Astrophysics
For my research I use analytical calculations, numerical tools, and hydrodynamical simulation codes such as DISCO to address questions in black hole formation, binary evolution, and the role of astrophysical accretion disks. Much of my work is motivated by ongoing gravitational wave experiments LIGO/Virgo/KAGRA, which are unveiling the lower-end of the mass spectrum of black holes via detections of binary mergers, as well as future missions like the Laser Interferometer Space Antenna (LISA) which will detect the interactions of compact binaries and supermassive black holes across the Universe. My aim is to address what sources we will detect and how we can prepare to gain the most information from these detections. I am interested in the flow of gas around black holes, which we know is a critical process throughout the lifetime of supermassive black hole growth and for which a lot of puzzles remain to be answered.
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Star formation can occur in massive accretion disks in Active Galactic Nuclei, producing unique stellar populations which seed sources of gravitational waves, including extreme mass ratio inspirals. I've developed a comprehensive model of the formation of these sources, starting with solutions for the structure of accretion disks that become gravitationally unstable.
This work demonstrates the significance of this formation channel, quantifying how low-frequency gravitational wave sources born in accretion disks may constitute a substantial fraction of events detected by space-based detectors.
Due to their evolution in a gaseous environment, the orbital characteristics of these systems will be substantially different from similar events that form via dynamical interactions in dry nuclei. A primary focus of my work is to develop the framework to detect these sources and analyze their waveforms, especially because their detection will provide constraints on accretion disk environments which are spatially unresolvable to electromagnetic observations.
To start with the initial stage, I am working with Simona Pacuraru (University of Birmingham) alongside Noah Kubli and Lucio Mayer (University of Zurich) to model the first stages of fragmentation in an AGN disk. Simona has developed beautiful simulations using GIZMO-MFM that provide the initial mass of fragments (nascent protostars), their growth rates, and their orbital trajectories.
I am a core member of the LISA Consortium. Our white paper, recently published in Living Reviews in Relativity, outlines the capabilities of the LISA mission for driving astrophysical discoveries. You can also check out the official LISA Definition Study report — AKA the Red Book.
I coordinated one of the first Astro Working Group collaborative projects on a simulation comparison for black hole binary evolution in accretion disks. Not all simulations find the same results, so it is critical to compare our techniques to better understand the tools we use to predict the fate of this system: will the binary shrink to the scale where it becomes a powerful gravitational wave source? If so, what will its orbital properties be? Can the gas dynamics produce informative electromagnetic or gravitational wave signatures? Our results show that we need to be careful with how we model these systems, especially as we approach the regime of highly ionized, rapidly accreting massive black holes.
The evolution of supermassive black hole binaries in gas-rich environments is widely studied for both electromagnetic search campaigns and GW predictions. For binaries that coalesce in the LISA frequency band, interaction with surrounding gas can leave imprints on the waveform, as shown by Mudit Garg (NYU). Environmental interactions can also excite eccentricity in the binary, which, if measurable, can provide deeper insight into how massive black hole binaries form in their respective environments.
Gas-embedded black hole inspirals experience torques from their environment that are sensitive to poorly-constrained gas properties. With a suite of hydrodynamical simulations, I find that these torques can impart unique imprints in the gravitational waveforms, which presents an opportunity to probe accretion disks solely with gravitational waves.
Interaction with gas can be present in the waveforms of extreme or intermediate mass ratio inspirals as well as binaries of intermediate mass black holes (environmental effects are relevant for more than just EMRI sources!), demonstrated in recent works with Mudit Garg.
My simulation studies found that torques on embedded black holes can fluctuate on short timescales. This motivated a study with Lorenz Zwick (NBI) to calculate the effect of high frequency torque variability on disk-embedded binaries, which can produce multiharmonic and multiband GW emission. This is particularly relevant for EMRIs in turbulent accretion disks, or for more massive SMBH binaries surrounded by circumbinary disks.
The interaction of a binary with a surrounding gas disk leads to variable accretion and torques, which has critical implications for the evolution of supermassive black hole binaries during gas-driven hardening stages. A suite of simulations led by Paul Duffell (Purdue University) demonstrate how this torque is sensitive to the binary and disc parameters. These systems are prime candidates for electromagnetic signatures associated with GW emission — read our Astro2020 white paper.
Increasing evidence supports that shocks are ubiquitous in nova outflows and are responsible for powering nova emission across the electromagnetic spectrum. In this work I showed that these shocks can be radiative, producing regions in the ejecta that compress and cool rapidly, which creates prime sites for dust formation. This explains the puzzle of early dust formation in these violent eruptions — check out our Astro2020 white paper.
I enjoy speaking to a broad range of audiences (scientists and non-scientists alike) on topics ranging from gravitational waves to cool solar system missions — e.g. with Astronomy on Tap Nashville, Astronomy on Tap NYC, and the Columbia Astronomy Outreach program. I also care about participating in events that encourage youth involvement in science, such as "Meet the Scientist" at the Intrepid Museum's annual Kid's Week.
My teaching practice is motivated by inquiry-based methods. My strategy is to construct lesson plans that are accessible to various learning styles, so that students can engage with material in individual—and more effective—ways.
By learning science through doing science, we also develop the tools necessary to analyze and comprehend information both in the research lab and in our daily lives — asking questions, analyzing data, developing sound conclusions, acknowledging uncertainty, and communicating these aspects to others.
In addition to TAing and instructing lab courses as a graduate student, I participated in the Institute for Science and Engineering Educators Professional Development Program in 2015 and in 2016 as a Design Team Leader. In 2016, I received the Lead Teaching Fellowship at Columbia University, during which I attended several pedagogical workshops and organized a few specifically for the Astronomy Department.