Research
My main focus is on the coupling of live radiative transfer in Smoothed Particle Hydrodynamics (SPH) simulations. Previously I have also worked on synthetic observations of 3D simulations of molecular clouds, doing a convergence study on the Xco factor and Nco.
Code development
I am a contributor to the smoothed particle hydrodynamics and magnetohydrodynamics code Phantom (publicly available via its repository) as well as the Monte Carlo radiative transfer code Mcfost (now publicly available in the repository).
On the rise times in FU Orionis events
In 1936, an unremarkable star in the constellation of Orion, FU Ori, suddenly changed brightness by 6 magnitudes over the course of a year, remaining bright ever since. The phenomenon has since been observed in a number of outbursting young stars, which have been classed as FU Orionis objects. There has not been an explanation before as to the cause of this sudden outburst.
Through the use of Phantom coupled with Mcfost, we created stellar flyby simulations and discovered that a disc penetrating stellar flyby results in the fast rise in the mass accretion rate.
Flyby scenarios had previously been discounted due to the long time it takes for disturbances in the disc to propagate to the main star. Our simulations find the fast rise time associated with FU Orionis events with the perturber going into outburst. This happens as the perturber captures the material from the disc while passing through. The perturber going into outburst is in line with observations from FU Ori, where the lower mass star is the brighter source in the binary star system.
Links to related media articles:
Monash press release: Astronomers find clue to solar system formation through well-known star by Silvia Dropulich
Universetoday: Astronomers see a star crash through the planetary disk of another star by Evan Gough
Syfy Wire article: Star trespassing on another star’s territory might tell us what happened in the early solar system by Elizabeth Rayne
Sciencenews article: Two stars’ close encounter may explain a cosmic flare that has barely faded by Ken Croswell
Sustained FU Orionis-type outbursts from colliding discs in stellar flybys
We perform 3D hydrodynamics simulations of disc-disc stellar flybys with on-the-fly Monte Carlo radiative transfer. We show that pre-existing circumstellar discs around both stars result in fast rising (~yrs) outbursts lasting 2–5 times longer than for a star-disc flyby. The perturber always goes into outburst with the accretation rate exceeding 10^-5 solar mass/year. Whereas we find that the primary goes into a decades long outburst only when the flyby is retrograde to the circumprimary disc rotation. High accretion rates during the outburst are triggered by angular momentum cancellation in misaligned material generated by the encounter. A large fraction of accreted material is alien.
Synthetic CO emission and the Xco factor of young molecular clouds: a convergence study
We performed synthetic observations on data from the SILCC-Zoom ins (SImulating the LifeCycle of molecular Clouds, Zoom-ins) using the Monte Carlo radiative transfer code radmc-3d (available in this repository). The zoom-ins had resolutions between 3.9 to 0.06 pc. With the synthetic emission maps we analysed the convergence of the CO emission and the Xco factor, finding that both are not yet converged at the highest resolution of 0.06 pc. Furthermore, we also found that the Xco factor from the synthetic observations of the observable region is below the commonly assumed value for the Milky Way.