Alexander W. Criswell

EMIT Postdoctoral Fellow | Vanderbilt University and Fisk University

About Me

EMIT Postdoctoral Fellow | Vanderbilt & Fisk Universities

PhD, Astrophysics | Minnesota Institute for Astrophysics
PhD Minor | Data Science in Astrophysics

Affiliations: LIGO, LISA, NANOGrav, UVEX Science Team

I am an Expanding Multimessenger Interdisciplinary Training (EMIT) postdoctoral fellow at Vanderbilt and Fisk Universities. My research interests include gravitational-wave data analysis across the spectrum (LIGO/LISA/NANOGrav), multimessenger follow-up to gravitational-wave events, scientific software development, and applying advanced statistical and data science approaches to astrophysical problems.

My Research: Gravitational-wave Astronomy through (Hierarchical) Bayesian Inference

Exploring the Milky Way with the Stochastic Gravitational-wave Foreground

from White Dwarf Binaries in LISA

LISA, a spaceborne gravitational wave detector expected to launch in the 2030's, will have millions of sources all present in the detector simultaneously. One example of this is the Milky Way Foreground: the overlapping, stochastic hum from all of the individually-unresolvable white dwarf binaries in the Milky Way. This signal is expected to be so loud that it sits above the LISA noise curve, and will comprise a significant contribution to the overall noise present in LISA.

However, it is also an astrophysical gravitational-wave signal arising from the population of white dwarf binaries in our Galaxy. I am developing a hierarchical Bayesian analysis to infer the spatial distribution of this old stellar population from the stochastic foreground signal, allowing us to probe the early history of the Milky Way when LISA flies.

I am also leading several additional projects focused on LISA — most involving undergraduate researchers — that range from exploring the stochastic signals from white dwarf binaries in Milky Way satellites, to determining the angular resolution of anisotropic searches for stochastic gravitational wave signals with LISA, to enabling simultaneous inference of multiple stochastic signals in LISA.

Constraining Neutron Star Composition with Gravitational Waves from
Binary Neutron Star Post-merger Remnants in LIGO

The majority of binary neutron star mergers are expected to result in a hypermassive remnant. These remnants emit gravitational waves that are highly informative as to neutron star composition, but are emitted at high (kHz) frequencies where the current-generation gravitational wave detectors are less sensitive. As a result, constraints on the nuclear equation of state from post-merger remnants was considered out-of-reach until the advent of next-generation detectors.

I led an interdisciplinary team to develop a hierarchical Bayesian analysis called BayeStack. This analysis leverages empirical relations derived from numerical relativity alongside chirp mass measurements from the inspiral itself to statistically stack small amounts of information from each individually undetectable post-merger remnant across a large population of mergers. The BayeStack analysis was shown via simulations to be able to achieve meaningful constraints on the neutron star equation of state with current generation detector sensitivity.

This work is published in Physical Review D.

Multimessenger Follow-up

Member of the UltraViolet EXplorer (UVEX) science team. UVEX has been selected as next NASA MIDEX mission: a space telescope that will provide crucial rapid-response, wide-field survey, and spectroscopic capabilities in the near and far ultraviolet (planned launch date: 2030). During the mission's proposal and selection proess, I contributed in-depth simulation and statistical treatment of the multimessenger follow-up prospects for UVEX concurrent with LIGO-Virgo-KAGRA observing runs O5 and O6. Following the selection of UVEX as the next NASA MIDEX mission, I have continued developing our capabilities and prospect estimates for multimessenger follow-up with UVEX.

I have also contributed to a study of the kilonova follow-up prospects for Nancy Grace Roman.

Scientific Software Development

The Bayesian LISA Inference Package (BLIP): Contributor, current lead developer.

UVEX-followup: Primary developer.

BayeStack: Primary developer.

Teaching

While at the University of Minnesota, I TA'd for the undergraduate introductory astronomy course as well as a graduate course in Bayesian Astrostatistics. Additionally, I was the instructor of record for the undergraduate introductory astronomy course (AST 1001) in Summer 2023. At Vanderbilt, I have stepped in as a guest lecturer/facilitator for courses in order of magnitude estimation and astrostatistics. I have taken dedicated coursework in pedagogical methods for teaching in higher education, and am a strong believer in inclusive, accessible teaching.

Outreach and Service

Outreach

I am currently taking a short hiatus from active outreach activities while I get settled in Nashville -- watch this space! In the meantime, I am supporting EMIT outreach activities, including engaging with undergraduate students in data science at Fisk University. Past activities include:

Coordinator for Outreach through Science and Art at the University of Minnesota, an interdisciplinary program that engages the public at the intersection of science and art.
Assistant and MC for Astronomy on Tap MPLS.
Co-founder and coordinator of Universe @ Home, a livestreamed outreach program during the pandemic.
Featured and contributing speaker for a number of outreach programs, including University of Minnesota Public nights, Universe in the Park, Skype a Scientist, and the Bell Museum's Spacefest.

Service

I currently serve as a member of the EMIT program steering committee and the NANOGrav Equity & Climate committee.
Past appointments include:

Graduate student representative to the UMN School of Physics and Astronomy Graduate Education Committee.
Organizer, Data Science in Multimessenger Astrophysics journal club.
Diversity, Equity, and Inclusion Co-chair as well as Social Media & Outreach Co-chair for the Gravitational Wave Early Career Scientists professional organization.
Student representative for the Data Science in Multimessenger Astrophysics 2020 Cohort.

Selected Publications

Criswell, A.W., et al. (2025), Templated Anisotropic Analyses of the LISA Galactic Foreground. Phys. Rev. D 111, 023025. arXiv:2410.23260

Rieck, S., Criswell, A.W., et al. (2024), A stochastic gravitational wave background in LISA from unresolved white dwarf binaries in the Large Magellanic Cloud. MNRAS 531 no. 2, 2642–2652. arXiv:2308.12437

Criswell, A.W., et al. (2025), Electromagnetic Follow-up to Gravitational Wave Events with the UltraViolet EXplorer (UVEX). Accepted in PASP. arXiv:2501.14109

Andreoni, I., Coughlin, M.W., Criswell, A.W., et al. (2024), Enabling Kilonova Science with Nancy Grace Roman Space Telescope. Astropart. Phys. 155, 102904

Criswell, A.W., et al. (2023), Needle in a Bayes Stack: a Hierarchical Bayesian Method for Constraining the Neutron Star Equation of State with an Ensemble of Binary Neutron Star Post-merger Remnants. Phys. Rev. D 107, 043021

Banagiri, S., Criswell, A., Kuan, T., Mandic, V., Romano, J., Taylor, S. (2021), Mapping the Gravitational-wave Sky with LISA: A Bayesian Spherical Harmonic Approach. MNRAS 507 no. 4, 5451–5462.

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