In this series of posts, we sit down with a few of the keynote speakers of the 246th 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!
Today, I had the wonderful opportunity to have a conversation with Dr. Susan Clark, a faculty member at Stanford University. She is the recipient of the Helen B. Warner Prize and will be giving the Helen B. Warner Prize Lecture at the AAS conference on June 9th, 2025 at 11:40 am! Dr. Clark focuses primarily on trying to understand the interstellar material of the galaxy. She will tell us all about this at her lecture “Magnetism and Morphology: Decoding the Interstellar Medium”.
A Dusty Galaxy
Our galaxy is FILLED with gas and dust. It can be tempting to think of each galaxy as a collection of stars, with each star having some planets going around it, and perhaps a central supermassive black hole that all the stars slowly dance around. However, it’s important to remember that all of these stars live in a sea of gas and dust that they constantly interact with, which is called the interstellar material, or the “ISM”.
The ISM varies over a huge range of temperatures and densities, meaning that it can be found in many different states of matter throughout the galaxy. Stars are formed out of this interstellar material, and when stars die they return material back to the ISM, enriched with whatever nucleosynthesis happened in the star during its lifetime. Key unknowns in this field are the interplay between the ISM and stellar evolution over the lifetime of a galaxy, how the different phases of the ISM interface with each other, and how all of this happens within the galactic magnetic field.
Magnetic Dust
Dr. Clark’s group focuses on mapping the distribution of dust and the magnetic field strength in the ISM. I wanted to highlight one specific method they use to detect the magnetic field, because it is so clever!
Dr. Clark has been particularly interested in producing three-dimensional maps of dust using polarization of background light. We can map the dust in two dimensions (up/down and sideways) just by looking at it along different lines of sight. Is it possible to also know how the dust changes towards/away from us? As an example, let’s assume Dr. Clark is trying to determine the dust density and magnetic field strength along one particular line of sight that happens to point toward a specific star. Light from that star is initially unpolarized. As the light travels through the ISM, it will interact with the dust particles and become partially polarized (because the dust will absorb light polarized in the direction of the dust’s magnetic dipole). By measuring how strongly polarized the light is in that direction, Dr. Clark can determine the orientation of the ISM magnetic field in the direction of that star. The key point here is that because all of this absorption must happen between the star and the Earth, this method allows one to constrain the third spatial dimension. By making this observation to many nearby stars whose distances are known, we can create a three-dimensional map of the ISM magnetic field! Dr. Clark recognizes that this is actually a data-rich field, where observations taken from other surveys, such as polarization observations of the cosmic microwave background can be used to answer unknowns in this field.. Therefore, ISM observations is the rare field of observational astronomy where the limiting step is actually trying to figure out what physics can be learned from that plethora of data already present, rather than what new surveys are necessary to understand the ISM better. On this note of using existing data in innovative ways, Dr. Clark has been instrumental in starting the Center for Decoding the Universe. The center aims to connect data scientists with astronomers and physicists to understand how much more can be learned from the large already existing multimodal datasets from observations of the universe.
A True Love for Learning
Whenever I get the chance, I like to ask scientists this question: “What do you think is the scientific purpose of doing fundamental research? Beyond the science we need to do to build bigger houses or live more lavish lives, is there a pure purpose for science?”
Dr. Clark sees learning and trying to understand the universe as core to being human. She sees the fact that we are curious and wonder about things as something that connects us to each other and makes life worth living in a fundamental way. Dr. Clark also emphasized that she wants this learning to be accessible to everyone. That access to quality education and the ability to learn—to be able to chase down the scientific answer to things that we wonder about—is a human right. She believes her job as a scientist is both to wonder and explore things, but also to build pathways that let anyone access this ability.
I would very strongly recommend tuning in to listen to Dr. Susan Clark’s lecture about mapping the interstellar medium Monday, June 9 at 11:40 am (Alaska time) at AAS246!
Edited by: Margaret Verrico
Featured Image Credit: AAS
