James W. Johnson

Astrophysicist | Presidential Fellow | Software Developer



"To confine our attention to terrestrial matters would be to limit the human spirit."
-Stephen Hawking
Journal Publications
Seminars & Conference Presentations
The Big Bang produced only hydrogen, helium, and trace amounts of lithium. Everything else - from the carbon in our cells and the oxygen we breathe to the silicon in our computers and the iron in our infrastructure - was synthesized in stars through the nuclear reactions they facilitate. This is what Carl Sagan meant in his famous quote "We are made of star-stuff."

My research sits at the intersection of astrophysics and nuclear physics, seeking to understand which nuclear reactions occur when, where, and under what astrophysical conditions. By their very nature, the nuclear reactions powering stars and occurring in the wake of supernovae change the chemical composition of the material. This material is ultimately expelled as gas back to the host galaxy's interstellar medium, where it can be incorporated into the next generation of stars and planets that will condense out of the gas.

Being the sites of star formation and supernovae in the universe, galaxies are like petri dishes of their own nuclear reactions, retaining the nuclear products that come out of their own stars. By studying the present-day chemical content of the stars and gas within galaxies, we can learn about the history of nuclear reactions that gave it such a composition. This graphic, produced by my colleague and advisor Jennifer Johnson, illustrates which elements are produced by which astronomical phenomena and in what relative amounts.

The majority of this work sits in a field called Galactic Archaeology, which studies this very connection between a galaxy's evolutionary history and its present-day chemical composition with particular interest in our home galaxy - the Milky Way. Revolutionary big-data surveys such as APOGEE and GALAH have collected and continue to collect spectra for millions of stars, and by combining these spectra with models for stellar atmospheres, we can estimate their chemical compositions. Other surveys such as MaNGA collect similar data for external galaxies. By comparing galactic evolutionary models which track nuclear processes to data such as these, we can deepen our understanding of physics on both galactic and nuclear scales.

Links to my publications in peer-reviewed scientific journals can be found here.
Recently, I expanded my research efforts beyond galactic archaeology to the supernovae themselves. In this endeavor, I'm collaborating with Ohio State's revolutionary All Sky Automated Survey for Supernovae (ASAS-SN). In particular, I'm studying the thermonuclear detonations of white dwarf stars (type Ia supernovae) from a statistical perspective. These supernovae are known to produce much of the iron, nickel, and zinc in the universe, and are known to arise more frequently in low-mass, star-forming systems (e.g. Mannucci et al. 2005; Brown et al. 2019). The origin of this result is, however, something of a mystery: is it purely because of the different star formation histories of galaxies of different masses and morphologies? Or is it that low-mass galaxies are known to have low metal abundances (e.g. Andrews & Martini 2013) and the binary star systems - the progenitors of type Ia supernovae - are more abundant where metal abundances are low (Badenes et al. 2018; Moe, Kratter & Badenes 2019)? Stay tuned for the results!


"If you can't communicate and talk to other people and get across your idea, you're giving up your potential."
-Warren Buffet
Check out the slides from a few of my recent seminars and conference presentations!
I gave this talk at the 2021 SDSS Collaboration Meeting, held virtually. I gave a talk with similar content at the 2021 GALAH Science Meeting - check out the YouTube recording!
I gave this talk at the 2020 SDSS Collaboration Meeting, held virtually.
I gave this talk in the Inter[stellar+galactic] Medium Program of Studies Seminar at the University of California Santa Cruz Department of Astronomy in May of 2019.


"The way a team plays as a whole determines its success. You may have the greatest bunch of individual stars in the world, but if they don’t play together, the club won’t be worth a dime."
-Babe Ruth
James W. Johnson
David H. Weinberg
[Distinguished Univ. Prof., Ohio State]
Jennifer A. Johnson
[Assoc. Prof., Ohio State]
Charlie Conroy
[Prof. of Astronomy, Harvard University]
Fiorenzo Vincenzo
[Asst. Prof., Univ. of Hull]
Jonathan C. Bird
[VIDA Postdoctoral Fellow, Vanderbilt Univ.]
Emily J. Griffith
[Presidential Fellow, Ohio State]
Ryan J. Cooke
[Assoc. Prof., Durham Univ.]
Christopher S. Kochanek
[Professor, Ohio State]
Krzysztof Z. Stanek
[Professor, Ohio State]
John W. Bredall
[Graduate Student, Ohio state]
Liam O. Dubay
[Graduate Student, Ohio State]

Computational Tools

"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do."
-Ted Nelson
My research generally takes a theoretical perspective, relying heavily on high-efficiency calculations and numerical simulations. As a self-identified computer nerd with this motivation, a portion of my work entails developing new computational tools intended to deepen our understanding of the universe.

I have also incorporated my computational work into my teaching efforts by constructing a python bootcamp geared toward the typical computational skills of astronomers. Check it out!

Versatile Integrator for Chemical Evolution

VICE is an open-source galactic chemical evolution software. A python package with a backend written in C, VICE enjoys the powerful computing speeds of a compiled language while retaining the scientific flexibility and ease-of-use of python. Best described as a "one-size fits all" software library for this purpose, it can handle most chemical evolution models without any modifications to its source code.

Many evolutionary parameters typically built into these models (e.g. a galaxy's star formation history) are recognized by VICE as arbitrary, user-defined functions of time, allowing exploration of highly complex parameter spaces. In keeping with this model, VICE also allows users to declare their own nucleosynthetic yields directly, independent of previous studies in the literature; it will also calculate these yields upon request to assist in this process.

In March 2020, we published updates to VICE that extend its features to multi-zone chemical evolution models. In keeping with its model of flexibility, users may specify the mixing processes affecting both gas and stars in their models by telling it directly how much gas is moving between pairs of zones and which zone each individual stellar population is in at a given time. In this way, users can construct their own mixing processes for their models and let VICE handle the rest.


"The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires."
-William Arthur Ward
In May 2020, I designed, constructed, and administered a python bootcamp as the sole instructor. This consisted of six sessions, totaling ~20 hours of instruction and exercises aimed at astronomers with a background in functional programming. We focused on usage of a Unix Terminal, the tools provided by Anaconda, the standard contents of python documentation, multi-file python programs, and object-oriented programming up to and including inheritance and composition. In May 2021, I held this bootcamp a second time, and it was just as much of a success as the first one!

Although the participants thus far have mostly been undergraduate students beginning research, the target audience includes all researchers with a working knowledge of functional programming who are looking to take their python to the next level. In practice, this could be a scientist at any career stage - even a senior faculty member!

This event was hosted on GitHub. Slides, exercises, example code, and additional resources for those wishing to take their python programming to the next level can be found there.

Due to the Coronavirus pandemic, this event was held virtually. Check out the recordings!
I have also been heavily involved in undergraduate instruction at Ohio State. Over the course of my Ph.D., I served as a graduate teaching assistant for five sections of Astronomy 1101: From Planets to Cosmos across four semesters as well as one semester each of Astronomy 1142: Black Holes, Astronomy 1221: Astronomy Data Analysis, and Astronomy 1140: Planets and the Solar System.


"Space is for everybody. It's not for a few people in science or math, or for a select group of astronauts. That's our new frontier out there, and it's everybody's business to know about space."
-Christa McAuliffe
Having a life-long passion for outer space, I enjoy sharing my knowledge with others who share the fascination.

Since coming to Ohio State, I have been involved with the Friends of Ohio State Astronomy and Astrophysics (FOSAA) outreach effort. These events consist of a handful of Ohio State astrophysicists providing presentations on their area of research, followed by a lunch involving the same audience and many more of our colleagues. This affords the attendees the opportunity to discuss their unanswered questions about our place in the universe with our local experts.

As a German speaker, I was previously featured on Real Scientists DE, the German version of the Real Scientists blog. In addition to the blog entry itself, this involved a week of interacting with their followers on their twitter feed from June 15-21, 2020. This event was conducted entirely in German.

Additionally, I am a regular participant in Ohio State Astronomy's Diversity Journal Club, a recurring meeting within our department where we discuss issues diversity, equity, and inclusion in astronomy and astrophysics as a whole, but with particular attention to our own department and steps we can take to improve the current situation facing under-represented minorities.

About Me

"Astronomy compels the soul to look upward, and leads us from this world to another."
I am an astrophysicist in the 5th year of my Ph.D. at The Ohio State University Department of Astronomy.

I was born on May 4, 1995 in Iowa City, Iowa, but grew up and attended school in Lincoln, Nebraska, graduating from Lincoln East High School in May 2013. From there I moved to Nashville, Tennessee, where I earned my Bachelor's Degree in Physics & Astronomy from Vanderbilt University in May 2017. During my undergraduate I briefly lived in Berlin, Germany, studying the German Language and the history of Nazi Germany at the Freie Universität Berlin. After graduating from Vanderbilt, I moved to Columbus, Ohio in August 2017 to begin my graduate level studies at Ohio State.

Aside from astronomy, I enjoy petting dogs, traveling, playing the guitar, cooking, video games, stand-up comedy, and watching sports - particularly Football.

Contact Me

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