RESEARCH
1. Black holes
- First BHs in the Early Universe
Reionization, Cosmic Dawn, X-ray sources, Population III star and its remant compact objects and X-ray binary. Formation and mergers of Population III compact object binaries.
- Supermassive Black Holes (SMBHs)
Formation and growth of SMBH, coevolution with galaxy and the feedback on intergalactic medium.
growth mechanism, tidal disruption, mergers and gravitational wave emission.
My Research Interests
2. Stellar Dynamics
Dynamics in stellar clusters and their formations.
3. Hot Jupiter
Evolution of atmospheres of hot Jupiters, shocks and turbulence in atmospheres, energy dissipation mechanism.
Recent Research
(up to the two most recent studies)
1. Turbulence-driven thermal and kinetic energy in the atmospheres of hot Jupiters (submitted to MNRAS, 2018)
A number of hot Jupiters are observed to have radii larger than what predicted from standard cooling models. The origin of the radius inflation is still debated. One idea to explain the inflated radii is injection/dissipation of heat via turbulence and shocks. In this study, my collaborator Michael Zingale, Rosalba Perna and I performed high resolution 3−dimensional compressible hydrodynamics simulations to investigate the effects of shocks and turbulence on energy transport into hot Jupiter atmospheres, under a variety of shear gradients. We focus on a local atmospheric region to accurately follow the small-scale structures of turbulence and shocks. We find that the effects of turbulence above and below a shear layer are different in scale and magnitude : local effects below the shear layer, but spatially and thermally large influences on almost the entire region above the shear layer. We also find that shock formation is local and transient. We infer that the time-averaged heat energy flux at P ∼ 1 bar is insignificant, on the order of 0.1% - 0.001% of the incoming stellar flux with a shear motion at P ≃ 1 mbar - 100 mbar. Our results suggest that it is more important how deep turbulence occurs in the atmosphere, than how unstable the atmosphere is for effective energy transfer.
2−dimensional slice plots showing the temperature for our two models, but with the shear layer at a deeper level, Psh = 100 mbar
2. Interactions between multiple supermassive black holes in galactic nuclei: a solution to the final parsec problem
(MNRAS, 2018)
One of the fundamental questions in Astrophysics whether supermassive black hole (SMBH) binaries would further decay and eventually merge (famously known as the "final parsec problem"). In this study, my collaborators, Rosalba Perna, Zoltan Haiman, Jeremiah Ostriker, Nicholas Stone, and I tackled this problem using N-body simulations. We model BH mergers with two extreme binary decay scenarios for the ‘hard binary’ stage: a full or an empty loss-cone. Our dynamical approach is the first attempt to study the dynamical evolution of multiple SMBHs in the host galaxies undergoing mergers with various mass ratios. We find that SMBH binaries are able to merge in both scenarios via multi-body interactions or dynamical friction. There is no “final parsec” problem in either scenario. Using the computed merger rates, we infer the stochastic gravitational wave background (GWB). See our paper for more details!