• Title/Summary/Keyword: Black Hole

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A Study of Kinetic Effect on Relativistic Shock using 3D PIC simulation

  • Choi, Eun-Jin;Min, Kyoung-Wook;Choi, Cheong-Rim;Nishikawa, Ken-Ichi
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.1
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    • pp.67.1-67.1
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    • 2012
  • Shocks are evolved when the relativistic jets in active galactic nuclei (AGNs), black hole binaries, supernova remnants (SNR) and gamma-ray bursts (GRBs) interact with the surrounding medium. The high energy particles are believed to be accelerated by the diffusive shock acceleration and the strong magnetic field is generated by Weibel instability in the shock. When ultrarelativistic electrons with strong magnetic field cool by the synchrotron emission, the radiation is observed in gamma-ray burst and the near-equipartitioned magnetic field in the external shock delays the afterglow emission. In this paper, we performed the 3D particle-in-cell (PIC) simulations to understand the characteristics of these relativistic shock and particle acceleration. Forward and reverse shocks are shaped while the unmagnetized injecting jet interacts with the unmagnetized ambient medium. Both upstream and downstream become thermalized and the particle accelerations are shown in each transition region of the shock structures.

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A Study on Gas-Assisted Plastic Injection Mould of Flat TV Front Cover (Flat TV Front Cover의 Gas 사출 금형에 대한 연구)

  • 문영대
    • Transactions of Materials Processing
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    • v.12 no.8
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    • pp.738-743
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    • 2003
  • The major problems of a plastic injection mould can be devided into two kinds, one is in mould another in injected parts. Most of defects of the former comes from mould design, such as, structure and working. The latter are weld line, warpage, sink mark, burning, flow mark, scratching, shading, black hole and so on. Most of problems in injection molding are difficult to find the reason because of complexity. The purpose of this paper is to improve the quality of plastic injection mould and parts with inquiring the counter plan and analizing troubles of the part of Flat TV Front Cover by flow control method and gas-assisted injection moulding. For minimizing defects of the injection moulded parts, computer aided simulation method for injection mould filling was used. Based on these numerical results, the guidelines of mould design and injection processing condition were established. As a result, the improvement of quality, such as minimizing surface defects of injection moulding parts and troubles in mould was achieved.

AKARI Spectroscopic Study of the Rest-frame Optical Spectra of Quasars at 3 < z < 5

  • Jun, Hyun-Sung;Im, Myung-Shin;Lee, Hyung-Mok;QSONG team, QSONG team
    • The Bulletin of The Korean Astronomical Society
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    • v.35 no.1
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    • pp.78.1-78.1
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    • 2010
  • We present the initial results of rest-frame optical spectroscopy of quasars at 3 < z < 5 from the AKARI space telescope mission program QSONG (Quasar Spectroscopic Observation with NIR Grism). QSONG is an AKARI phase-3 mission program which utilizes the unique capability of spectroscopy at 2.5-5 microns, and is adequate for detecting redshifted Balmer lines. We focus on how to overcome the noise induced from instrumental degradation, and report our measurements of supermassive black hole (SMBH) masses with well calibrated optical mass estimators.

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Observing the central engine of GRB170817A

  • van Putten, Maurice H.P.M.
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.1
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    • pp.39.2-39.2
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    • 2018
  • GW170817/GRB170817A establishes a double neutron star merger as the progenitor of a short gamma-ray burst, starting 1.7 s post-coalescence. GRB170817A represents prompt or continuous emission from a newly formed hyper-massive neutron star or black hole. We report on a deep search for broadband extended gravitational-wave emission in spectrograms up to 700 Hz of LIGO O2 data covering this event produced by butterfly filtering comprising a bank of templates of 0.5 s. A detailed discussion is given of signal-to-noise ratios in image analysis of spectrograms and confidence levels of candidate features. This new pipeline is realized by heterogeneous computing with modern graphics processor units (GPUs). (Based on van Putten, M.H.PM., 2017, PTEP, 093F01.)

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Ionized gas outflows in z~2 WISE-selected Hot Dust Obscured Galaxies

  • Jun, Hyunsung
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.1
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    • pp.37.2-37.2
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    • 2018
  • The Wide-field Infrared Survey Explorer (WISE) mission has been efficient in selecting Active Galactic Nuclei (AGN) with high luminosities and large obscuration. According to the merger driven AGN powering scenarios, luminous and obscured AGN are in a stage where they go through feeding of gas accretion into the central black hole, and feedback to the host galaxy through outflows. We report the rest-frame UV-optical spectra of 11 Hot Dust Obscured Galaxies (Hot DOGs) at z~2, WISE color-selected to be extremely reddened AGN. A fraction of the targets show blueshifted and broadened [OIII] profiles indicative of ionized gas outflows. We present the occurrence and strength of the outflows, and discuss what impact these AGN activity could give on their hosts.

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Radial distribution of blue straggler stars in Magellanic Cloud clusters

  • Hong, Jongsuk
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.1
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    • pp.46.2-46.2
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    • 2018
  • Using the high-resolution observational data obtained by the Hubble Space Telescope, we found that there is the diversity of the radial trends of blue straggler stars (BSSs) in young massive clusters (YMCs) in the Large Magellanic Cloud unlike BSSs in old globular clusters usually showing the segregated radial distributions. To understand the dynamical processes that lead to the none-segregated or even inversely-segregated radial distribution of BSSs, we performed direct N-body simulations for YMCs. Our numerical simulations show that the presence of black hole subsystems inside the cluster centre can significantly affect the dynamical evolution of BSSs and eventually lead to none- or inversely-segregated radial distribution of BSSs.

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Study on Shape Optimization Using Finite Elements Addition and Removal (요소가감법을 이용한 형상최적설계에 관한 연구)

  • Kim, Young-Jin;Lim, Kyeong-Ho
    • Proceedings of the KSME Conference
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    • 2000.11a
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    • pp.486-491
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    • 2000
  • In this study, finite elements addition and removal method by stress range is applied to optimize shapes in structures, without using classical and numerical optimization methods and search methods. The program based on this algorithm is developed and compared to theoritial results with considerable accuracy. Classical methods need mesh generation for finite element analysis for every iteration, the developed method needs updated mesh data such as coordinates of nodes, elements connectivity, and loads on nodes. And other tools of finite element analysis can be in use as a black box to interface with this program.

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Radiation Hydrodynamics of 2-D Accretion Disks

  • OKUDA TORU
    • Journal of The Korean Astronomical Society
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    • v.34 no.4
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    • pp.251-254
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    • 2001
  • To examine the structure and dynamics of thick accretion disks, we use a two-dimensional viscous hydrodynamic code coupled with radiation transport. The $\alpha$-model and the full viscous stress-tensor description for the kinematic viscosity are used. The radiation transport is treated in the gray, flux-limited diffusion approximation. The finite difference methods used are based on an explicit-implicit method. We apply the numerical code to the Super-Eddington black-hole model for SS 433.@The result for a very small viscosity parameter a reproduces well the characteristic features of SS 433, such as the relativistic jets with $\~$0.26c, the small collimation degree of the jets, the mass-outflow rate of ${\ge}5{\times}10^{-7}M{\bigodot}yr^{-1}$, and the formation of the X-ray iron emission lines.

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Host Galaxies of Nearby Type I AGNs

  • Kim, Min-Jin;Ho, Luis;Peng, Chien;Barth, Aaron;Im, Myung-Shin
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.68.2-68.2
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    • 2011
  • We present the detailed image decomposition of Hubble Space Telescope archival images for 235 nearby (z < 0.35) unobscured type 1 AGNs. It allows us to perform robust measurements of host galaxy properties and AGN luminosity contribution. We examine how the host properties correlate with AGN properties. Broad line type 1 and radio-loud AGNs are hosted preferentially by early type galaxies. Narrow line type 1 AGNs show a low fraction of tidal interaction, that might suggest the secular evolution may play an important role for triggering AGN activity, while the fraction of merging hosts is rather higher in luminous AGNs. We compare the nucleus luminosity and bulge luminosity and find that either our sample might have a smaller zero point in the M(BH)-L(bulge) relation (i.e. less massive black hole at a given bulge luminosity) relation compared to the normal galaxies or Eddington ratio of our sample could be systematically overestimated.

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A NEW CLASS OF NEUTRON STAR BINARIES AND ITS IMPLICATIONS

  • LEE, CHANG-HWAN
    • Publications of The Korean Astronomical Society
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    • v.30 no.2
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    • pp.573-576
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    • 2015
  • Recent discovery of $2M_{\odot}$ neutron stars in white dwarf-neutron star binaries, PSR J1614-2230 and PSR J0348+0432, has given strong constraints on the maximum mass of neutron stars. On the other hand, all well-measured neutron star masses in double neutron star binaries are still less than $1.5M_{\odot}$. These observations suggest that the neutron star masses in binaries may depend on the evolution process of neutron star binaries. In addition, recent works on LMXB (low-mass X-ray binaries) provides us the possibility of estimating the masses and radii of accreting neutron stars in LMXBs. In this talk, we discuss the implications of recent neutron star observations to the neutron star equation of states and the related astrophysical problems. For the evolution of neutron star binaries, we also discuss the possibilities of super-Eddington accretion onto the primary neutron stars.