Astrophysics Science Division
Astrophysics Science Division Colloquium Series Schedule: Fall 2023

ASD Colloquium Series - Fall 2023

ASD Colloquium Series - Fall 2023

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.

Schedules from past colloquium seasons are available.

Contact: Scott C. Noble


Sep 12 A population of ultra-long period magnetars and its links to fast radio bursts
Paz Beniamini (Open University of Israel)
Sep 19 No Colloquium
Sep 26 Special Location: B34, W120B
Early Results from the CLASS 40 GHz Survey of the Cosmic Microwave Background
Joseph Eimer (Johns Hopkins University)


Oct 3 No Colloquium - 600 Townhall Meeting
Oct 10 No Colloquium - Indigenous People's Day Weekend
Oct 17 The Search for Other Earths
Megan Bedell (CCA/Flatiron)
Oct 24 Special Location: B34, W305
Searching for Black Holes From the Nearby to the Faraway Universe
Fabio Pacucci (Black Hole Initiative, CfA, Harvard/Smithsonian)
Oct 31 The NASA SMD Bridge Program and How You Can Get Involved
Steven Villanueva (NASA GSFC, 667)


Nov 7 Special Location: B34, W120A
Long-period Radio Transients
Natasha Hurley-Walker (ICRAR)
Nov 14 The Nanohertz Gravitational Wave Background: How we found it & what we can learn from it
Joseph Simon (University of Colorado Boulder)
Nov 21 No Colloquium - Thanksgiving Week
Nov 28 Looking for cracks in the cosmological model
Jo Dunkley (Princeton University)


Dec 5 Special Location: B34, E215
Worlds & Suns in Context: The Role of Age and Environment
Melinda Soares-Furtado (University of Wisconsin-Madison)
Dec 6 Special Day & Time: 10:45 AM
GammaTPC: a novel next generation Compton telescope
Thomas Shutt (KIPAC, Stanford University)
Dec 12 Fred Adams (U. Michigan)
Dec 19 Roy Kilgard (Wesleyan)
Dec 26 No Colloquium - Winter Holidays

Preview the Spring 2024 season.

A population of ultra-long period magnetars and its links to fast radio bursts
Paz Beniamini
Open University of Israel
Tuesday, Sep 12, 2023


Recent findings suggest that there is a large group of radio-loud sources with long periods whose emission cannot be easily explained by rotation losses. These sources have been difficult to detect in the past due to built-in biases in existing radio campaign search strategies. In this study, we will focus on recently discovered candidates and propose that they are likely to be ultra long period magnetars (ULPMs). By studying these sources along with previously detected objects, we have identified at least several potential candidates for Galactic ULPMs. The detection of these objects suggests that there could be hundreds to thousands of similar objects in our Galaxy. The large number of ULPM candidates, along with their cooling age limits, Galactic offsets, timing stability, and dipole spindown limits, all suggest that these objects are substantially older than confirmed Galactic magnetars and that their formation channel is a common one. The existence of ULPMs implies the widespread survival of magnetar-like fields for several million years, which is distinct from the behavior observed in confirmed Galactic magnetars. ULPMs may also represent a second class of Fast Radio Burst (FRB) progenitors that exhibit very long (tens to hundreds of days) periodic activity windows. I will briefly describe the evidence in favor of this connection and the potential underlying mechanisms driving FRB producing magnetars to such long periods.

Early Results from the CLASS 40 GHz Survey of the Cosmic Microwave Background
Joseph Eimer
Johns Hopkins University
Tuesday, Sep 26, 2023


Measurement of the largest angular scale features of the cosmic microwave background (CMB) polarization is a powerful way to constrain the optical depth to reionization, and search for the signature of inflation through the detection of primordial B-modes. In this talk, I present an analysis of maps covering nearly 75% of the sky made from the ground-based 40GHz channel of the Cosmology Large Angular Scale Surveyor (CLASS) from August 2016 to May 2022. Using fast front-end polarization modulation from the Atacama Desert, we show this channel achieves higher sensitivity than the analogous frequencies from satellite measurements in the range 10 < l < 100. In combination with other data, these new maps improve our understanding of the polarized synchrotron spectral energy distribution — critical for isolating cosmological signals from galactic astrophysics. Beyond linear polarization, we place a new upper limit on a background of circular polarization. These results establish a new standard for recovery of the largest-scale CMB polarization from the ground and signal exciting possibilities when the higher sensitivity and higher frequency CLASS channels are included in the analysis.

The Search for Other Earths
Megan Bedell
Tuesday, Oct 17, 2023


Detecting a true Earth twin exoplanet (an Earth-mass planet orbiting a Sun-like star within the habitable zone) has recently become feasible for the first time thanks to advances in observational technology. I will give an overview of the motivations and challenges in achieving this goal, and in discovering new exoplanets more generally. In particular, I'll focus on the Terra Hunting Experiment, an upcoming ground-based radial velocity (RV) survey dedicated to the search for Earth twins. I will discuss the complementarity of RV surveys like this one with current and future NASA missions. I will also present recent work on designing surveys and developing statistical tools for measuring sub-meter-per-second amplitude motions in distant stars.

Searching for Black Holes From the Nearby to the Faraway Universe
Fabio Pacucci
Black Hole Initiative, CfA, Harvard/Smithsonian
Tuesday, Oct 24, 2023


I will provide an overview of our quest to explore, with theory and observations, undetected populations of black holes, proceeding from the nearby to the faraway Universe. First, I will unveil a new multiwavelength observational campaign likely leading to the discovery of the second closest supermassive black hole in the Milky Way satellite Leo I. I will then describe the 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 investigate why we may be missing a significant fraction of this population. Furthermore, based on JWST data of galaxies hosting black holes at z=4-7, I will present a new, detailed statistical analysis that reveals a high-z M_bh-M_star relation that deviates at >3sigma confidence level from the local relation. Black holes are overmassive by 10-100 times compared to their low-z counterparts; this fact is not due to a selection effect in surveys. I will then conclude with the observational properties of the sources that have started the reionization at z ~ 20-30: the first population of stars and black holes, and how we may soon detect them directly.

Searching for Black Holes From the Nearby to the Faraway Universe
Steven Villanueva
Tuesday, Oct 31, 2023


The NASA SMD Bridge Program is a new grant to create long-term research and mentoring partnerships between scientists at NASA centers and faculty at institutions historically underfunded by NASA. The grant proposals will be led by the faculty and co-written with a NASA partner. We are actively looking for volunteers at NASA centers to participate. These proposals must include paid research positions for the faculty's students on research relevant to the NASA Science Mission Directorate (SMD). Our program also includes the SMD Bridge Seed Funding Program, which will fund faculty who need to create new connections or strengthen their existing partnerships to our NASA scientists. Bridge Program proposals will address the science, the partnership between the institution and NASA, and contain a plan for how the students will be mentored and trained during their time working with NASA.

Long-period Radio Transients
Natasha Hurley-Walker
Tuesday, Nov 7, 2023


Pulsars have long been known to produce periodic pulsed radio emission as they rotate with periods of milliseconds to seconds, generating radio waves that sweep across our line-of-sight. They allow us to probe extremes of magnetism, gravity, neutron star matter, and have been used to test general relativity to high precision. While the exact radio emission mechanism is not well-understood, they are thought to be jointly powered by their magnetic fields and fast rotation, persisting for millions of years before slowing to rotation rates (~minutes) that no longer generate radio waves (crossing the "death lines"). Magnetars, which are highly magnetized, young neutron stars, are known for their sporadic periodic bursts of X-rays, gamma-rays, and radio waves, believed to be triggered by intense magnetic activity.

Using the Murchison Widefield Array, we have detected two long-period radio transients, with periods of 18 and 22 minutes. Timing estimates place the most recently discovered source below the conventional death lines of physical mechanisms that produce radio emission from pulsars, or rescaled death lines for white dwarf pulsars. However, its long-lived activity makes it challenging to interpret as a magnetar. The sources' bright radio emission is therefore a puzzle which new observations with MeerKAT and new physical modelling is beginning to illuminate. I will describe the sources, show our current thinking on the origin of the radio emission, and conclude with future survey plans across a range of telescopes.

The Nanohertz Gravitational Wave Background: How we found it & what we can learn from it
Joseph Simon
University of Colorado Boulder
Tuesday, Nov 14, 2023


Pulsar timing data has recently uncovered evidence for a gravitational wave (GW) background, and the signal is consistent with the expectations for a cosmic population of binary supermassive black holes (SMBHs). In this talk, I will discuss the datasets and analyses that led to this discovery as well as interpretations of the signal for both SMBHs and more exotic GW sources. I will conclude by laying down the roadmap towards exploring the multi-messenger discovery space that is now accessible with this new window onto the Universe.

Looking for cracks in the cosmological model
Jo Dunkley
Princeton University
Tuesday, Nov 28, 2023


Recent observations of the cosmic microwave background are allowing us to scrutinize the 'Lambda - Cold Dark Matter' cosmological model, and to weigh in on possible cracks in this model that may be appearing from different astronomical observations. I will describe recent results from the Atacama Cosmology Telescope, and show how the relic CMB light can be used as a backlight to weigh cosmic structures and to map out the dark matter over half the sky. I will also describe near-term prospects for an improved view of the physics of the early universe from these new data, and longer term prospects from the upcoming Simons Observatory.

Worlds & Suns in Context: The Role of Age and Environment
Melinda Soares-Furtado
University of Wisconsin-Madison
Tuesday, Dec 5, 2023


In this talk, I discuss the interactions between stellar hosts and planetary companions, including the ejection and ingestion of stellar companions. Drawing insights from stellar evolutionary models and observational survey data (photometric and spectroscopic), I present my team's latest discoveries as we seek to identify unambiguous ingestion-derived chemical tracers. Such tracers make it possible to identify engulfment events long after the original event has transpired and offer a critical opportunity to probe bulk planetary composition. Looking forward, infrared space-based missions like the Nancy Grace Roman Space Telescope will soon make it possible to investigate young, free-floating planets for the presence of satellites. These data would help to further constrain the formation pathways and dynamical histories of these starless worlds.

GammaTPC: a novel next generation Compton telescope
Thomas Shutt
KIPAC, Stanford University
Tuesday, Dec 6, 2023


I will talk about GammaTPC, a new instrument concept for measuring astrophysical gamma rays in the MeV energy range. This is a largely unexplored energy range due in large part to the difficulty of measuring such photons. GammaTPC uses liquid argon time projection chamber (TPC) technology which builds on developments for dark matter and neutrinos, and holds the promise of an instrument that is both very large and highly sensitive. Core to GammaTPC is GAMPix, a new charge readout scheme that achieves fine-grained, low noise readout at very low power. I will discuss his and other challenges to fielding a liquid noble TPC in low Earth orbit, as well as the status of GammaTPC development.

Past Colloquia Schedules