ASTROPHYSICS & COSMOLOGY
Our research themes include theoretical studies and cosmology covering the whole of astrophysics.
We’ve been conducting not only the study for the identity of Dark Matter which is the mysterious matter of the Universe for long, but also the study for the formation principle of Large-scale structure of the Universe. Also we actively have engaged to develop the personal brand algorithm investigating the structure of the Universe. For now, the algorithm has shown a great performance as a result of a test by ourselves, which is comparable with the well-known friends-of-friends (FoF) algorithm.
Using our strong computing resource being proud of the Computational Science Research Center, we activate the cosmological simulations (N-body, Hydro-dynamic etc..) by ourselves and conduct cutting-edge analysis like Machine & Deep Learning.
1. Large-scale Structure of the Universe
Large-scale structure studies have two strands: observationally we want to try to measure the statistical properties of the actual distribution, as a function of cosmic epoch, and to try to infer the distributions of both ordinary baryonic matter and dark matter. Tools to do this include galaxy clustering studies, measurements of the velocities of galaxies as they fall towards overdense regions and measurements of the fluctuations in mass with position afforded by gravitational lensing studies. Experiments such as the upcoming Euclid mission aim to carry out new, accurate measurements of some of these observables. A key component of our work is to link these measurements of the relatively recent Universe to the much lower amplitude structures we can observe in the earlier Universe via the cosmic microwave background.
More details, we have studied the evolutionary process of galaxies nearby filament structures on the phase space by using cosmological N-body simulation data. Vice versa, to understand and analyze the principle of large-scale structures itself, we look through galaxies and super-cluster data. In this context, we are developing a brand-new algorithm, called Mulguisin, to demonstrate the large-scale structure with statistical and quantitative data. For now, It has already been approved for its remarkable performance which is comparable with the other famous algorithms like friends-of-friends (FoF) algorithm and so on.
2. Early Universe
Our Early Universe studies span the cosmic epochs from the Cosmic Microwave Background (CMB) radiation representing the recombination epoch to the Epoch of the Reionization (EoR) indicating the period for the state of all hydrogen atoms from being neutral to entirely ionized.
But, since the observational efforts to detect the Early Universe is still challenging, we mostly make use of (semi-) numerical simulations and then try to analyze the childhood of the Universe based on the generated dataset. Thanks to the powerful computing resource we have, we can easily overcome the process for simulating the epochs. Using cutting-edge analytics, we can also actively do research without obstacles for computational capabilities for the most part. Recently, for the epoch of reionization, we ran the 21cmFAST semi-numerical simulation and generated 21cm differential brightness temperature image maps, which allows to track the process of re-ionizing evolution based on the cosmological model we assumed. Then using the linear regression analytics applying to Deep Learning, so to speak “Deep Neural Network with Convolutional methods”, we have successfully built our neural network model with a great accuracy and demonstrated the new way to get over the hurdles for observational challenges.
For our cosmology studies, we have been doing research about the core of cosmology. We are calculating and modeling the physics of the cosmos. Current research in theoretical astrophysics and cosmology at our Computational Science Research Center explores a wide range of critical questions. Major topics include numerical simulations of the Dark Matter based on a variety of cosmological models, gravitational lensing. By using our physical and intellectual resources, we can afford to verify some parts of the validity of the model through simulating the process and solving it in a theoretical way. For example, one of our studies is that measurement of offsets between the Dark Matter particles and stars which came out from N-body simulation based on the scalar Fuzzy Dark Matter model, not Lambda Cold Dark Matter. On this way, our cosmology research team is always eager to the truth of the Universe, and of nature by questioning the fundamental and basic ideas we have been trusted so far.
4. Experimental High-Energy Astrophysics
Cosmic rays are charged particles. We believe they are accelerated in tremendous astrophysical explosions such as supernovae, gamma-ray bursts, and the turbulent regions of space near supermassive black holes. By studying cosmic rays, we hope to gain a better understanding of these violent (and ubiquitous) objects.
High-energy gamma-ray observations are an essential tool in the study of the origins of cosmic rays, because gamma rays are created when cosmic rays interact with material near their acceleration sites. Because they are electrically neutral, the gamma rays produced in such interactions are not perturbed by the magnetic fields which fill our own galaxy and intergalactic space. Therefore, we can use them to perform gamma-ray astronomy.
By observing the spatial distribution and intensity of gamma rays across the sky, we can attempt to identify the locations of cosmic ray accelerators. In addition, the time variability and energy spectra of the gamma-ray emission can be used to study the environment of the accelerators and the mechanisms of charged-particle acceleration. The highest-energy gamma rays (above 1 TeV) and the shortest timescales of variability provide important constraints on the mechanisms at work in acceleration sites.
For gamma-ray physics, cosmic-ray air showers are the source of a large background that is only removed with some difficulty. However, at TeV energies the cosmic rays are themselves a fascinating topic for study. Since 2007, several gamma-ray observatories located in the northern hemisphere (including Milagro) have reported anisotropy in the arrival directions of the cosmic rays around 10 TeV. Although the anisotropy is quite small, with an amplitude of a few parts per thousand, its presence is still surprising, because it is expected that galactic magnetic fields should completely randomize the arrival directions of cosmic rays in this energy range.In 2011, cosmic ray measurements from the IceCube Neutrino Observatory demonstrated the extension of the anisotropy to the southern hemisphere. The origin of these features — a nearby supernova remnant? heliospheric effects? magnetic lensing? — are not known. The HAWC Observatory, which has a large field of view, is in an excellent position to follow up on these interesting studies.