Meet the AAS Keynote Speakers: Prof. Brett McGuire

In this series of posts, we sit down with a few of the keynote speakers of the 243rd AAS meeting to learn more about them and their research. You can see a full schedule of their talks here, and read our other interviews here!

A photo of Brett McGuire taken from a 45 degree angle. He is a caucasian man with short, mildly dark brown har and is wearing glasses and a black collared button-up. He wears a white lanyard around his neck. In the background, the AAS logo is seen in a repeated pattern, blurred.
Professor Brett McGuire during the American Astronomical Society’s 228th meeting. Photo by Michael Owen Baker

Dr. Brett McGuire was sold on doing astrochemistry research ever since a professor at his undergraduate alma mater, the University of Illinois, summarized it as “I blow shit up, I hit it with lasers, and I look for it in space”. Decades later, this is still exactly what McGuire, now an Assistant Professor of Chemistry at MIT, is doing, harnessing the trifecta of state-of-the-art radio observations, laboratory techniques, and novel machine learning methods to hunt for new molecules in the depths of cold molecular clouds in our galaxy.

McGuire’s group has been focusing on looking for molecules called polycyclic aromatic hydrocarbons (PAHs for short) – honeycomb-shaped compounds composed of carbon rings containing anywhere from 10-25% of all the carbon in the universe! While on Earth PAHs are a considerable source of air pollution and cancer risk, in space PAHs are usually associated with star- and planet-forming regions and could be important catalysts for building the organic chemistry necessary for life. Surprisingly enough, McGuire’s group found PAHs hiding in an unexpected place: TMC-1, a cold dark molecular cloud core in the constellation of Taurus that is currently bereft of stars. Understanding the origin of PAHs in these clouds and their ramifications for interstellar chemistry and star formation are key research questions for the group: “We’ve been trying to delve into understanding why these molecules are there, how they got there, were they formed in situ? Are they inherited from prior generations of star formation? How do they affect the chemistry moving forward, and what other molecules are there?” says McGuire.

These molecular building blocks can be identified by their spectra – a unique chemical fingerprint of light that each molecule emits as it tumbles around in space. But the spectrum of even a single molecule is complex, carrying multiple emission lines of various strengths and wavelengths, and is also mixed in with lines from the other zoo of molecular species present inside a cloud. Trying to identify a single molecule in this sea of lines would be like looking at a  recording of a party and trying to pick out the sound waves of one person’s voice. In order to identify individual molecules and figure out what other species they should be looking for, McGuire and his group need a template – an image of what each molecule’s spectrum looks like in the lab – that they can match up with the spectra they observe using radio telescopes such as the Green Bank Observatory in West Virginia. These lab spectra are obtained by taking a gaseous molecule species of interest, such as a carbon ring, adding some nitrogen or oxygen, zapping it with a kilovolt lightning bolt, and seeing what is produced in the “resulting chemical miasma”. Though we don’t see rogue lightning storms raining through the cosmos, high energy UV and cosmic rays can bombard the atoms of the interstellar medium, similarly exciting the molecules present and causing them to react together to create the elusive molecular species McGuire and his group search for.

Since time on telescopes and in the lab is limited, McGuire’s postdocs and graduate students have been key in propelling another tool into the hunt to predict the abundance of molecules in a source: machine learning. “This is a really cool technique where you encode the structure of a molecule, so its chemical composition, how it’s bonded together, as ASCII text, as language. And then we use a natural language processing algorithm, so literally the same thing that you use for Siri, to interpret these ASCII strings as words and sentences, and learn the language of molecules.” McGuire can use the output of these models to predict what molecules to look for next, both in the lab and in space.

Despite being a cosmic molecule hunter, by training McGuire is a chemist, never having taken a single astronomy course. His first foray into astrochemical research was spurred by his father, a professor of chemistry, who encouraged him to get research experience as an undergraduate. While McGuire didn’t go into college intending to be a professor, he enjoyed doing research and realized that he liked taking the lead on projects and controlling their direction, something he would have the freedom to do if he kept going in academia. Nowadays, with his own research group, McGuire is passionate about supporting his students and mentees with the resources they need to do good science: “My students are incredible and getting to meet with them each week and have them come to me and say, “Here’s this really brilliant idea I had”, it’s just fantastic, right? That’s the best part of it now, is being able to just provide the tools and resources to these brilliant people, and having them tell me what they’ve done”.

With an impressive track record of molecular discoveries and many research threads keeping him busy, McGuire believes that having flexibility in working hours and a good work-life balance is key to sustaining productivity and happiness: “I can pinpoint the point in my scientific career where I started to become happy being a scientist, and that was part way through graduate school, I made the commitment that I would not do work at home. And that sounds really simple, but what it turned out to be was a separation between work, research, and life…I think that’s just really important to encourage folks not  to burn out, right, to make sure to set limits for yourself.” True to his word, when he’s not in the lab, McGuire transports himself to another world by being the dungeon master for a long-running D&D campaign or watching the British Baking Show. He also hosts a monthly podcast called Astrochem Coffee, where he interviews astrochemistry researchers, reviews current literature, dives into astrochemistry history, and reviews upcoming events and job opportunities.

If you want to learn more about finding, modeling, and understanding the “PAH Revolution”, tune into Prof. Brett McGuire’s Helen B. Warner Prize Lecture, currently scheduled for Monday, January 8, 2024 at 11:40 AM CT at #AAS243

Astrobite edited by: Archana Aravindan

Featured Image Credit: AAS

About Katya Gozman

Hi! I’m a third year PhD candidate at the University of Michigan. I’m originally from the Northwest suburbs of Chicago and did my undergrad at the University of Chicago. There, my research primarily focused on gravitational lensing and galaxies while also dabbling in machine learning and neural networks. Nowadays I’m working on galaxy mergers and stellar halos, currently studying the spiral galaxy M94. I love doing astronomy outreach and frequently volunteer with a STEAM education non-profit in Wisconsin called Geneva Lake Astrophysics and STEAM, as well as work at our on-campus observatory and planetarium.

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