Research Highlights

The research areas mainly cover the following three topics, leading to the understanding of the structure formation and its feedback on various scales in the Universe:

1. Star and Planet Formation;
2. Galaxy Formation and Cosmology;
3. Energy Feedback and Interstellar Medium.

Star and Planet Formation

Our research efforts spreads from molecular cloud cores, processes of magnetized gravitational collapse, formation and evolution of protoplanetary disks, launching of magnetized centrifugal winds, star-disk interactions, jets and outflows, to evolution and dynamics of circumstellar and circumplanetary disks, disk-planet interactions, processes leading to the formation of planets, exoplanets and meteorites.

	Observational signatures of early disk formation by MHD models Exploring protostellar disk formation via misaligned rotation axes and magnetic field, and their observable features. The streamlines on the column density maps show the direction of flows along the picture frame. The black lines over Stokes Q and U parameters depict the direction of magnetic field estimated from the polarization angles. We predict that we witness magnetically directed spiraling behavior by polarization observations (Väisälä et al. 2019).(more on ASIAA site)
	Kinetic signatures in disks produced by multi-Jupiter-mass planets Moment-2 image for the 13C18O J = 3–2 transition of the fiducial model at face on. The location of the circumplanetary disk is labeled. A 4×10-3 stellar mass planet induces a prominent ring of high velocity dispersion inside the gap. This is the key planet-induced signature in this study (Dong, Liu, & Fung 2019). (more on ASIAA site)
	Planet migration in dusty protoplanetary disks Numerical simulation of low-mass planets migrating in dust-laden protoplanetary disks. The top panels show the perturbed gas and dust densities in the disk with initial metallicity 0.3 and particle Stokes number 0.06. The planet location is marked by the white cross. The bottom panel shows the orbital evolution of the two-Earth-mass planet. The planet migration behavior becomes chaotic after 200 orbits once numerous small-scale vortices formed in the vicinity of the planet.(Hsieh & Lin, 2020) (more on ASIAA site)
	Making planetesimals in turbulent disks is not easy The "streaming instability" (SI) in a physical protoplanetary disk model. (more on ASIAA site)
	Earth-sized planet formation around late M dwarfs Numerical simulations of the time evolution of orbital radii of protoplanets, i.e., their dynamical histories. The top panel is the case for protoplanets around a 1 solar mass star, and the bottom panel is that for a 0.056 solar mass star. Around low mass stars, protoplanets experienced more violent dynamical evolution, which even caused ejections of protoplanets. (Matsumoto, Gu, et al., 2020) (more on ASIAA site)
	Finding planets using Machine Learning A schematic diagram of the DPNNet (Disk Planet Neural Network) using a fully connected multi-layer perceptron. The first layer in yellow takes as input six feature variables observed from the protoplanetary disk. The output layer in red gives the planet mass as a target variable (Auddy & Lin,2020) (more on ASIAA site)
	Meteorites as a clue to the accretion in the Solar System Comparison between the numerical estimation of the rim thickness (hatched regions) and observed thicknesses of fine-grained rims (open circles) on the rim thickness and chondrule fraction plane. The dotted line is the analytical estimation for a simple case, and the dashed line is given by the dotted line with the observation bias. (Matsumoto et al., 2019) (more on ASIAA site)

Galaxy Formation and Cosmology

We are aiming at clarifying the multi-scale physics regarding the cosmological structure formation: large-scale effects of dark energy, spatial structures of dark matter distribution, galaxy formation and evolution, dust and chemical enrichment in galaxies, and stellar feedback through supernova explosions. We also predict observational signatures of first galaxies to reveal the origin of galaxies.

	Hydrodynamical evolution of supernovae and its effect on galaxy evolution How First Supernovae Altered Early Star Formation? The image shows the turbulent gas when a supernova collides with a nearby star-forming halo (Chen et al. 2017). (more on ASIAA site)
	Dust enrichment in a cosmic volume In the figure, we show the time evolution (at z = 6.1, 2.4, 1.0, and 0.0) of the projected density field of gas, small and large grains. The simulation box size is 50 h-1 Mpc (Aoyama et al. 2018). Based on this result, we are now calculating the statistical properties of dust emission at various redshifts. (more on ASIAA site)
	Dust properties predicted in a cosmological simulation We (Yu-Hsiu Huang, Hiroyuki Hirashita, et al.) modeled dust evolution in Milky Way-like galaxies by post-processing the IllustrisTNG cosmological hydrodynamical simulations in order to predict dust-to-gas ratios and grain size (more on ASIAA site)
	First galaxies Gas density distribution of the first galaxy after 33 Myr of evolution calculated by Chen & Chen. The gas and metals inside supernova remnants mixes with surrounding gas and other remnants and gradually collapses to the galaxy center. There are already over a thousand stars formed in the very central region. The star-forming region is tiny compared with the entire galaxy; thus, the stars are not shown here. (more on ASIAA site)
	Theoretical modeling of large-scale galaxy distribution for a test of cosmic acceleration The black solid line is the quadrupole moment of the galaxy power spectrum (the suppression of the power on small scales is due to virial motions of satellite galaxies) and the blue line is the reconstructed halo power spectrum after our method is applied. (Okumura et al, 2017) (more on ASIAA site)

Energy Feedback and Interstellar Medium

We are also aiming at revealing high-energy phenomena related to black holes and compact objects, since energy input (feedback) from these objects could affect the structure formation on various scales.

	World's First 3D Simulations Reveal the Physics of Superluminous Supernovae The nebula phase of the magnetar-powered super-luminous supernova from our 3D simulation. At the moment, the supernova ejecta has expanded to a size similar to the solar system. Large scale mixing appears at the outer and inner region of ejecta. The resulting light curves and spectra are sensitive to the mixing that depends on stellar structure and the physical properties of magnetar. (Ken Chen et al, 2020) (more on ASIAA site)
	Lightning black holes in dense molecular clouds (A) Side view of a BH magnetosphere. Photons are emitted from infrared to soft gamma-ray energies by the hot gas falling toward the BH in the equatorial, accretion (cyan) region. The soft gamma-rays collide each other to create electron-positron pairs in the polar funnel (white region). The created pairs are separated and accelerated into the opposite directions by the electric field $E_|| that is exerted along the magnetic field lines (in yellow-purple colored region). The outwardly accelerated electrons have ultra-relativistic energies to emit copious hard gamma-rays. (Hirotani et al.,2018) (more on ASIAA site)
	Evolution of grain size distribution in the interstellar medium Based on a one-zone evolution model of grain size distribution in a galaxy, we (Hirashita et al. 2020) calculated the evolution of infrared spectral energy distribution (SED), considering silicate, carbonaceous dust, and polycyclic aromatic hydrocarbons (PAHs). (Hirashita et al. 2020) (more on ASIAA site)