온도를 낮추고자 하는 이유는 여러 가지가 있다. 미생물의 번식을 막기 위해서, 음식의 장기 보존을 위해서, 식품 가공을 위해서, 식물의 생장을 억제하기 위해서, 부피를 줄여서 보관하는 공간을 절약하기 위해서, 뻘과 같은 질척한 토질에서 굴착을 위한 토목공사를 용이하게 하기 위하여, 피부의 탄성을 좋게 하기 위하여, 물질의 강도를 높이기 위하여, 물질의 전기저항을 줄이기 위하여, 온도를 낮춤으로 나타나는 상변이, 양자현상 현상들을 보기 위하여, 전자기기 등의 잡음을 줄이기 위하여, 물질의 미세 진동을 줄이기 위하여 등등... 이러한 저온을 얻기 위한 기본적 방법은 열전달을 억제하기 위한 대류, 전도, 복사와 같은 기본 조건들을 제어함으로 얻어질 수 있다. 여기에는 물질의 열적 성질에 대한 지식과 온도를 낮춤으로 일어나는 물질의 수축, 그리고 구조적 변형 등 온도변화에 따른 제반 상태에 대한 이해가 필요하다. 국내에서는 초전도 기술의 발전과 응용에 의해 극저온 기술의 발전이 크게 진전하였다. 2000 년대에 들어서면서 대형 초전도자석이 핵심장비인 KSTAR 와 같은 대형 구조물의 극저온 냉각, MRI, 가속기용 초전도 자석 냉각, 고온초전도 선재를 이용한 전력 송전용 케이블의 냉각 등의 개발을 들 수 있으며, 이외에도 반도체 라인에서의 clean vacuum 을 위한 냉각기술, 식품가공 등을 위한 냉동기술,  LNG 의 대량 수송을 위한 액화기술 등을 들 수 있다. 중력파 탐사 등 미세한 신호를 검출하기 위한 실험에서는 검출기 자체의 검출한계를 높이기 위한 노력과 더불어 검출기 및 실험장치에서의 잡음 감소와 검출 한도를 높이기 위하여, 초기에 상온에서의 검출 한계를 극복하기 위해 저온으로 냉각하기 시작하였으며, 극한적으로 양자잡음을 줄이기 위해 ~mK 영역에까지 도달하고자 노력하고 있다. 이와 관련한 냉각기술에 대하여 논의하고자 한다.

I will discuss the central dark matter distribution of dwarf galaxies in the local Universe within 10 Mpc derived using their resolved kinematics from Very Large Array (VLA) HI galaxy surveys in tandem with Spitzer 3.6 micron and optical observations. The degree of the central dark matter concentration of the galaxies quantified by measuring their inner density slopes indicates a mass distribution with a sizeable constant density-core towards the centres of the galaxies. This is in contrast to classical dark-matter-only cosmological simulations where cusp-like dark matter distribution is predicted in the halos. Instead, our results are more in line with shallower slopes found in Lambda CDM simulations of dwarf galaxies in which the effect of baryonic feedback processes is included. I will the talk with the discussion of science cases that I plan to carry out at KASI in order to timely prepare for the upcoming SKA era as well as best exploit the observing facilities currently accessible at KASI.

 Very rapid (100) variability at >1e40 erg/s is nearly unprecedented in our Universe. We have recently discovered a new class of X-ray point sources showing such variability in two nearby galaxies while analyzing archival Chandra and XMM-Newton data. One source is located within a suspected globular cluster of the host galaxy and flared one time, while the other source is located in either a globular cluster of the host galaxy or the core of a stripped dwarf companion galaxy that flared on five occasions over a seven year time span. When not flaring, the sources appear as normal accreting neutron star or black hole X-ray binaries, indicating that the flare event does not significantly disrupt the system. We speculate on the nature of these explosive, yet non-destructive objects.

I shall introduce three new techniques of magnetic field tracing. The first two use Doppler-shifted emission lines and employs the gradients of velocity in order to trace magnetic fields in the diffuse interstellar media as well as to trace regions of star formation associated with the gravitational collapse. The differences between these techniques is that they use different observationally available measures, i.e. the first one uses the velocity centroids and the other uses velocity channel maps. I shall provide the theoretical justification of the use of these measures, its numerical testing as well as the comparison of the directions obtained with the velocity centroid gradients using GALFA HI data and those of magnetic field as traced by Planck as well as 13CO data and far infrared polarimetry. I shall also discuss the third technique which employs the synchrotron intensity gradients that also trace magnetic field and, unlike synchrotron polarization, are insensitive to Faraday rotation. I shall also show its correspondence with the magnetic field tracing by Planck and discuss the synergy of using this technique with synchrotron polarization studies. I shall discuss the big promise of the new techniques both for the star formation and CMB foreground studies. 

Detection of gravitational waves (GWs) from binary black holes (BHs) by Advanced LIGO has opened a new window of astronomical observation. Many conceivable sources such as intermediate-mass BH binaries and white dwarf binaries, as well as stellar-mass BH inspiral, would emit GWs below 10 Hz. It is highly desirable to open a new window in the infrasound frequency band below 10 Hz. A low-frequency tensor detector could be constructed by combining six magnetically levitated superconducting test masses. Seismic noise and Newtonian gravity noise are serious obstacles in constructing terrestrial GW detectors at low frequencies. A tensor detector can reject the near-field Newtonian gravity noise more efficiently. Such a detector is equally sensitive to GWs coming from anywhere in the sky, and is capable of resolving the source direction and wave polarization. I will present a design concept of a new low-frequency detector, named SOGRO, which could reach a strain sensitivity of 10-19-10-21 Hz-1/2 at 0.1-10 Hz. I will discuss ways to mitigate the seismic and Newtonian noise, as well as foreseeable technical challenges and limitations in developing such a detector.

Galaxy evolution is the grandest of all environmental sciences. Just how a galaxy forms and evolves in a given environment is one of the most pressing unanswered questions in astrophysics. This talk will describe plans to address this question through the construction of a new and unrivalled multi-object integral field unit (IFU) spectrograph for the 3.9m Anglo-Australian Telescope (AAT) called HECTOR. This instrument will make it possible to obtain IFU spectros of unprecedented quality for many tens of thousands of galaxies, that will make it possible to fully understand the physical basis for the diversity of galaxy properties. This will build on the heritage of the very successful but much smaller SAMI survey of ~3,000 galaxies currently being conducted on the AAT. As well as describe the science drivers and hence design requirements for HECTOR, I will also discuss the opportunity for Korea to partner with Australia in the construction of HECTOR and the realisation of its science, something the Australian astronomy community would warmly welcome. 

It is widely believed that magnetic fields play a crucial role for the dynamics of molecular clouds and for the star formation processes. One of the most informative techniques of studying magnetic fields in molecular clouds and protostellar disks is based  on the use of polarized emission arising from magnetically aligned dust. In this talk, I will talk about the Chandrasekhar-Fermi (CF) method, which is a simple and powerful technique to measure magnetic field strength from FIR/sub-mm polarization observations. I will demonstrate that the conventional CF method tends to overestimate the strength of the magnetic field and describe how to correct the tendency. When time permits, I’ll briefly talk about polarized emission from T Tauri disks.

Interstellar nanoparticles, including polycyclic aromatic hydrocarbons (PAHs), are believed to play an important role in modern astrophysics. Mid-infrared emission from PAHs is widely used as a tracer of star formation activity. PAHs is also thought to be a leading carrier behind the long-standing mystery of Diffuse Interstellar Bands (DIBs).  In this talk, I will discuss new insights into the crucial importance of interstellar nanoparticles. I will start with a review on anomalous microwave emission (AME) by rapidly spinning nanoparticles, which is a critical challenge for early universe study via cosmic microwave background (CMB) radiation. Then, I will present a new way to tracing magnetic fields via polarized mid-IR emission from PAHs. Finally, I will discuss future perspectives to study interstellar nanoparticles through multiwavelength observations with Square Kilometer Array and ALMA Band 1.

The substorm is a dissipation process of the energy stored in the magnetotail, causing active auroras in the nightside polar regions. What processes in the magnetotail trigger the substorm is a major issue in magnetospheric research and has been extensively debated for decades. To understand the substorm triggering mechanism, I statistically studied substorm-associated evolution of the near-Earth magnetotail, using more than ten years of plasma, and magnetic and electric field data mainly from the Geotail spacecraft. I also analyzed data from the recent five THEMIS spacecraft. My results revealed the overall morphological picture of substorm-associated magnetotail evolution as well as energy release and transport and clarified that magnetic reconnection in the near-Earth magnetotail plays an essential role in substorm triggering.

While morphology has been the dominant property to describe and classify galaxies, spin is emerging newly as an alternative and perhaps more fundamental property of a galaxy. Integral field unit spectros revealed that the majority of elliptical galaxies do have a substantial rotational component unlike previous understanding. I present a new result from cosmological-volume hydrodynamic simulations and discuss the origin of spin of galaxies.

The Hyper-Kamiokande (Hyper-K) is a next generation experiment based in Japan succeeding the Super-Kamiokande (Super-K) experiment which achieved the 2015 Nobel prize.  It will consists of two identical 260 kton water Cherenkov detectors, 20 times bigger than Super-K,  to cover particle physics to astronomy.  The main goals are to solve important problems remaining in neutrino physics using J-PARC neutrino beam, and to detect Super Nova burst/relic neutrinos as well as to search for proton decay and dark matter. Hyper-K is indeed a multi-purpose experiment and telescope from precise measurements to new discoveries.  If one of the detectors is located in Korea instead of the two in Japan, then the physics sensitivities will improve. World-class discoveries are expected and Korea will play a critical role by co-leading the experiment.  There are several good candidate sites in Korea to host a Hyper-K detector thanks to higher mountains to reduce spallation background and better quality of rocks to excavate than Japan.  In this talk I will focus on the Hyper-K as a neutrino telescope which will run for 30 years or more. p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; -webkit-text-stroke: #000000} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; -webkit-text-stroke: #000000; min-height: 14.0px} span.s1 {font-kerning: none}

Initially stimulated by the predictions of high resolution LCDM simulations (e.g. Millennium and Aquarius) and then dramatically advanced by scrutinizing large digital imaging data sets such as SDSS, Pan-STARRS, and  the Dark Energy Survey, our picture of the Milky Way and its satellite population has dramatically changed in the past decade. After an overview of our historical understanding of the Milky Way and its dwarf galaxies  I will reflect over the tremendous progress in the emerging field of ultra-faint stellar systems, present the most fascinating results we were able to obtain and discuss the new mysteries waiting for us to be solved in future research. This colloquium is partly supported by the BK21 Plus of Chungnam National University.

2016년 12월 31일 기준으로 인터스텔라의 누적 관객수는 10,304,503명으로 천만 관객 이상 영화로는 역대 15위입니다. 인터스텔라 흥행의 성공 요인은 천체물리학이나 양자역학 등 방대한 과학 주제들을 3시간에 걸쳐 뛰어난 visual effect로 보여 주었다는 것입니다. 영화 인터스텔라의 제작에서 킵손 박사와 영국의 Double Negative라는 시각효과 회사가 협업을 한 것처럼, 국내의 척박한 과학 콘텐츠 현실에서도 어려운 천체물리학을 computer graphics를 이용한 표현을 통해서, 대중에게 소개하는데 새로운 기회를 마련할 수 있을 것으로 예상해 봅니다. 웜홀, 중력렌즈, 빅뱅 등 이해하기 힘든 천체물리학의 주제들을 시각적으로 표현하는 것은 그 자체로도 의미가 있고, 이러한 노력은 학문의 분야에만 제한되지 않고 학계가 대중에게 천체물리학을 소개하는 과정에서 관심을 두어야 하는 부분입니다. 이번 강연에서는 천체물리학을 전공한 연구자가 Double Negative와 협업으로 성공적인 과학 콘테츠를 제작할 수 있었던 것처럼, LG엔시스가 virtual reality 천문우주 과학 콘테츠 제작에 대해서 가지고 있는 계획 등을 소개하도록 하겠습니다. LG엔시스에서는 가상현실 몰입감을 극대화 하고 대중화를 위한 방안으로 4D 모션체어 기반 HMD(Head-Mounted Display), 반구형 돔(Dome)을 제안하고 있습니다. 4D 모션체어 기반 HMD, 반구형 돔이 어떻게 천문우주 과학 콘텐츠 확산하는데 대안이 될 수 있는지 알아보도록 하겠습니다.

In 2016, LIGO group announced the detections of gravitational waves (GWs).  This was not only the first observation of gravitational wave, but also the first direct evidences of black hole (BH), and BH binaries. We plan to apply GW observations to specify the formation model of a super-massive BH (SMBH). First, we explain the expected observational profiles of gravitational wave at ground-based detectors, such as KAGRA or advanced LIGO/VIRGO. We then explain our dynamical formation model of a SMBH and its plausibilities. We, then, estimate the number density of galaxies from halo formation model, and  estimate the number of BH mergers from giant molecular cloud model together with hierarchical growth of merged cores. Taking account the detector's sensitivities, we finally discuss event rates of GWs based on our scenario. Our conclusion is that the statistics of the signals will tell us both a galaxy distribution and a formation model of SMBHs. Especially, if we detect a BH with more than 100 M_solar in future gravitational wave observations, our model naturally explains its source.

Whether supernovae (SNe) are a significant source of dust has been a long-standing debate. I will review  infrared observations of the young supernova remnants (YSNRs) -- Cas A, SNR 1E102.2-7219 (E0102), N132D, and the Crab Nebula using Spitzer and Herschel data. These SNRs reveal evidence of dust formation and presence of cold dust, and show that SNe are important sites of dust formation and produce dust on short time-scales. I will present detection of cold dust from another Crab-like SNR, G54.1+0.3, using Spitzer and Herschel data, and a revisit of the dust mass in Cas A with the first spatially resolved analysis of Cas A based on Spitzer and Herschel infrared and submillimetre data. I will discuss  dust features and composition, total dust masses, and a significance of supernovae dust in the early Universe and galaxies. I will also present the introduction of the  LSST project, the LSST observing strategy and its optimization for SN cosmology and SN science, and ideas of the LSST follow-up optical/infrared spectros.

As ALMA is in full operational mode, the SMA continues to be a most valuable asset in submillimeter wavelength astronomy. In particular, for wide-field imaging, for polarization studies, and for large spectral scans, the SMA is competitive especially for the northern skies. Starting in 2017, the ASIAA invites all astronomers in the East Asian regions to join in the access to the SMA as part of an initiative within the East Asian Observatory. In this talk, we will show current capabilities and future plans for improvement in sensitivity.

기초과학 연구가 대형 연구 장비에서 생산되는 대용량 데이터를 처리하여 자연현상을 기술하는 데이터기반 연구로 패러다임이 변화하고 있다. 데이터기반 연구가 부상함에 따라 개방성이 중요해 지고 있으며 최근 OECD는 Open Data, Open Access, Open Collaboration을 통해 Open Science로 그 가치를 실현하고자 과학정책에 반영하는 활동을 하고 있다. 글로벌 대용량 실험데이터 허브센터(GSDC)는 국가 유일의 기초과학분야 데이터집약형 데이터 센터이며 CERN의 최상위 데이터센터인 WLCG Tier-1의 기능을 수행해오고 있다. 다양한 기초과학분야 지원을 강화하고 통합데이터센터로의 역할을 확대해 나가고 있는 중이다. 본 콜로퀴움에서는 GSDC에 대한 소개를 중심으로 오픈사이언스 시대의 한국의 데이터센터의 역할에 대해 소개 하고 천문연구자와 협력모델에 대해 의견을 수렴하여 GSDC 발전방향에 반영 하고자 한다

The geodetic VLBI technique is capable of measuring the Sun's gravity light deflection from distant radio sources around the whole sky. This light deflection is equivalent to the conventional gravitational delay used for reduction of geodetic VLBI data. Numerous tests based on a global set of VLBI data have shown that the parameter gamma of the post-Newtonian (PPN) approximation is equal to unity with precision of about 0.02 percent. However, the estimated accuracy is mostly dominated by the limited number observations near the Sun. I have processed 56 geodetic VLBI sessions between 1993 and 2005 when a reference radio source was observed within 5 degrees from the Sun (1662 single group delays in total) using different analysis strategies. The parameter gamma is still found to be close to unity with precision of 0.06 per cent, whereas subsets of VLBI data measured at short and long baselines produce some statistical inconsistency. In particular, at a shorter range of baseline length, the formal error is better (0.04 per cent) in spite of a less number of observations. This effect depending on baseline length may highlight some deficiency of the conventional VLBI group delay model, rather than a problem of the theory. Nonetheless, more observations near the Sun are important to improve the formal error of the PPN parameter gamma.

Stars are born with protostellar discs that during the initial stages of their formation are relatively massive, asymmetric and they are being fed with material infalling from their parent clouds. Recent ALMA observations of discs around young stars revealed the presence of gaps and spiral arms indicative of planet formation. These observations raise the exciting possibility that planets may form much faster than it has been previously thought. Therefore, their formation may be sensitive to the early properties of discs while they are still forming in collapsing molecular clouds. I will present radiative hydrodynamic simulations of self-gravitating discs forming in collapsing clouds and discuss their observational signatures. I will also discuss how giant planets that form in early phase discs evolve. Can such planets avoid fast inward migration and fast mass growth to survive until after the disc has dispersed?

영화 로 유명한 위대한 상대론적 천체물리학자 Kip Thorne의  업적을 중심으로 black hole electrodynamics의 역사와 토픽에 대하여 알아보기로 한다. 가능한 한 수식 없이 주로 그림들을 이용하여 전공자가 아니어도 들을 수 있게 눈높이를 낮춰 설명할 계획이다.

Future cosmic surveys of large scale structure and the cosmic microwave background radiation will attempt to answer questions of fundamental physics: What is the nature of dark energy? Is cosmic gravity completely described by general relativity? Can we probe the inflationary epoch through primordial gravitational waves? What are the masses and hierarchy of neutrinos and are there additional relativistic degrees of freedom? We need to develop the theoretical, computational, and technological frameworks to address the questions. I also describe the Cosmic Visions process in the US, for what might come beyond the DESI-Euclid-LSST-WFIRST era for dark energy and the CMB.

In this talk, I will introduce our new simulation suites called TIGRESS, "Three-phase ISM in Galaxies Resolving Evolution with Star formation and Supernova feedback." TIGRESS models a realistic turbulent, magnetized, multiphase ISM in galactic disks with self-consistent treatment for star formation and supernova feedback. I will discuss star formation rates and ISM properties regulated by star formation feedback and the properties of the multiphase outflows driven by SNe. I will also discuss future applications and extensions of TIGRESS.

Evolved stars in the Asymptotic Giant Branch (AGB, a crucial phase in the late evolution of most stars, including solar-type stars) present copious mass-loss processes, which finally lead to the ejection of most of the stellar mass and drive the end of that phase and the formation of planetary nebulae around white dwarf stars. During the AGB phase, the ejection is significantly isotropic, leading to wide spherical shells that are radially expanding with moderate velocities. The crucial regions to study these phenomena are the very inner circumstellar layers, where the mass loss process is actually taking place. These regions can be observed with very high resolution, better than one milliarcsecond, thanks to VLBI observations of maser lines. I will review recent studies in this field of our group, stressing the interest of simultaneous observations of different lines and of high accuracy astrometry. We have recently found a surprising very fast variability in some objects, future VLBI studies of this phenomenon will be discussed.

We have long assumed that stars form by gravitational collapse but hard evidence of infalling motions has been elusive. The Bok Globule, B335, has been the test bed for studies of simple isolated star formation. Our ALMA Cycle 1 observations of this source have revealed definitive kinematic evidence for infall in the form of redshifted absorption against the continuum source. Approximately spherical infall appears to extend inward to about 16 AU. Further studies of this and other sources will allow us to study the velocity fields of infalling matter and the transition to a rotationally supported disk, possibly through the formation of a magnetically supported pseudo-disk.

Accretion is the best model to explain the high luminosity, spectra and timing properties of AGNs and microquasars. Accretion is supposed to be the prime reason also for the ejection of jets associated with these objects. We review the phenomenology of these objects based on observations, and discuss the likely scenario to explain these phenomena. We also discuss the limitations of our understanding about these objects.

In the last two decades, the asteroid research has been significantly influenced by theoretical results obtained in the field of applied mathematics. The first step was the so called "lightcurve inversion", which is an inversion method that reconstructs a shape of an asteroid from its disk-integrated photometry. With this method, almost one thousand asteroid models have been derived so far. Its potential is much larger - it will enable us to reconstruct shapes and spin states of a significant fraction of the whole asteroid population. Together with photometry, other disk-resolved (low-resolution images, silhouettes from occultations,...) or disk-integrated data (thermal infrared flux, for example) can be analyzed and detailed models can be derived by so called "multi-modal data inversion". In this talk, I will (i) review lightcurve inversion method, (ii) highlight the main achievements accomplished in the asteroid research with lightcurve inversion, (iii) describe the role of disk-resolved data, and (iv) mention the plans and prospects for the future, in particular the cooperation within the KMTNet and LSST projects.

The acceleration of the expansion of the Universe, driven by the mysterious Dark Energy, indicates that our theory of gravity may need revision. While Einstein’s theory passes precision tests on Solar System scales, it seems to break down or require some extra component on the very largest scales. It is possible to test gravity in the Universe in the same manner as on Earth and in the Solar System, by watching test particles (galaxies, and photons) fall towards more massive objects. The theory of structure formation describes how tiny perturbations in the density of matter grow under gravitational collapse to form the structures that we see today. In this talk I will introduce the  2-degree Field Lensing Survey (2dFLenS) is a large area spectroscopic galaxy survey, describe how measurements made using the survey can be used to test gravity, and report on some tentative initial results.

The Atacama Large Millimeter/submillimeter Array (ALMA) is an aperture synthesis interferometer that currently operates from wavelengths of 3 mm to 350 microns with up to sixty-six (66) array elements, fifty-four (54) of 12-m diameter and twelve (12) of 7-m diameter. The array is located at the ALMA Array Operations Site (AOS) on the Chajnator plateau (at an altitude of about 5000 meters) in the Atacama desert in northern Chile. While the antennas and most of the hardware for the receivers are on site, array capabilities are still expanding and the observatory is ramping up towards full operations. Early science observations have been ongoing since October 2011 and today ALMA is in its fourth Cycle of Early Science observations. Many exciting, fundamental results have already been obtained from the solar system to the early universe. I will review the current status of the project, the array performance and efficiency, recent testing results, on-going development projects as well as sketching future developments that will enable ALMA to extend the frontiers of science even further. In short, I will present ALMA: Past, Present and Future.

The origin and evolution of the circumstellar disk around protostars informs the origin and evolution of planets. Only recently, have we even detected the youngest circumstellar disks, but their frequency and typical properties (i.e. mass and size) are still not known. With our new high-resolution millimeter surveys of protostars, we now have about 20 young disks with radii > 15 AU. However, these only represent less than ¼ of the population in our surveys. One possible explanation for small disks (< 15AU) in the youngest sources is magnetic braking of material at the earliest stages. In this talk, I explore the early evolution of the disk, implications for dust growth, and discuss future surveys.

Star formation covers a huge size scale. From the large giant molecular cloud complex of several tens of parsecs to the protostars at the order of solar radius, it is about 9 orders of magnitude in spatial scale. In between, we observe long filamentary dark clouds, large molecular cloud clumps, dense cloud cores that house the formation of protostars, and protostellar accretion disks. Multiply coupled highly non?linear physics are involved in the star formation process, including magnetic field, supersonic turbulence, gravity, radiation and protostellar outflow feedback. Numerical simulation has become a powerful tool to understand and connect these observational snapshots of the entire star formation process. Still, it is a challenge to simulate the entire process in a single simulation. To achieve such a long?term challenge, we need efficient adaptive codes, such as adaptive mesh refinement (AMR) code, that can manage memory usage efficiently and are highly scalable on large?scale high performance supercomputers. In this talk, I present my latest cluster formation simulation results, using our radiative?magnetohydrodynamics AMR code "ORION2", to understand (1) the intertwined filamentary structure of dark clouds, (2) the magnetic properties of the dense cloud clumps, and (3) the protostellar cluster formation in a highly supersonic turbulence region of about 4.6 parsecs in size with the highest resolution of 28 astronomical units. The simulation results match well with latest observations and provide important insight into the process of star formation at different size scales that cannot be easily obtained from observations.