Prof. Duffell's field of research is broadly in numerical gas dynamics and magnetohydrodynamics (MHD). He has developed several unique and powerful numerical codes for solving the MHD equations using a novel "moving mesh" technique. These methods are advantageous for evolving highly supersonic and relativistic flows, which are quite common in astrophysics.
Our group's general process is to develop and write new numerical methods for evolving astrophysical flows, and to apply these codes to a wide variety of problems in astrophysics. Prof. Duffell has experience in planet-disk and binary-disk interactions, supernovae, gamma-ray bursts, hydrodynamic instabilities and turbulence, binary black hole and neutron star mergers, and active galactic nuclei. Because our group specializes in hydrodynamics rather than a particular astrophysical phenomenon, we have the luxury of working on a wide variety of topics.
Soham Mandal has experience in active galactic nuclei, both from an observational and theoretical perspective. He has developed a method for measuring how relativistic an AGN jet is propagating, and relating it to the observed morphology of the jet. His model proposes a criterion for whether a jet will be observed as a FRI or FRII object. Additionally, he has shown that the number and spacing of recollimation shocks in a jet can be related to the velocity of the jet head.
Presently, Soham is studying Rayleigh-Taylor instability in supernovae, to determine whether the morphology of a supernova remnant contains structural information telling us how much asymmetry the initial explosion started with.
Soham has developed his own unique code, SPROUT, for computing the evolution of expanding 3D flows over large dynamic ranges. Code paper is being written presently.
Publications by Soham:
Numerical Investigation of Dynamical and Morphological Trends in Relativistic Jets
Mandal, Duffell, and Li, 2022, ApJ Accepted
TXS 0128+554: A Young Gamma-Ray-emitting Active Galactic Nucleus with Episodic Jet Activity
Lister et al., 2020, The Astrophysical Journal
Ranadeep Dastidar is presently developing an NLTE synchrotron emissivity code for computing off-axis light curves relevant to multi-messenger GRB afterglows. For the hydrodynamic component, he uses the JET code, a highly adaptive moving-mesh code for relativistic radially-propagating multidimensional outflows. In order to determine the afterglow light curve, he first computes the hydrodynamical evolution of a highly relativistic flow (with arbitrarily specifiable initial conditions) to compare with afterglows of short and long GRBs, especially the afterglow from GRB170817A, the first confirmed neutron star merger detected by LIGO.
Danielle Dickinson is an observer working in the time-domain astronomy group at Purdue. She is interested in transients of all kinds, especially supernovae. Although she is an observer, she is doing theoretical work in our group, investigating the possible origins of FBOTs (fast blue optical transients) using hydrodynamical models.
Dillon Hasenour is developing a novel numerical method for nuclear hydrodynamics using a moving mesh. The idea is to combine a nuclear reaction network with a moving-mesh hydrodynamics code (developed by Hasenour) to evolve explosive astrophysical outflows. Hasenour has already demonstrated dramatic improvement in evolving nuclear-powered shockwaves where the nuclear binding energy is comparable to the kinetic energy in the flow.
How do we relate these computed hydrodynamical outflows to what we actually see? We talk to Dr. Jennifer Barnes, a postdoctoral researcher at the Kavli Institute for Theoretical Physics in Santa Barbara, Califonia. Barnes is an expert in radiative transfer, using the Sedona code to compute the evolution of photons as they propagate through an explosive outflow such as a supernova or kilonova. This can be a very complex calculation, which can hinge upon computing the opacities of high-Z elements, especially aborption and scattering from the many possible line transitions in the Lanthanide series. Dr. Barnes was among the group of researchers who correctly predicted the spectrum of a kilonova, before it was first detected in 2017.
Daniel D'Orazio is an Assistant Professor in the Niels Bohr International Academy, at the University of Copenhagen in Denmark. D'Orazio is the longest-running user of the DISCO code (other than Duffell himself) and has extensive experience in the field of supermassive black hole binaries. In particular, D'Orazio has experience relating observed AGN signatures to binary accretion and lensing models. He has also made predictions for the evolution of the orbit of a binary interacting with a disk, which we hope to compare wth future PTA detections of the gravtiational wave background produced by supermassive black hole mergers.
Yuan Li is an assistant professor at the University of North Texas in Dallas. Professor Li uses computer simulations to study various physical processes related to galaxy evolution and supermassive black holes. She has been an instrumental collaborator, assisting us to connect our idealized AGN jet models to physical observables.
Dr. Abigail Polin is a research scientist with a joint appointment at the California Institute of Technology and Carnegie Observatories. Dr. Polin studies supernovae, working on the boundary between theory and observations, building hydrodynamical models for supernovae and comparing them to observational data. One of her most prominent results was a prediction of the light curve and spectrum of what later became known as "2018byg-like" supernovae, Type-Ia supervovae that explode below the Chandrasekhar mass. Presently Dr. Polin is collaborating with us to build forensic tools for observers to describe the structure at various angular scales in supernova remnants.
Dr. Geoff Ryan is a postdoctoral researcher at the Perimeter Institute in Ontario, Canada. Ryan is (so far) the only code developer that Duffell has ever allowed to modify the public versions of his code. Ryan has implemented general relativistic magnetohydrodynamics (GRMHD) into the DISCO code, and continues to make major developments to improve code performance.
Ryan has experience working on binary-disk interactions, and GRB afterglows.