KICP Seminars & Colloquia, Current and Future
Today's Seminar
Upcoming Seminars

Seminar schedule for Current (Winter 2018) & Future Quarters
January 10, 2018
Wednesday colloquium
Erik P. Verlinde
University of Amsterdam
From Emergent Gravity to Dark Energy and Dark Matter   [Abstract | Video]
January 12, 2018
Friday noon seminar
Patricia Larsen
Argonne National Laboratory
Topics in weak lensing   [Abstract]
January 16, 2018
Astronomy Tuesday Seminar
Rachael Roettenbacher
Stockholm University
Surveying Spotted Stars with Photometric, Spectroscopic, and Interferometric Observations   [Abstract]
January 17, 2018
Astronomy Colloquium
Maggie Turnbull
SETI
WFIRST: Where Things Stand with the First Exoplanet Direct Imaging Flight Mission   [Abstract]
January 19, 2018
Friday noon seminar
Jessica M Turner
Fermi National Accelerator Laboratory
Discussion on old and new mechanisms of leptogenesis   [Abstract]
January 24, 2018
Wednesday colloquium
Laura Trouille
The Adler Planetarium and Northwestern University
Citizen Science Frontiers: Efficiency, Engagement, and Serendipitous Discovery with Human-Machine Systems   [Abstract | Video]
January 26, 2018
Friday noon seminar
Yao-Yuan Mao
University of Pittsburgh
Mass' not the only thing: Secondary effects in the galaxy-halo connection   [Abstract]
January 30, 2018
Astronomy Tuesday Seminar
Decker French
Carnegie Observatories
The deaths of galaxies and the growth of supermassive black holes: implications for galaxy evolution and tidal disruption events   [Abstract]
January 31, 2018
Astronomy Colloquium
Ellen Zweibel
University of Wisconsin-Madison
The Basis for Cosmic Ray Feedback   [Abstract]
February 2, 2018
Friday noon seminar
Daniel Jacobs
Arizona State University
High redshift 21cm intensity mapping Past, Present, and Future   [Abstract]
February 7, 2018
Wednesday colloquium
cancelled
Peter Adshead
University of Illinois at Urbana-Champaign
Gauge-field inflation and the origin of the matter-antimatter asymmetry   [Abstract]
February 8, 2018
Astronomy Special Seminar
Meredith MacGregor
Carnegie Department of Terrestrial Magnetism
Debris Disks as Probes of Planetary System Evolution   [Abstract]
February 9, 2018
Friday noon seminar
Francisco Villaescusa-Navarro
Center for Computational Astrophysics
The impact of massive neutrinos on cosmological observables   [Abstract]
February 13, 2018
Astronomy Tuesday Seminar
Maria Petropoulou
Princeton University
Relativistic Jets: Particle Accelerators of the Universe   [Abstract]
February 14, 2018
Astronomy Colloquium
Tim Heckman
Johns Hopkins University
Galactic Winds: Phenomenology, Physics, and Implication   [Abstract]
February 16, 2018
Friday noon seminar
Noah S Oblath
Pacific Northwest National Laboratory
Project 8: Towards a Direct Measurement of the Neutrino Mass with Tritium Beta Decays   [Abstract]
February 20, 2018
Astronomy Tuesday Seminar
Chanda Prescod-Weinstein
University of Washington
Making a Universe with Axions and Inflatons   [Abstract]
February 21, 2018
Wednesday colloquium
Abby Vieregg
The University of Chicago
Discovering the Highest Energy Neutrinos Using a Radio Phased Array   [Abstract]
February 28, 2018
Astronomy Colloquium
Enrico Ramirez-Ruiz
University of California, Santa Cruz
Heavy element synthesis in the Universe   [Abstract]
March 7, 2018
Astronomy Colloquium
Bekki Dawson
Pennsylvania State University
TBA
March 14, 2018
Wednesday colloquium
Katherine Freese
University of Michigan
Dark Matter in the Universe   [Abstract]
March 28, 2018
Wednesday colloquium
Luca Grandi
The University of Chicago
TBA   [Abstract]
April 4, 2018
Wednesday colloquium
Rush D Holt
AAAS
(KICP) Colloquium
April 11, 2018
Wednesday colloquium
Silvia Galli
IAP
Cosmology results from Planck
April 13, 2018
Friday noon seminar
Yacine Ali-Haimoud
New York University
Primordial Black Holes in the era of Planck and LIGO
May 18, 2018
Friday noon seminar
Belokurov Vasily
University of Cambridge/CCA, NYC
Milky Way's stellar halo with Gaia
May 23, 2018
Wednesday colloquium
Brian Keating
UC San Diego
The Simons Observatory
 
WEDNESDAY COLLOQUIA
KICP Wednesday Colloquia: Unless otherwise noted, all talks are held in ERC 161 at 3:30 PM on Wednesdays. A reception will be held in the ERC 401 following the talk.

  • January 10, 2018 | 3:30 PM | ERC 161
    From Emergent Gravity to Dark Energy and Dark Matter
    Erik P. Verlinde, University of Amsterdam

    Video
    The observed deviations from the laws of gravity of Newton and Einstein in galaxies and clusters can logically speaking be either due to unseen dark matter or due to a change in the way gravity works. Until recently there was little reason to doubt that general relativity correctly describes gravity in these circumstances. In the past few years insights from black hole physics and string theory have lead to a new theoretical framework in which the gravitational laws are derived an underlying microscopic quantum description of spacetime. An essential ingredient in the derivation of the Einstein equations is that the quantum entanglement of the vacuum obeys an area law, a condition that is known to hold in Anti-de Sitter space. In a Universe that is dominated by positive dark energy, like de Sitter space, the microscopic entanglement entropy contains, in addition to the area law, a volume law contribution whose total contribution equals the Bekenstein-Hawking entropy associated with the cosmological horizon. We will argue that this extra volume law contribution leads to modifications in the emergent laws of gravity, and provide evidence for the fact that these modifications explain the observed phenomena in galaxies and clusters currently attributed to dark matter. We end with a discussion of the possible implications for early cosmology, the CMB and structure formation.
  • January 24, 2018 | 3:30 PM | ERC 161
    Citizen Science Frontiers: Efficiency, Engagement, and Serendipitous Discovery with Human-Machine Systems
    Laura Trouille, The Adler Planetarium and Northwestern University

    Video
    The Zooniverse is the world's largest and most successful scientific crowdsourcing platform, engaging more than 1.6 million volunteers in tasks including classifying galaxies, discovering planets, transcribing artist's notebooks, and tracking resistance to antibiotics. Processing our increasingly large datasets poses a bottleneck for producing real scientific outcomes. Citizen science - engaging the public in research - provides a solution, particularly when coupled with machine learning algorithms and sophisticated task allocation. Faced with a rapidly growing demand for citizen science projects, Zooniverse launched its 'Project Builder' which allows you, the researcher, to build your own project in-house for free using the Zooniverse infrastructure and tools. In this talk I will discuss the frontiers of citizen science, including Zooniverse innovations in human-machine integration coupled with community engagement -- and the related open questions. I will also provide a brief tutorial on building your own crowdsourcing project.
  • February 7, 2018 | 3:30 PM | ERC 161
    CANCELLED
    Gauge-field inflation and the origin of the matter-antimatter asymmetry
    Peter Adshead, University of Illinois at Urbana-Champaign

    The basic inflationary paradigm is in good shape. On the one hand, the observed density fluctuations are adiabatic, gaussian and are red-tilted---characteristics in general agreement with simple models built from scalar fields. On the other hand, B-mode polarization of the cosmic microwave background sourced by primordial gravitational waves, the so-called smoking-gun signature of inflation, remains elusive. Upcoming and planned experiments will make increasingly precise B-mode measurements, potentially putting the inflationary paradigm through a stringent test. In this talk, I describe a new class of inflationary scenarios which utilize gauge fields to generate inflationary dynamics in the early universe. Beyond simply providing yet another model for inflation, these scenarios furnish unique observational imprints which distinguish them from standard scalar-field scenarios. In particular, these scenarios generically result in large-amplitude, chiral gravitational waves and provide counterexamples to the standard claim that an observable tensor-to-scalar ratio requires inflation at the grand unification scale, as well as super-Planckian excursions of the inflaton. In addition I discuss how these chiral gravitational waves may be responsible for the matter-antimatter asymmetry of the Universe.
  • February 21, 2018 | 3:30 PM | ERC 161
    Discovering the Highest Energy Neutrinos Using a Radio Phased Array
    Abby Vieregg, The University of Chicago

    Ultra-high energy neutrino astronomy sits at the boundary between particle physics and astrophysics. The detection of high energy neutrinos is an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. IceCube has detected astrophysical neutrinos at lower energies, but the best limit to date on the flux of ultra-high energy neutrinos comes from the ANITA experiment, a NASA balloon-borne radio telescope designed to detect coherent radio Cherenkov emission from cosmogenic ultra-high energy neutrinos. The future of high energy neutrino detection lies with ground-based radio arrays, which would represent an large leap in sensitivity. I will discuss a new radio phased array design that will improve sensitivity enormously and push the energy threshold for radio detection down to overlap with the energy range probed by IceCube.
  • March 14, 2018 | 3:30 PM | ERC 161
    Dark Matter in the Universe
    Katherine Freese, University of Michigan
    Note: Reception at 4:30 PM in the ERC 401.

    “What is the Universe made of?” This question is the longest outstanding problem in all of modern physics, and it is one of the most important research topics in cosmology and particle physics today. The bulk of the mass in the Universe is thought to consist of a new kind of dark matter particle, and the hunt for its discovery in on. I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Neutrinos only constitute ½% of the content of the Universe, but much can be learned about neutrino properties from cosmological data. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos. WIMPs are a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak-scale interactions with ordinary matter. There are multiple approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; with astrophysical searches for dark matter annihilation products, and upcoming searches with the James Webb Space Telescope for Dark Stars, early stars powered by WIMP annihilation. Current results are puzzling and the hints of detection will be tested soon. At the end of the talk I'll briefly turn to dark energy and its effect on the fate of the Universe.
  • March 28, 2018 | 3:30 PM | ERC 161
    TBA
    Luca Grandi, The University of Chicago

    TBA
  • April 4, 2018 | 3:30 PM | ERC 161
    (KICP) Colloquium
    Rush D Holt, AAAS
    Note: Reception at 4:30 PM in the ERC 401.
  • April 11, 2018 | 3:30 PM | ERC 161
    Cosmology results from Planck
    Silvia Galli, IAP
    Note: Reception at 4:30 PM in the ERC 401.
  • May 23, 2018 | 3:30 PM | ERC 161
    The Simons Observatory
    Brian Keating, UC San Diego
    Note: Reception at 4:30 PM in the ERC 401.

 
FRIDAY NOON SEMINARS
KICP Friday noon seminar: Unless otherwise noted, all talks are held in ERC 401 at Noon on Fridays.

  • January 12, 2018 | 12:00 PM | ERC 401
    Topics in weak lensing
    Patricia Larsen, Argonne National Laboratory

    Gravitational weak lensing has emerged in recent years as a powerful probe of cosmology, giving important constraints on both dark and luminous matter. This has led to a number of ambitious future surveys, which promise to revolutionise the field if theoretical challenges can be met. In this talk I will discuss some of my recent work in the field of weak lensing, spanning a range of topics including combined probe analysis, intrinsic alignment contamination and delensing.
  • January 19, 2018 | 12:00 PM | ERC 401
    Discussion on old and new mechanisms of leptogenesis
    Jessica M Turner, Fermi National Accelerator Laboratory

    In the first half of the talk, I will present preliminary results which indicate the scale of thermal leptogenesis may be several orders of magnitude lower than previously thought. In the second half of this talk I will present a mechanism of leptogenesis which is based on the vacuum CP-violating phase transition. This approach differs from classical thermal leptogenesis as a specific seesaw model, and its UV completion, need not be specified. The lepton asymmetry is generated via the dynamically realised coupling of the Weinberg operator during the phase transition. This mechanism provides strong connections with low-energy neutrino experiments.
  • January 26, 2018 | 12:00 PM | ERC 401
    Mass' not the only thing: Secondary effects in the galaxy-halo connection
    Yao-Yuan Mao, University of Pittsburgh

    Dark matter halos are the building blocks of our universe. The story we have been telling is that the galaxies live in halos, and that brighter galaxies live in bigger halos. This story is mostly consistent with our observation and hydrodynamical simulations, and has shed light on our understandings of galaxy formation and evolution. However, it is also clear that this simple, zeroth-order galaxy-halo connection is not the whole story. The assembly history of halos affects the galaxies reside in, and also affects the clustering properties of halos. This effect, usually known as "assembly bias," has brought new challenges to our ability to accurately model the galaxy-halo connection. A class of galaxy-halo connection models that take assembly bias into account has emerged, but it at the same time highlights the complex nature of assembly bias. In this talk I will discuss a few different aspects of assembly bias, focusing on how it affects the galaxy-halo connection and also its implications.
  • February 2, 2018 | 12:00 PM | ERC 401
    High redshift 21cm intensity mapping Past, Present, and Future
    Daniel Jacobs, Arizona State University

    The redshifted 21 cm line from neutral hydrogen provides a direct, cosmological scale, probe of the epochs of reionization and heating. In the past decade, multiple experimental arrays have worked towards detection and characterization of this spectral line signal at redshifts 6 and higher. HERA is a second generation instrument probing 21cm emission and absorption at redshifts from 6 to 20. The use of large static dishes provides sensitivity which is predicted to be roughly an order of magnitude larger than first generation experiments while advances in instrumentation and technique aim for reduced foreground contamination. The raw sensitivity provided by dishes is high enough that forecasts of astrophysical parameter constraint precision is limited mainly by model uncertainty not sensitivity, and that for the first time direct imaging of features is theoretically possible. HERA is proceeding with construction while observing in parallel with new dishes being added as they become available. The 2017-2018 observing season with 40 dishes is forecasted to have roughly double the sensitivity of previous experiments. Here we report the ongoing commissioning of this array and present early results of experiments in calibration and imaging.
  • February 9, 2018 | 12:00 PM | ERC 401
    The impact of massive neutrinos on cosmological observables
    Francisco Villaescusa-Navarro, Center for Computational Astrophysics

    Neutrinos are one of the most mysterious particles in nature. The discovery that they are massive has revolutionized our understanding of fundamental physics. Unfortunately, we still don't know their nature, masses or hierarchy. A worldwide effort is underway trying to answer these questions through laboratory experiments. In this seminar I will show how neutrino's unique nature leaves signatures on many different cosmological observables such as the properties of matter, halos, galaxies, voids, redshift-space distortions, the Lya-forest, baryonic acoustic oscillations and 21cm. I will discuss how those signatures can be used to weigh neutrinos and what are the main problems to obtain an unbiased measure of their masses.
  • February 16, 2018 | 12:00 PM | ERC 401
    Project 8: Towards a Direct Measurement of the Neutrino Mass with Tritium Beta Decays
    Noah S Oblath, Pacific Northwest National Laboratory

    Cyclotron Radiation Emission Spectroscopy, a frequency-based method for deter- mining the energy of relativistic electrons, has recently been demonstrated by the Project 8 collaboration. Applying this technique to the tritium endpoint provides a new avenue for measuring the absolute mass-scale of the neutrino. The proof of principle was done in a small waveguide detector using gaseous 83mKr as a source of monoenergetic electrons. As the next step towards a neutrino mass measurement, we are upgrading the existing detector to operate using a molecular tritium source, and to have enhanced radiofrequency properties. These upgrades are the next research and development steps needed to design a larger scale experiment that will approach the existing neutrino mass limits. I will discuss the expected physics reach of this second phase of Project 8 with molecular tritium, based on data from its commissioning with 83mKr. I will also present the plans for Phases III and IV, and the challenges being addressed for each phase.
  • April 13, 2018 | 12:00 PM | ERC 401
    Primordial Black Holes in the era of Planck and LIGO
    Yacine Ali-Haimoud, New York University
  • May 18, 2018 | 12:00 PM | ERC 401
    Milky Way's stellar halo with Gaia
    Belokurov Vasily, University of Cambridge/CCA, NYC

 
SPECIAL SEMINARS


 
OPEN GROUP SEMINARS


 
THURSDAY LUNCH DISCUSSIONS
KICP's Thunch: KICP Cosmology Lunch (Thunch) Weekly on Thursdays, Noon, ERC 401A.

Please join us for an informal lunch discussion, led by KICP fellows, of recent news and papers in cosmology. Topics range from experiment and observations to theory in all areas of KICP science. To submit or view papers for this week's Thunch please visit the Thunch website.


 
ASTRONOMY COLLOQUIA
Colloquia of the Department of Astronomy & Astrophysics: Unless otherwise noted, all talks are held in ERC 161 at 3:30 PM on Wednesdays. A reception will be held in Hubble Lounge (ERC 501) following the talk.

  • January 17, 2018 | 3:30 PM | ERC 161
    WFIRST: Where Things Stand with the First Exoplanet Direct Imaging Flight Mission
    Maggie Turnbull, SETI

    The WFIRST mission will be the first demonstration of exoplanet coronagraphy in space, and is intended to demonstrate several key technologies that are on the critical path to larger missions that will eventually find and spectrally characterize planets that could be habitable to life as we know it. WFIRST entered Phase A in January of 2016, and is expected to enter Phase B in April of this year. This talk will describe the entertaining story of how this mission came to be, where things currently stand in terms of predicted imaging performance, the potential for a starshade rendezvous mission, and what to expect for guest observer opportunities. I'll also describe how the two coronagraph science teams are working to maximize the scientific output of what is categorized as a "technology demonstration" instrument. Finally, I'll offer some of my personal take-aways from the experience of watching such a large and challenging mission come together.
  • January 31, 2018 | 3:30 PM | ERC 161
    The Basis for Cosmic Ray Feedback
    Ellen Zweibel, University of Wisconsin-Madison

    There is strong observational and theoretical evidence that star formation in galaxies is inherently self limiting, and that the interaction of galaxies with their environments plays a significant role in galactic evolution. Cosmic rays - the relativistic particles that pervade our galaxy and account for about 1/3 of the energy density in the interstellar medium - have emerged as a likely agent of these forms of feedback. The basis of cosmic ray feedback is scattering of cosmic rays by plasma waves, a microscale process that ultimately transfers energy and momentum between cosmic rays and thermal gas. The image, from Ruszkowski, Yang, & Zweibel 2017, shows a simulation of an outflow driven from a galaxy by this process.
  • February 14, 2018 | 3:30 PM | ERC 161
    Galactic Winds: Phenomenology, Physics, and Implication
    Tim Heckman, Johns Hopkins University

    I will discuss the nature of galactic winds driven by the energy and momentum supplied by populations of massive stars. I will give an overview of the basic physical processes that lead to the formation and propagation of galactic winds. I will then give a "guided tour" of the multi-phase galactic wind driven by the prototypical starburst galaxy M 82. Next, I will describe how the basic parameters of winds can be inferred from the data and summarize the systematic dependences of these parameters on the key properties of the galaxy and the starburst. I will then discuss how well these systematic properties compare to assumptions used in cosmological simulations of galaxy evolution. Finally, I will describe the implications of winds for galaxy evolution, specifically in the context their impact on the circum-galactic medium and on the chemical evolution of galaxies.
  • February 28, 2018 | 3:30 PM | ERC 161
    Heavy element synthesis in the Universe
    Enrico Ramirez-Ruiz, University of California, Santa Cruz
    Note: Refreshments served at 4:30 PM, Hubble Lounge

    The source of about half of the heaviest elements in the Universe has been a mystery for a long time. Although the general picture of element formation is well understood, many questions about the nuclear physics processes and particularly the astrophysical details remain to be answered. Here I focus on recent advances in our understanding of the origin of the heaviest and rarest elements in the Universe.
  • March 7, 2018 | 3:30 PM | ERC 161
    TBA
    Bekki Dawson, Pennsylvania State University
    Note: Refreshments served at 4:30 PM, Hubble Lounge

 
ASTRONOMY TUESDAY SEMINARS

  • January 16, 2018 | 12:00 PM | ERC 576
    Surveying Spotted Stars with Photometric, Spectroscopic, and Interferometric Observations
    Rachael Roettenbacher, Stockholm University

    For stars with convective outer layers, stellar magnetism manifests as dark starspots -- localized regions of stifled convection. Starspots affect measurements of fundamental stellar parameters, including temperature and radius, which lead to inaccurate estimates of age and mass. Additionally, starspots have been shown to mimic and obscure detections of planets. By imaging stellar surfaces, we begin to disentangle the signatures of stellar magnetism. The imaging efforts discussed here feature aperture synthesis imaging using interferometric data collected with the Michigan Infrared Combiner (MIRC) at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array with sub-milliarcsecond resolution. We characterize active RS CVn binary systems and detect magnetic structures across the surface of the giant primary stars. We compare the results to simultaneous Doppler and light curve inversion imaging. The observed global regions of suppressed convection likely affect stellar parameter estimates by altering the structure of the photosphere. Extensions of this study will survey spotted stars in order to understand how stellar magnetism affects stellar parameters, impacts the evidence of companions and their characterization, accounts for long-term changes in the flux of active stars, and differs from the Sun for stars with large convective envelopes.
  • January 30, 2018 | 12:00 PM | ERC 576
    The deaths of galaxies and the growth of supermassive black holes: implications for galaxy evolution and tidal disruption events
    Decker French, Carnegie Observatories

    Post-starburst (or "E+A") galaxies are in transition between star-forming galaxies and early-types, and represent a clear path for galaxies to transform from star-forming to quiescence. Many show signs of a recent galaxy-galaxy merger and a newly-evolved stellar bulge, and most have LINER-like emission, which may indicate low luminosity AGN activity. Thus, the study of this short-lived phase of galaxy evolution can address the connections among mergers, star formation history, and the evolution of the nucleus as a galaxy evolves onto the red sequence. Surprisingly, we have discovered that many these galaxies have significant reservoirs of molecular gas, yet low dense gas fractions. We have also found that post-starburst galaxies host a disproportionate number of Tidal Disruption Events, in which a star is accreted onto the black hole. The recent starburst in these galaxies allows us to put strong constraints on the details of their recent star formation histories, and to place them on a timeline post-burst. I will discuss these results and other new work detailing how their stellar populations, gas content, and black hole properties evolve.
  • February 13, 2018 | 12:00 PM | ERC 576
    Relativistic Jets: Particle Accelerators of the Universe
    Maria Petropoulou, Princeton University

    The image shows an artist impression of the quasar ULAS J1120+0641

    Image credit: ESO/M. Kornmesser
    Relativistic jets, i.e., collimated outflows of plasma traveling with speeds approaching the speed of light, are ubiquitious in the Universe. They are unique laboratories for studying the physics of magnetized plasmas, particle acceleration, and radiation processes in extreme conditions that can never be achieved with terrestrial experiments. Some of the most powerful astrophysical jets are those emerging from the centers of active galaxies (AGN). It is commonly accepted that AGN jets can accelerate particles to ultra-relativistic energies which then radiate up to TeV energies. Yet, there are many unresolved issues with this well established paradigm: How is the jet energy converted into radiation? Are the radiating particles electrons or protons? Where and how are these particles accelerated? In this talk, I will discuss how we can combine multiple messengers, such as photons and neutrinos, with state-of-the-art numerical simulations to obtain insights into the physical processes operating in relativistic jets. The image shows an artist impression of the quasar ULAS J1120+0641 Image credit: ESO/M. Kornmesser
  • February 20, 2018 | 12:00 PM | ERC 576
    Making a Universe with Axions and Inflatons
    Chanda Prescod-Weinstein, University of Washington

    How can new approaches to quantum fields illuminate astrophysics on all scales? The discovery of the Higgs boson reinforces the possibility that other similar, scalar particles may exist in nature and could drive cosmological inflation. In this talk, I will discuss one such dark matter and sometime inflaton candidate, the axion. I will talk about the increasingly popular claim that dark matter axions form an exotic state of matter called a Bose-Einstein condensate and my own work on this idea. This unique intersection of early universe cosmology with an idea from atomic physics is but one example of the exciting ways in which we are still exploring the dynamics of established and proposed particles in the early universe, especially those that may drive inflation. Thus I will also describe efforts to understand different inflationary models through the lens of reheating -- particle production at the end of inflation -- and how techniques developed for this work can be applied in other arenas such as studying modified gravity. I will discuss how these ideas make contact with data from direct detection experiments and astrophysical observations, and my participation in the planned space missions STROBE-X and eXTP.

 
ASTRONOMY SPECIAL SEMINARS

  • February 8, 2018 | 12:00 PM | ERC 576
    Debris Disks as Probes of Planetary System Evolution
    Meredith MacGregor, Carnegie Department of Terrestrial Magnetism

    At least 20% of nearby main sequence stars are surrounded by disks of dusty material resulting from the collisional erosion of planetesimals, larger bodies similar to asteroids and comets in our own Solar System. The resulting dust can be observed via scattered light at visible to near-infrared wavelengths or thermal emission at mid-infrared to millimeter wavelengths. Since the dust-producing planetesimals are expected to persist in stable regions like belts and resonances, the locations, morphologies, and physical properties of dust in these "debris disks" provide probes of planet formation and subsequent dynamical evolution. Observations at millimeter wavelengths are especially critical to our understanding of these systems, since the large grains that dominate emission at these long wavelengths do not travel far from their origin and therefore reliably trace the underlying planetesimal distribution. I will present ongoing work that uses observations of the angularly resolved brightness distribution and the spectral dependence of the flux density to constrain both the structure and grain size distribution of nearby debris disks. In particular, I will show new ALMA observations that place constraints on the position, width, surface density gradient, and any asymmetric structure of several well-known debris disks (including Fomalhaut, HD 32297, and HD 61005). Together these results provide an exciting foundation to investigate the dynamical evolution of planetary systems through multi-wavelength observations of debris disks.