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In September 2022, I joined the Department of Astronomy & Astrophysics at the University of Toronto. For my thesis work, I study the evolution of stellar binaries in the centers of galaxies, and I'm advised by Drs. Yanqin Wu and Scott Tremaine (CITA, IAS). My past work has focused on the dynamics of planetary systems, and I'm interested in a broad range of astrophysical problems.
I'm passionate about developing my science communication skills and working with other academics to get the public excited about space! I'm part of a team of UofT students and postdocs developing coding-forward astronomy materials for high school students. I also wrote for Astrobites and served on their Education committee, and I helped lead UofT's monthly Astrotours lectures.
Please find my CV here. For science or outreach questions, please reach out to me at mark.dodici [at] astro.utoronto.ca.
M. Dodici, S. Tremaine, & Y. Wu (in prep). Check back in mid-2025, or let me know via email if you'd like a copy of the preprint.
Stellar binaries orbiting supermassive black holes are likely involved in a range of (often observable) astronomical processes. These processes, then, depend on the typical properties of this binary population. This population should be sculpted by a range of dynamical effects; each binary will be incessantly perturbed both by the supermassive black hole and the other stars in the dense cluster around it. This isn't a peaceful life!
In this work, we show that these effect will cause a surprisingly large fraction of the binaries in these environments to take on highly elliptical orbits, to the point that their closest approach during an orbit can be as small as a few stellar radii. At such small separations, in an extremely elliptical orbit, the two stars in the pair raise significant dynamical tides on each other. These tides rapidly shrink the binary orbit, leaving the pair separated by just a few times their own radii. We find that this "diffusive tidal shrinking" should act on roughly half of the binaries in the central few parsecs of the Milky Way, for example, and suggest that it should sculpt the binary population in the central part of any galaxy with a supermassive black hole.
As seen in M. Dodici & S. Tremaine (2024). Studying Binary Formation under Dynamical Friction Using Hill's Problem. The Astrophysical Journal, 972, 2, 193.
Start with two objects in space (stars, asteroids, black holes, whatever you like!) that are unbound from each other. If you throw them at each other, they will interact gravitationally. However, it's impossible for them to form a permanent binary pairing — they'll always move away from each other again after some amount of time — unless you have some way to get rid of energy. If you've got a lot of gas around, for example, energy can "dissipate" into the gas through gravitational interactions.
For the last few years, researchers have studied this process for stellar-mass black holes in the gaseous disks that sometimes crop up around supermassive black holes at the centers of galaxies. There should be a lot of solo stellar-mass black holes in these regions, and there's a lot of background gas in the disk, so perhaps you can form a lot of binary pairs with these stellar-mass black holes. If you form a lot of binaries, the conditions are also amenable for the black holes to spiral into each other and merge, inducing gravitational waves detectable by LIGO/Virgo.
But how easy is it to actually form a binary in this way? In this work, we take a simple approach to the problem of gas-driven pairings, and we introduce the idea that stars in the centers of galaxies can lead to binary formation in much the same way. We run over 100 million simulations of objects approaching each other under dissipative forces, covering a much wider range of this problem's vast parameter space than past works. We find simple relationships between the properties of the gas disk or surrounding stars and the efficacy of binary formation, and we compile recent results from other researchers to show that they've been finding the same relationships! We also point out that our understanding of these gas disks is really very uncertain, and that different models give hugely different rates of binary formation, which present problems for constraining this channel of LIGO/Virgo source formation.
Conveniently, everything about this work is scale-free, so the results can be applied to completely different scenarios – like the formation of binary asteroids in the gas disks of a nascent planetary system. Let me know if you have a good use-case!
I've served as a TA in astronomy courses for non-majors at both Princeton (~150 students) and Toronto (~1500 students). Through these courses, I've gained a wealth of experience in simplifying complex problems and getting people excited to dig into the messy details of astrophysics. More recently, I've been a TA for second- and third-year astronomy courses.
I've also spent a lot of time thinking about how I communicate science on a broader scale. During my Bachelor's, I won an award for a three-minute, general audience video explaining one of my junior-year independent research projects. I also worked for several years as a podcast and video editor for The Daily Princetonian, developing concision and clarity in my writing and building skills across the pipeline of multimedia production. As a graduate student, I've written for Astrobites, a blog of daily paper summaries geared toward undergraduates interested in science; I helped develop a series of workshops for high school students, introducing them to coding and astronomy through accessible, no-experience-necessary talks and activities; and I attended ComSciCon-CAN, a Canada-wide workshop for graduate students interested in improving their own science communication.
I received an A.B. with high honors in Astrophysical Sciences from Princeton University (May 2022). I also completed a certificate in Planets & Life. As part of the degree, I completed two independent research projects in my junior year and an undergraduate thesis (see Research section below for more on these projects). I focused largely on planets and planetary systems like our own, with a strong interest in astrobiology as my impetus for studying astronomy in general. As I completed my undergraduate thesis under Drs. Christopher Spalding and Jeremy Goodman and transitioned into graduate school, my interests began to shift to from planetary dynamics to dynamics as a whole.