Women of Arecibo: Dr. Thankful Cromartie

Written by Thankful Cromartie, PhD

Dr. Cromartie on the Arecibo platform

Thankful Cromartie received her Ph.D. from the University of Virginia in May 2020, and is currently a NASA Einstein Postdoctoral Fellow at Cornell University. Born and raised in North Carolina, she received her B.S. in Physics in 2014 from the University of North Carolina at Chapel Hill. Thankful is hopelessly addicted to studying millisecond pulsars: finding them, timing them, and using them to probe fundamental physics.

Preface: I’m extremely grateful for the opportunity to share this personal reflection about my time at Arecibo; however, I want to emphasize that it is just that — personal. I am not among those most profoundly affected by the loss of Arecibo: the observatory’s staff, scientists who have worked with the telescope for decades, Puerto Rican students, and countless others. I’d also like to note that any opinions expressed here may not be shared by my employer or my scientific collaboration (though I hope some are!).

In Spring 2013, I was a third-year undergraduate at an impasse. A couple years prior, I had made the unusual decision to turn my back on Journalism in favor of pursuing a B.S. in Physics (despite my interest in science during high school starting and ending with Contact and Cosmos). Thanks to my wonderful undergraduate advisors (and their yearly program at Green Bank that biased me towards radio-frequency observing), I’d grown extremely fond of astronomy research; however, my lackluster course grades and test scores left me doubting whether I could actually become an astrophysicist. My decision to apply for the NSF Research Experiences for Undergraduates (REU) program at the Arecibo Observatory — and the unimaginably good luck I had in being offered the opportunity — changed the course of my career permanently.

"Jodie Foster" cabin from the movie Contact.

When I arrived in Arecibo that May, I fell immediately in love with the observatory. The telescope, nestled perfectly in the surrounding mountains, was beautiful and imposing in its engineering and aesthetics. I loved so many aspects of my time there: walking around and under the dish, listening to the Coquís as I fell asleep, climbing the approximately one million stairs to the “Jodie Foster” cabin where the girls slept, and traveling around the island in our spare time. I even loved the late nights of observing (which was good, because I had a lot more of those in my future). Most of all, I loved getting to know my fellow REU students — some from Puerto Rico, some from the mainland US — and spending time with the observatory’s many wonderful staff and scientists (and cats!).

I returned home at the end of the summer confident in my future as an astronomer  

Tattoo of the first MSP Dr. Cromartie
discovered.

My REU project acquainted me with millisecond pulsars (MSPs), a class of rapidly rotating neutron stars whose apparent “pulses” arrive at steady rates over long time spans. I was tasked with using the telescope to observe unidentified gamma-ray sources catalogued by the Fermi Large Area Telescope in order to discover new MSPs. With the tireless support of several advisors (whom I’m lucky enough to have as colleagues today), I discovered 11 new MSPs, six of which were in data we took that summer. Each new discovery was as exciting as it was validating; it made me feel as though I was really doing science. It was so exciting, in fact, that I got a tattoo of the first MSP I discovered (and no, I don’t regret it!). Being given the opportunity to do that research, and in a place as inspiring as Arecibo, is the reason I returned home at the end of the summer confident in my future as an astronomer.

With the support of both my undergraduate and REU advisors, I wound up at the University of Virginia for graduate school where I could pursue exactly what I wanted: studying MSPs with large radio telescopes, Arecibo included. My focus, both in graduate school and now as a postdoc, has been pulsar timing, which describes the process of creating a model to predict the time of arrival of every single one of a pulsar’s pulses over long time spans. At the beginning of graduate school I became involved in the NANOGrav collaboration, which harnesses pulsar timing in an effort to observe low-frequency gravitational waves from the coalescence of supermassive black hole binaries. I was grateful that my first NANOGrav meeting brought me back to Arecibo; being at the observatory reminded me of why I fell in love with astronomy — and pulsars specifically — in the first place. I was also grateful that frequently observing with Arecibo was so central to the success of NANOGrav science. Arecibo even played a pivotal role in my non-NANOGrav research during graduate school, some of which involved following up on Fermi MSPs that I had discovered during my REU.

The fate of Arecibo hung in the balance for much of my time in graduate school (though by no means for the first time in its long history). The constant auditing of the observatory’s financial requirements was frustrating to witness as someone who had the privilege to see Arecibo’s enormous scientific and educational impact up close. How could anyone doubt that the observatory, which had impacted the lives of so many scientists and students from both Puerto Rico and abroad, wasn’t worth the relatively meager cost of its continued operation?

I submitted a proposal in September for what would be the final deadline in the telescope’s history

Gregorian dome of Arecibo.

When we heard of the initial cable break in August and the increasingly worrisome reports that followed, I found myself reassessing Arecibo’s impact on my career to that point. I had defended my PhD a few months before, and was mere weeks away from beginning my postdoctoral fellowship. Without Arecibo, I’d undoubtedly be in a very different situation (perhaps I would have been more receptive to the voices — both internal and external — that told me a career in astrophysics wasn’t an achievable goal). When proposing my postdoctoral research activities, I was hoping to use Arecibo extensively; in fact, I submitted a proposal in September for what would be the final deadline in the telescope’s history. December brought the news of the telescope’s collapse, and I was heartbroken. I thought of the observatory’s staff and scientists, my colleagues who had used the telescope for decades, and the countless students who might otherwise have been inspired by some future visit to the observatory. I selfishly felt grief that I’d never see the telescope again, and worried about how my research would suffer in its absence.

The community that loved and relied on the observatory had shown remarkable resilience since the first cable break, but their determination after this disaster was awe-inspiring. Hundreds of scientists, engineers, teachers, students, and others banded together to honor the legacy of the telescope and plan for the observatory’s future. I think the speed with which the white paper was produced is a testament to Arecibo’s impact, and I think the dedication of those who worked hard to write it helped introduce a bit of optimism in the wake of a devastating loss. The observatory isn’t going anywhere; rather, we’ve been presented with the opportunity to add to its already impressive scientific legacy with a next-generation instrument. I hope that the astronomical community at large will take time to recognize the enormous impact that the telescope had over its nearly 60-year history, and that those in charge will be receptive to the innovative ideas being offered by the extraordinarily diverse group of people to whom the Arecibo Observatory is so important.