coupling of star formation to the interstellar medium, and highlight the key challenges which remain.
Host: Margaret Meixner
Apr. 05 (No Colloquium)
Apr. 12 Armin Rest (STScI)
Title: Taking the Measure of the Universe with Stellar Explosions
Abstract: Type Ia supernovae (SNe Ia) are superb distance indicators and are used to map the expansion history of the Universe. Two decades ago, astronomers used observations of SNe Ia to find that the Universe's expansion is currently accelerating. Since this initial discovery, we have used SNe Ia to constrain the nature of "dark energy," which drives this accelerated expansion. To improve our dark energy constraints beyond our current basic understanding, we must design new and better SN surveys as well as improve our understanding of the physics of the SN explosion itself. I will show how high-cadence Kepler telescope light curves have provided us with crucial insight into the progenitor channels and physics of SN explosions. With light echoes of historic SNe, we can investigate the cause (the explosion/eruption) and the effect (the remnant) of the same astronomical event, even allowing us to look at the same event from different directions. I will also present the Foundation Supernova survey, a new high-fidelity, low-redshift (z < 0.1) survey I started in 2015 that will replace the current heterogenous low-redshift sample and reduce the (currently) largest uncertainties for SN cosmology. I will discuss the next major leap in SN cosmology, pushing to high-redshift and NIR with JWST and WFIRST. With the combination of the Foundation survey, the next generation of space-based observatories, and new physical understanding, SNe Ia will remain a premier cosmological probe, continuing the legacy started decades earlier.
Host: Dave Soderblom
Apr. 19 Eliza Kempton (Grinnell College)
Title: Revealing the Atmospheres of Extrasolar Super-Earths
Abstract: Discoveries of extrasolar planets over the last two decades have reshaped our understanding of how planetary systems form. Super-Earths – planets intermediate in size/mass between Earth and Neptune – do not exist in our Solar System, and the discovery of such planets poses a challenge to theories of planetary formation and composition based on the Solar System paradigm. Through observations of the atmospheres of these planets, we can learn about their formation history, their climate, and in some cases their propensity to support life. This talk will focus on the modeling of super-Earth atmospheres as it relates to current and future observations. I will detail the current state of characterization efforts for super-Earth atmospheres, focusing on the challenges and successes in modeling and interpreting the early observations of these objects. I will conclude with a forward-looking view of super-Earth atmospheric studies over the next 5-10 years, in the era of JWST and 30-meter class ground-based telescopes.
Host: Nikole Lewis
Apr. 26 (Spring Symposium, No Colloquium)
May 03 Jan Cami (Western University)
Title: Space Buckyballs: The Hidden Life of Cosmic Fullerenes
Abstract: In recent years, the fullerene species C$_{60}$ (and to a lesser extent C$_{70}$) has been detected in a variety of astrophysical environments -- from the circumstellar carbon-rich surroundings of evolved stars to interstellar reflection nebulae and young stellar objects. Understanding how these species form, evolve and respond to their environment yields important insights into astrochemistry and the characteristics of large aromatics in space, thought to be the main reservoir of organic material in space. In this talk, I will present an overview of what we have learned about cosmic fullerenes from astronomical observations, theoretical calculations and recent laboratory experiments, and show how fullerenes have significantly changed our under- standing of interstellar chemistry. I will discuss the conditions that appear to be conducive to the formation and/or detection of fullerenes, and highlight some of the difficulties we still face in understanding the formation of fullerenes in planetary nebulae.
Host: Gail Zasowski
May 08 Rainier Weiss (Massachusetts Institute of Technology), Bahcall Lecture
Title: Observation of the Merger of Binary Black Holes: The Beginning of Gravitational Wave Astronomy
Abstract: Rainer Weiss on behalf of the LIGO Scientific Collaboration

After some history of gravitational waves will follow with a description of the waves and the technique for detecting them. Present and discuss the observations and end with a vision for the future of gravitational wave astronomy and astrophysics.
Host: TBD
May 10 Nikole Lewis (STScI)
Title: TRAPPIST-1: Beyond Imagination
Abstract: The past year has seen a bumper crop of Earth-sized exoplanets orbiting nearby stars, targets ripe for exoplanet characterization studies. The seven planets in the TRAPPIST-1 system, located 12 pc from our solar system, represent the largest number of Earth-sized planets orbiting a single star to date. Three of the TRAPPIST-1 planets reside in the traditional habitable zone of their host star. Perhaps more importantly, the TRAPPIST-1 planets all transit their host star as seen from Earth, which enables observational constraints on their bulk composition and atmospheric properties. Here I will discuss the discovery of the TRAPPIST-1 system and our current efforts to characterize these planets utilizing a wide range of observational, theoretical, and experimental tools. I will also discuss the potential for characterization of small (less than 1.6 Earth radii) temperate exoplanets, such those in the TRAPPIST-1 and the newly announced LHS 1140 systems, leveraging the combined power of Hubble and Webb. By spearheading continued observational, theoretical, and experimental efforts aimed at understanding the potential diversity of exoplanets, I am working to bring us one step closer to answering the question ‘Are We Alone?’.
Host: N/A
May 17 Adam Leroy (The Ohio State University)
Title: Observing the Physical State of the Cold Gas in Nearby Galaxies
Abstract: Thanks to new and revitalized facilities including ALMA, the IRAM telescopes, and the GBT, we are now able to access the physical conditions in the cold gas of other galaxies in ways previously reserved to studies of the Milky Way and Local Group galaxies. Using multi-line spectroscopy we are able to constrain the gas density distribution in each part of a galaxy, while using high resolution CO imaging we can measure the structure (density, turbulence, and self-gravity) of the interstellar medium on the scale of individual star-forming clouds across all types of galaxies. The ability to make such measurements over a large part of a star forming galaxy is new in the last few years, thanks to the IRAM programs EMPIRE and PAWS, the beginning of ALMA operations (and our PHANGS CO survey), and upgrades to the GBT. I will show how the amount of dense gas changes across the disk of galaxies, and illustrate a more nuanced role for gas density in star formation than commonly asserted. I will also show how the basic cloud-scale structure of the cold interstellar medium changes from galaxy-to-galaxy, reflecting the local environment, and I will show how these local structural conditions relate to gas density and star formation in the best studied nearby galaxies. Finally, I will highlight first results several new surveys with ALMA (as part of the PHANGS collaboration) that promise to give us a sharp new view of cold gas in nearby galaxies over the next years.
Host: Karl Gordon
May 24 Bob Abraham (University of Toronto)
Title: Early results from the Dragonfly Telephoto Array
Abstract: In this talk I will describe some early results from the Toronto/Yale/Harvard Dragonfly Telephoto Array (a.k.a. Dragonfly), a robotic imaging system optimized for the detection of extended ultra low surface brightness structures. Dragonfly is comprised of multiple (expensive!) commercial 400 mm f/2.8 telephoto lenses which have high-performance sub-wavelength nanostructure optical coatings designed to minimize scattered light and ghosting. This instrument is optimized to explore the night sky in a totally different parameter space from conventional ground-based telescopes, and in its chosen niche no other telescope can touch it: Dragonfly's wide-field low surface brightness imaging performance makes it capable of directly imaging low surface brightness structures (such as galactic streams, galaxy stellar halos and faint dwarf galaxies) about 10x fainter than is possible with conventional telescopes. In this talk I'll show some early results, mainly focusing on the properties of ultra-faint stellar halos, enormous stellar disks, and a new class of ghostlike galaxies that are as big as the Milky Way but have about 1/100 of its stellar mass. I will also report on our plans to upgrade the array order to enable a search for the Cosmic Web, a large­-scale network of dark matter filaments that is believed to connect galaxies to each other, and which is thought to be the largest coherent structure in the Universe.
Host: David Law
May 31 Jim Fuller (California Institute of Technology)
Title: Asteroseismology reveals strong magnetic fields in the cores of red giant stars
Abstract: Internal stellar magnetic fields are inaccessible to direct observations and little is known about their amplitude, geometry and evolution. I will discuss how strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields manifest themselves via depressed dipole stellar oscillation modes, which arises from a magnetic greenhouse effect that scatters and traps oscillation mode energy within the core of the star. The Kepler satellite has already observed hundreds of red giants with depressed dipole modes, which may be stars with strongly magnetized cores. Field strengths larger than roughly 10^5 G can produce the observed depression, and in one case a core field strength of 10^7 G is inferred. Strong core fields may be present in roughly 50% of stars above 1.5 solar masses, suggesting that long-lived convective core dynamo-generated fields are common within these stars. Strong core fields are nearly absent in stars less than 1.2 solar masses, indicating that Sun-like stars do not harbor strong fields within their cores.
Host: Steve Lubow