ASD Colloquium Series - Spring 2025
ASD Colloquium Series - Spring 2025
The Astrophysics Science Division colloquia occur on Tuesdays at 3:45 pm in a Hybrid format. For in person attendees, the colloquia will be held in building 34, room W150 (unless otherwise noted), with an opportunity to meet the speaker at 3:30 pm. Virtual attendees should use connection information in the calendar invites.
Below is the list of scheduled talks for this period. Confirmed speakers are shown in bold face, while tentatively scheduled speakers are listed in normal face.
Schedules from past colloquium seasons are available.
Contact: Scott C. Noble
| January | |
|---|---|
| Jan 7 | Binary Black Hole Formation: A Multimessenger, Multiband Puzzle Katelyn Breivik (Carnegie Mellon University) |
| Jan 14 | No Colloquium - Winter AAS Meeting |
| Jan 21 | No Colloquium - MLK/Inaugaration Day |
| Jan 28 | TBD |
| February | |
| Feb 4 | Special Location: B34, W130 Precision interferometry: Towards exo-Earth imaging and 30m-class telescopes Steve Ertel (Steward Observatory and the Large Binocular Telescope Observatory) |
| Feb 11 | The colloquium is being canceled due to risk of inclement weather. The speaker has agreed to reschedule and visit us in the near future. Standing Out from The Crowd: Finding Supermassive Black-hole Binaries in Gravity & Light Stephen Taylor (Vanderbilt University) |
| Feb 18 | No Colloquium - Washington's Birthday |
| Feb 25 | Supermassive Black Holes Through the Kaleidoscope Krista Lynne Smith (Texas A&M University, College Station, USA) |
| March | |
| Mar 4 | Special Location: B34, W150 Looking at Infrared Background Radiation Anisotropies with Spitzer: Large-scale Anisotropies and Their Implications Sasha Kashlinsky (NASA GSFC) |
| Mar 11 | Special Location: B34, W150 Reflecting on Accretion in Neutron Star Low-Mass X-ray Binaries Renee Ludlum (Wayne State University) |
| Mar 18 | TBD Klaus Pontoppidan (STScI/JPL) |
| Mar 25 | TBD Alexander Cooper (Oxford) |
| April | |
| Apr 1 | TBD Anna Ho (Cornell) |
| Apr 8 | TBD |
| Apr 15 | TBD Chris Richardson (Elon U) |
| Apr 22 | TBD Grace Telford (Princeton) |
| Apr 29 | TBD Julia Roman-Duval (STScI) |
May |
| May 6 | TBD Nico Cappelluti (U Miami) |
| May 13 | TBD |
| May 20 | TBD Chiara Mingarelli (Yale) |
| May 27 | No Colloquium - Memorial Day |
| June | |
| June 3 | TBD Margaret Lazzarini CSU-LA) |
Abstract
Binary star populations play a pivotal role in nearly all subfields of astronomy and cosmology, yet the quantitative details of how they evolve are still poorly described. This is due both to a wide array of uncertain physical interaction processes like mass exchange and supernova explosions that can work in compounding ways and a lack of large data sets that contain binary populations across different evolutionary phases. In this talk, I'll review how binary-star interactions shape stellar populations hosting black holes and introduce recent and upcoming gravitational wave and electromagnetic survey data releases that can be used to constrain models for binary evolution. I'll finish with a discussion of the discovery of a new population of compact objects in binaries with stellar companions made by the Gaia satellite that offer a unique window into compact object formation.
Abstract
Compared to filled-aperture telescopes, astronomical optical long-baseline interferometry typically provides higher angular resolution and higher-precision spatial measurements at the cost of fidelity, dynamic range, and consequently contrast of reconstructed images. I use the term precision interferometry to refer to efforts of overcoming this limitation through more precise measurements of the classical interferometric observables (visibilities and closure phases) or though circumventing them altogether using nulling or Fizeau (imaging) interferometry. Over the past almost two decades, these efforts have enabled the spatially resolved observations of the habitable zones and closer in of planetary systems with a sensitivity to detect circumstellar, exozodiacal dust. This dust poses both an opportunity to study the architectures and dynamics of planetary systems near their habitable zones and a potential obstacle to directly imaging rocky, habitable-zone planets. It's study is thus crucial for enabling and preparing for a future exo-Earth imaging mission such as the Habitable Worlds Observatory. I will review our work on exozodiacal dust with the Large Binocular Telescope Interferometer (LBTI) and the Very Large Telescope Interferometer (VLTI). I will further present our efforts to enable high-fidelity imaging at the angular resolution of a 23m telescope with the LBTI for general astronomical observations. This work makes the LBTI a critical pathfinder for future 30m-class telescopes. Both exo-Earth imaging and the completion and exploitation of 30m-class telescopes are major priorities of the US community as outlined in the National Academy's Astro2020 Decadal Survey. I will then close the loop and conclude my talk by outlining our efforts to obtain the first direct-imaging detection of a rocky, habitable-zone planet around a nearby, Sun-like star with the LBTI.
Abstract
The Universe is thrumming with gravitational waves. June 2023 brought the first evidence for an all-sky background of nanohertz-frequency gravitational waves, discovered by collaborations including the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and groups in Europe, Australia, India, and China. This was an endeavor decades in the making, requiring painstakingly precise timing observations of scores of millisecond pulsars across the Milky Way using flagship radio telescopes. While the results from separate groups are consistent with one another—and the leading interpretation of a cosmic population of supermassive black-hole binaries as the source—the observations provoke many new questions. Do the results imply a population of binaries more massive than expected? What are the observational milestones as the first resolvable massive black-hole binary signals come into focus? Can we link these signals to host galaxies and leverage electromagnetic counterparts to do multi-messenger astronomy with massive black holes? In this talk, I will chart the path to discovery, reflect on what we have learned during our year+ since our announcement, and explore the exciting opportunities ahead—including the role of next-generation instruments in expanding our pulsar network to explore the low-frequency gravitational-wave and supermassive binary black-hole landscape.
Abstract
The space-time distortion caused by supermassive black holes provides a unique laboratory for violent physical processes like stellar tidal disruption, highly relativistic jets, and turbulent accretion flows. Synthesizing observations across many wavelengths and studying their time variability at slow and rapid timescales promises a new, dynamic, thorough understanding of how black holes form and grow, how they consume material, how they construct powerful relativistic jets, and how they bend the evolution of galaxies to a path that matches our observations of the Universe. I will discuss how both high-resolution radio imaging surveys of outflows and star formation and timing observations with breakthrough instruments like the NICER instrument on the ISS and the TESS exoplanet-hunting missions have provided new intersectional insights and promise a fertile new temporal phase space for exploring the detailed phenomenology and cosmological implications of active galactic nuclei. In my talk, I will discuss results from a 22 GHz radio imaging survey of hundreds of BAT AGN and implications for both the origin of radio emission their cores and AGN feedback on galaxy-wide scales. I will also discuss time domain investigations of accretion and jets with the Transiting Exoplanet Survey Satellite, and the future of high-cadence optical timing for both advances in accretion physics and detection of multimessenger systems of binary supermassive black holes.
Abstract
We use Spitzer/IRAC deep-exposure data covering two significantly larger than before sky areas to construct maps suitable for evaluating source-subtracted fluctuations in the cosmic infrared background (CIB). The maps are constructed using the self-calibration methodology eliminating artifacts to sufficient accuracy, and subset maps are selected in each area containing approximately uniform exposures. These maps are clipped and removed of known sources and then Fourier transformed to probe the CIB anisotropies to new larger scales. The power spectrum of the resultant CIB anisotropies is measured from the data to >1°, revealing the component well above that from remaining known galaxies on scales >1′. The fluctuations are demonstrated to be free of Galactic and solar system foreground contributions out to the largest scales measured. We discuss the proposed theories for the origin of the excess CIB anisotropies in light of the new data. Out of these, the model where the CIB fluctuation excess originates from the granulation power due to LIGO-observed primordial black holes as dark matter appears most successful in accounting for all observations related to the measured CIB power amplitude and spatial structure, including the measured coherence between the CIB and unresolved cosmic X-ray background (CXB). Finally we point out the use of the data to probe the CIB-CXB cross power to new scales and higher accuracy. We also discuss the synergy of these data with future CIB programs at shorter near-IR wavelengths with deep wide surveys and subarcsecond angular resolution as provided by Euclid and Roman space missions.
Abstract
Neutron star (NS) low-mass X-ray binaries (LMXBs) accrete via Roche-lobe overflow from a stellar companion of roughly 1 solar mass. The accretion disk surrounding the NS in these systems can be externally illuminated by X-rays that are reprocessed by the accreting material and re-emitted as the reflection spectrum, which is comprised of emission lines superimposed onto a reprocessed continuum. Due to proximity of the inner region of the disk to the compact accretor, strong gravity and relativistic effects are imparted to the reflection spectrum. Modeling of these effects allows us to infer properties of the NS itself (such as magnetic field strength and limits on the radial extent), as well as other aspects of the system like accretion and illumination source geometry, ionization state and composition of the material, and density of the disk. Much has been learned about these systems using advanced X-ray missions like NICER and NuSTAR, which can obtain spectra from bright sources without distortion. The recent successful operation of a microcalorimeter in space aboard XRISM provides high-energy resolution observations of several persistently accreting NSs. These datasets reveal undeniable structure within the prominent Fe K line region of the reflection spectrum and provide further insights into the accretion geometry of these systems. I will highlight what has been learned about NS LMXBs via reflection modeling over the last decade and prospects for further insights.