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Titus Pankey and his groundbreaking supernova light curve.

Titus Pankey and his groundbreaking supernova light curve

23 October 2023

The creation of a Wikipedia article shines a spotlight on the long-unacknowledged physicist who was the first to infer the light-emission mechanism for type Ia supernovae.

Titus Pankey, writing, in 1964.
Titus Pankey in 1964. Credit: US Naval Research Laboratory/public domain

In 1962 Titus Pankey Jr made a discovery that would change the course of the study of supernovae. In his Howard University dissertation, Pankey argued that the electromagnetic emissions of certain supernovae are powered by nickel-56 decay. He then produced what today’s astronomers would recognize as the prototypical light curve of a type Ia supernova, the variety of stellar explosion that over the past quarter century has enabled precision measurements of the universe’s expansion rate.

Pankey—who was the first person to graduate with a PhD in physics from Howard and among the first 10 Black physics PhD holders in the US—would not be recognized for his work for decades to come. To this day, Pankey’s contribution remains drastically under-cited compared with the work of Stirling Colgate and Chester McKee, who independently introduced the same idea about 56Ni in a 1969 Astrophysical Journal paper.

There is also limited existing online material about Pankey’s life and legacy, and until last year there was no Wikipedia entry for him. As the former Wikipedian in residence at the Niels Bohr Library & Archives, one of us (Bell) researched and created pages for Black physicists, women physicists, and others who have been historically underrepresented in the field and on the site. (The library is part of the American Institute of Physics, which publishes Physics Today.) As one of the most visited sites on the internet, Wikipedia is a crucial place for centralized, accessible information; in our increasingly digital world, it is often the first landing spot for learning about a given topic.

Bell first came across Pankey’s name in an essay on the National Society of Black Physicists website that highlights Pankey and Arthur Thorpe as the first to receive physics PhDs from Howard. Although Bell found material about Thorpe in the Bohr library collections, she struggled to find information about Pankey.

With Pankey not only achieving a major first at one of the country’s preeminent historically Black universities but also the author of a breakthrough in supernovae, it was obvious that his story needed to be added to Wikipedia and made more accessible in the broader swaths of internet research. That story is a reminder of the gaps and omissions in what defines science and determines the scientific narratives that are remembered.

Who was Titus Pankey?

Born in 1925 in Hinton, West Virginia, Pankey grew up in Charlottesville, Virginia. As a young man he worked as a Pullman porter and later served in the US Army during the Korean War, according to his obituary in the Washington Post. After completing his tour of duty, Pankey enrolled at Howard, earned a bachelor’s degree in physics, and remained there for his graduate education.

Pankey had a successful career with the US Naval Research Laboratory and as a professor at Howard. He leaned toward experimental materials science, publishing widely on semiconductors and making contributions to the development of molecular beam epitaxy that are now well cited. His professional career was tragically cut short in 1979, when he suffered a brain injury during an assault and robbery that occurred in his home in Washington, DC. Despite this setback, he continued physics research at home until his death in 2003.

Titus Pankey works with laboratory equipment.
Titus Pankey works in the Naval Research Laboratory around 1964. Credit: US Naval Research Laboratory/public domain

Pankey’s most important contribution to astrophysics came in his dissertation, “Possible thermonuclear activities in natural terrestrial minerals.” At the time, the source of Earth’s geothermal energy was unexplained. Pankey’s research focused on characterizing materials and measuring the magnetic susceptibility of rocks to test the hypothesis that the very slow nuclear fusion of silicon-28 to nickel-56 in the planet’s interior was responsible. (Today we know Earth’s internal heat comes from the decay of heavy radioactive elements.)

In the context of studying the decay rates of various elements, Pankey noted that the shape of the light curves measured for type I supernovae (the subcategories type Ia and Ib wouldn’t be introduced until the 1980s) could be explained by the radioactive decay of nickel-56 to cobalt-56 and then iron-56. Pankey’s hand-drawn figure illustrating that process is the earliest example of a type Ia light curve drawn using the now-accepted theoretical mechanism, where the rapid decay of 56Ni to 56Co causes the light curve to rapidly drop during the first few weeks of the explosion and the slower 56Co-to-56Fe decay underlies the later, more gradual luminosity decline. In their 1969 paper, Colgate and McKee independently introduced the same idea and, by using more detailed hydrodynamic and radiation transport calculations than did Pankey, demonstrated that the emitted light must be powered by the 56Ni decay chain.

A graph showing a quick rise in supernova luminosity followed by a steep dip over the course of 100 days.
In his dissertation, Titus Pankey charted the luminosity of a supernova explosion that was powered by the decay of nickel to cobalt to iron. Credit: T. Pankey Jr, Howard University dissertation, 1961; image courtesy of the Howard University Graduate School

Pankey’s supernova discovery is significant on multiple fronts, says Or Graur, an astrophysicist at the University of Portsmouth, UK, who referenced Pankey in his 2022 book, Supernova. Most of the light seen from type Ia supernovae is produced by the 56Ni decay chain, and the curve shows that iron-group elements including nickel and cobalt are synthesized during the explosion. Additionally, the luminosity of the supernova is set by the amount of radioactive nickel produced in the explosion, which enables astronomers to use the stellar explosions as standard candles. The ability to measure the distances to galaxies containing type Ia supernovae was essential for the researchers who in the late 1990s demonstrated that the universe’s expansion is accelerating. One can trace a direct line from Pankey’s idea to that Nobel Prize–winning research.

Bringing Pankey’s story to Wikipedia

Pankey’s work clearly meets the criteria for a Wikipedia page. Wikipedia is deeply imperfect in its representation of people who are not white men, however, in both science subjects and in articles more broadly. Donna Strickland, for example, did not have a Wikipedia page when she was awarded the 2018 physics Nobel; the site’s editors had previously rejected articles about her because they asserted she did not meet notability requirements. Strickland’s case has been described as both a metaphor for broader issues within Wikipedia and a clarion call for more thoughtful editing and considerations of prominence.

The Washington Post obituary was a major secondary resource in detailing aspects of Pankey’s life. Pankey’s name also came up in searches in multiple digitized archival newspapers, which provided snapshots of various stages of his career and revealed new details about his time at Howard. That information fleshed out the component parts of a typical biographical Wikipedia page, including “Early life,” “Education,” and “Personal life.”

Top portion of Titus Pankey's Wikipedia page.
The top portion of the Wikipedia article on Titus Pankey.

An important component of Pankey’s Wikipedia page is the link to his thesis, which includes the groundbreaking hand-drawn light curve, on ProQuest’s dissertations database. Although ProQuest is accessible only with certain institutional accounts, it is lucky that the thesis is digitized at all, as many documents from the pre-digital age are not readily available online.

Bell submitted Pankey’s Wikipedia page as a draft in June 2022, using a Wikipedia template that allows for peer review. (See the box below on how to create Wikipedia articles.) It was accepted quickly, with no debate over notability. Information about Pankey’s thesis and subsequent research was bolstered by an anonymous editor who filled in some of the technical gaps. That editor turned out to be the other author of this article, Caplan, who had been concurrently conducting research about Pankey’s life and work.

Tracing the citation path

The Colgate and McKee paper has more than 400 citations, according to the SAO/NASA Astrophysics Data System, whereas Pankey’s has 53. How did Pankey’s unquestionably important discovery get lost in the academic void?

One likely factor was its lack of visibility in the literature. Pankey’s thesis was published in a 1962 index of Dissertation Abstracts, to which doctoral students could submit summaries of their work to be distributed in compendium to other universities. His abstract appears on page 1395, among hundreds of other entries. A researcher who wanted a copy of Pankey’s thesis would have had to pay $2.75 to receive it on microfilm or $3.00 for a photocopy. An abstract of Pankey’s work was also published in a 1963 volume of Nuclear Science Abstracts. It was easy for the thesis to go unnoticed by the astrophysics community. The paper by Colgate and McKee, however, appeared in the popular Astrophysical Journal. Published in August 1969, the study received its first citation before the end of the year.

Notably, Colgate and McKee were both white physicists affiliated with predominantly white institutions. In a study published earlier this year, researchers using a data set of more than a million recent scientific papers found that nonwhite researchers are significantly underrepresented on editorial boards, face longer publishing times, and are less likely to be cited than their white colleagues. Across multiple fields and publishers, Black scientists are the least-cited group in the US. The citation gap is concerning and a testament to the persistent disparities in how the work of Black scientists is recognized.

Chanda Prescod-Weinstein, a physicist who last year released the Cite Black Women+ in Physics and Astronomy Bibliography (a Zotero library) to address citation gaps faced by Black women in those fields, points to the issue of epistemological marginalization in the context of Pankey’s work going uncited for so long. The question of race, resource allocation, and patterns of intellectual recognition all shaped how Pankey and his work were treated and affected science in an immediate, temporal way, she says.

Ronald Mickens, who has spent much of his career documenting and preserving information about Black physicists, says that Pankey likely never joined any research community around supernova studies and so did not have access to the informal “invisible colleges” that could have supported his work. He adds that Pankey did not advise any graduate students during his professorship, which may have also limited the reach of his work.

Pankey’s thesis largely disappeared from scientific discourse until 1980, when it was referenced in a paper written by Pankey himself. Published in Publications of the Astronomical Society of the Pacific, “Anomalous beta decay in type-I supernovae” begins with this passage:

Two decades ago (Pankey 1962, 1963), it was suggested that during type-I supernova eruptions a resonant fusion of two Si28 nuclei, followed by the beta decay of Ni56 and Co56 to Fe56, would explain the characteristic features of the luminosity curve. … More recently, a new theory, widely known as silicon burning (Bodansky, Clayton, and Fowler 1968) has been extended to type-I supernovae (Colgate and McKee 1969).

Although Pankey’s 1980 article did not have much of a citation impact, J. Craig Wheeler at the University of Texas at Austin cited Pankey the following year in his review article on the origin of supernovae. The article set off a minimal increase in recognition of Pankey’s work, with about one citation of the thesis per year throughout the 1980s and 1990s. Early citations appeared in papers by Virginia Trimble, Stan Woosley, and then graduate student Tim Axelrod.

Rectifying past omissions

Wheeler and Woosley say they don’t remember how they became aware of Pankey’s work. Speculating on reasons why Pankey’s contribution may have been overlooked, Woosley mentions the difficulty of broad literature searches in the pre-digital era, the possibility that Pankey’s work was classified as nuclear physics rather than astrophysics, and the way researchers receive credit for original insights. “It has been my experience many times—often on the receiving end of the neglect—that it is the people who develop, apply, and popularize ideas who often get the credit for [a] discovery even if they did not state the idea for the first time,” Woosley comments via email. “I don’t think this is necessarily a bad thing and certainly not sinister. On the other hand, original thought should be recognized when known about or uncovered later.”

Wheeler, author of that first paper to cite Pankey, expresses some regret about the limited early recognition of Pankey in the scientific community: “Looking back on it, I’m chagrined by this. … We could have done a lot more than just cited him. Invited him to meetings, reached out. One thing that is not uncommon is to invite someone to a meeting and [have them] give the after-dinner talk. That would have been a fascinating thing to do.”

A graph showing a quick rise followed by a drop over the course of more than 300 days.
Figure III of Titus Pankey's dissertation superimposed his theorized curve with type I supernova observations (circled dots) reported by astronomer Walter Baade. Credit: T. Pankey Jr, Howard University dissertation, 1961; image courtesy of the Howard University Graduate School

Today scholars such as Graur have come to learn about Pankey’s work from social media. More than a quarter of the citations of Pankey’s thesis are from the last three years, with 17 papers citing his work since 2020.

As in science, history must be updated when new information becomes available. The fact that Pankey’s work was unrecognized in the 1960s is not an excuse for ignoring it now. Colgate and McKee enjoy a legacy of influence and impact. Pankey deserves a legacy of priority: The mere existence of his work demonstrates how much earlier such insights on supernovae were possible.

For those reading this who are practicing astrophysicists, you have an easy task. When citing the formative work on type Ia supernovae, simply cite both papers. History is a story we tell ourselves about the origins of our community and profession. Let’s choose to make Titus Pankey part of that story.

Camryn Bell was Wikipedian in residence at the Niels Bohr Library & Archives of the American Institute of Physics from 2022 until earlier this year. Matt Caplan is a professor of physics at Illinois State University.

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