Things in Disks Yo NYC
Current Research
Hydrodynamic Modeling of Disk Torques
Hydrodynamic simulations of interactions between a gas disk and an orbiting object (like a stellar origin black hole) enable us to understand how such objects will move through a disk--including whether migration torques will push objects inwards or outwards, and wakes of multiple objects may interact.
Analytic Models of Disk Capture
Objects orbiting in a quiescent nuclear star cluster will interact with a newly arrived AGN disk. Our group explores the consequences of these interactions through analytic and semi-analytic models for the orbital evolution of both stars and stellar origin black holes which interact with an AGN disk.
Monte-Carlo Models
Models of the AGN channel for GW detectable binary black hole (BBH) mergers span a wide variety of astrophysical processes. Simultaneous modeling of all processes from first principles is computationally prohibitively expensive, so we use smaller scale simulations of individual processes to create approximate subgrid models for each of them, and then implement a large scale Monte Carlo model to obtain expected distributions of BBH properties, under varying assumptions for each process. We are currently working to create a public, user-friendly set of these simulations so that any astrophysicist can 'roll their own' models of the AGN channel!
Stars, Supernovae & TDEs
Stars embedded in AGN disks will evolve differently than those in a vacuum, and indeed, the growth and evolution of embedded stars may change the nature of the disk itself. We work on understanding the observable consequences of these newly theorized and exciting stars.
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​In addition, the dynamical interactions inside AGN disks may produce stars on highly eccentric orbits, which can become tidal disruption events. Though TDEs have long been observed in normal galaxies, their possible presence in active galaxies has only recently been considered. We are involved in both models of and observational searches for these powerful events.
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Electromagnetic counterparts to gravitational wave events could occur in AGN disks from the interactions of post-merger black holes with the dense gas in the disk. A major potential confounding possibility is supernovae occurring in the AGN disk, so we are pursuing models of such supernovae to allow observational distinction of the two processes.
Time Domain Analysis
AGN are inherently variable objects across short and long timescales, and across multiple wavebands. Sources of variability include those intrinsic to gas processes in the disk, as well as 'extrinsic' variability due to objects in the disk (e.g. supernovae, TDEs, BBH mergers, disk-crossing orbiters) and outside the disk (e.g. microlensing, transits, changes to the line of sight absorption). We are working to identify the causes of observed variability through observational analysis (including machine learning (ML) techniques), and using phenomenological and theoretical frameworks.
Observations of AGN at High Contrast
AGN are extremely bright but also extremely small in angular size. The material that supplies the accretion disk, and the galaxy that the AGN lives inside are often lost in the glare of the 'central engine'. Using observational techniques originally designed to detect planets hidden in the glare of their parent star, our group will be able to reveal the environment that surrounds AGN, and this will let us study both the cause of these vast accretion disks, and the effects they have on their parent galaxy.
Gravitational Waves & Multimessenger Astrophysics
Astronomers have long relied on light (or electromagnetic---EM---waves) to learn about our universe. It is still the 'messenger' we rely on most to understand the distant universe. However, binary black hole mergers of stellar origin black holes emit gravitational waves, which we are currently able to detect using LIGO/Virgo/KAGRA. GW represent a new 'messenger'! More massive black hole binaries are will also be detectable in the future, using the European Space Agency's LISA mission, and using pulsar timing arrays such as NANOgrav.
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By combining information from multiple messengers (possibly also neutrinos and cosmic rays) we can learn more about some of the most energetic events in our universe. If binary black holes merge in AGN disks, it is possible we will be able to both 'see' the mergers using light, and 'hear' them using GW, creating a powerful tool to understand these awe-inspiring events.
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