• 천문학회보
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• 제39권1호
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• pp.79.1-79.1
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• 2014

GRBs are the most energetic and very frequent electromagnetic events among known astronomical phenomena in the universe. The progenitor of GRBs is believed as one of most promising sources of gravitational waves. Thus, detection of gravitational wave signals associated with GRBs will be a fascinating issue. In this presentation, we describe how we search gravitational waves related to GRBs by using LIGO and Virgo data.

• 문화기술의 융합
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• 제5권1호
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• pp.385-388
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• 2019

5 차원 정적 다양체에 내재된 구형 대칭적인 시공간을 고려하여, 변형된 중력 이론의 하나인 DGP (Dvali, Gabadadze, and Porrati) 모형의 원거리 근사에서 측지선 방정식을 연구 하였다. 널(null) 측지선 방정식을 분석하여, 4차원 시공간에서 입자들의 유효 질량과 전달 속력을 구했다. 아인슈타인 일반상대론적 중력 이론을 규명하게 되는 중요한 업적 중에 하나인, 최근에 관측된 중력파 발견의 결과들과 측지선을 따르는 입자들의 관계성을 논의하였다. 4차원 시공간에서 전파되는 전자기파의 전달과 비교 검토 하였다.

• 천문학논총
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• 제26권2호
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• pp.71-87
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• 2011

Gravitational waves are predicted by the Einstein's theory of General Relativity. The direct detection of gravitational waves is one of the most challenging tasks in modern science and engineering due to the 'weak' nature of gravity. Recent development of the laser interferometer technology, however, makes it possible to build a detector on Earth that is sensitive up to 100-1000 Mpc for strong sources. It implies an expected detection rate of neutron star mergers, which are one of the most important targets for ground-based detectors, ranges between a few to a few hundred per year. Therefore, we expect that the gravitational-wave observation will be routine within several years. Strongest gravitational-wave sources include tight binaries composed of compact objects, supernova explosions, gamma-ray bursts, mergers of supermassive black holes, etc. Together with the electromagnetic waves, the gravitational wave observation will allow us to explore the most exotic nature of astrophysical objects as well as the very early evolution of the universe. This review provides a comprehensive overview of the theory of gravitational waves, principles of detections, gravitational-wave detectors, astrophysical sources of gravitational waves, and future prospects.

• 천문학회보
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• 제36권1호
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• pp.70.1-70.1
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• 2011

During the summer of 2010, the first low-latency search for gravitational waves from compact binary coalescences was performed using the LIGO and Virgo instruments. The aim was to provide triggers for follow-up by electromagnetic telescopes. In this presentation we will describe the low-latency pipeline used to produce these triggers, including the time-delay-based procedure used to localize them on the sky.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1197-1210
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• 2018

Since the first detection of gravitational-wave (GW), GW150914, September 14th 2015, the multi-messenger astronomy added a new way of observing the Universe together with electromagnetic (EM) waves and neutrinos. After two years, GW together with its EM counterpart from binary neutron stars, GW170817 and GRB170817A, has been observed. The detection of GWs opened a new window of astronomy/astrophysics and will be an important messenger to understand the Universe. In this article, we briefly review the gravitational-wave and the astrophysical sources and introduce the basic principle of the laser interferometer as a gravitational-wave detector and its noise sources to understand how the gravitational-waves are detected in the laser interferometer. Finally, we summarize the search algorithms currently used in the gravitational-wave observatories and the detector characterization algorithms used to suppress noises and to monitor data quality in order to improve the reach of the astrophysical searches.

• 천문학회보
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• 제41권1호
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• pp.31.3-31.3
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• 2016

Exploring a universe with gravitational waves (GWs) was only theoretical expectation for long time. In September 2015, the Laser Interferometer GW Observatory (LIGO) first detected GWs emitted from the collision of two stellar-mass black holes in cosmological distance (1.3 billion light years) on Earth. This confirms the existence of black-hole binary mergers, and further, opens a new field of GW astronomy. We begin our discussion with a list of important GW sources that can be detectable on Earth by large-scale laser interferometers such as LIGO. Focusing on compact objects such as neutron stars and black holes, we then discuss possible research in the context of GW astronomy. By coordinating with existing observatories, searching for electromagnetic waves or particles from astronomical objects, around the world, multi-messenger astronomy for the universe's most cataclysmic phenomena (e.g. gamma-ray bursts) will be available in the near future.

• 천문학회보
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• 제39권1호
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• pp.78.1-78.1
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• 2014

Pulsar binaries in tight orbits are considered to emit strong gravitational waves (GWs) during the last stage of their coalescences. They form a subset of compact binary mergers, which consists of white dwarfs (WDs), neutron stars (NSs), or black holes (BHs). One of the most famous example of 'merging' pulsar binaries is the Hulse-Taylor pulsar (PSR B1913+16) discovered in 1974 by Russell Hulse and Joseph Taylor. About ten NS-NS and several tens of NS-WD binaries are known in our Galaxy. Merging binaries are rare and only a few NS-NS and NS-WD have been discovered to date. A pulsar with a black hole companion is also theoretically expected, but there is yet no detection. Within several years, direct detections of GWs from compact binary mergers will be made by laser interferometers. This will pave a way to study physics of compact binaries that cannot be reached by electromagnetic waves (EM). Pulsar binaries are of particular interest as we can use both EM and GW to probe these systems. In this talk, we present a brief overview on the Galactic pulsar populations and discuss their implications for GW detection.

• 천문학회지
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• 제51권5호
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• pp.165-170
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• 2018

The Galactic Center is one of the most dense stellar environments in the Galaxy and is considered to be a plausible place to harbor many neutron stars. In this brief review, we summarize observational efforts in search of neutron stars within a few degrees about the Galactic Center. Up to 10% of Galactic neutron stars may reside in this central region and it is possible that more than a thousand neutron stars are located within only ~ 2500 (${\leq}1pc$) about the Galactic Center. Based on observations, we discuss prospects of detecting neutron stars in the Galactic Center via gravitational waves as well as electromagnetic waves.

• 천문학회보
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• 제43권1호
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• pp.55.2-55.2
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• 2018

Neutron stars (NS) are rapidly spinning compact objects. Their rotation energy is released by particles, electromagnetic waves, and even gravitational waves. The source of the energy is of course the rotation, so by studying the rotational properties of neutron stars, we can gain some insights into matter under extreme conditions. In particular, it is known that the braking index n is sensitive to the moment of inertia and/or NS winds. The neutron star PSR B0540-69 exhibits interesting timing behavior; previous measurements of the braking index for this pulsar may suggest a change in time. In order to see if the change is real, We investigate the timing properties of B0540-69 using recent ~1000-days Swift satellite data.

• 천문학회지
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• 제36권3호
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• pp.177-187
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• 2003

Active galactic nuclei (AGNs) are distant, powerful sources of radiation over the entire electromagnetic spectrum, from radio waves to gamma-rays. There is much evidence that they are driven by gravitational accretion of stars, dust, and gas, onto central massive black holes (MBHs) imprisoning anywhere from $\~$1 to $\~$10,000 million solar masses; such objects may naturally form in the centers of galaxies during their normal dynamical evolution. A small fraction of AGNs, of the radio-loud type (RLAGNs), are somehow able to generate powerful synchrotron-emitting structures (cores, jets, lobes) with sizes ranging from pc to Mpc. A brief summary of AGN observations and theories is given, with an emphasis on RLAGNs. Preliminary results from the imaging of 10000 extragalactic radio sources observed in the MITVLA snapshot survey, and from a new analytic theory of the time-variable power output from Kerr black hole magnetospheres, are presented. To better understand the complex physical processes within the central engines of AGNs, it is important to confront the observations with theories, from the viewpoint of analyzing the time-variable behaviours of AGNs - which have been recorded over both 'short' human ($10^0-10^9\;s$) and 'long' cosmic ($10^{13} - 10^{17}\;s$) timescales. Some key ingredients of a basic mathematical formalism are outlined, which may help in building detailed Monte-Carlo models of evolving AGN populations; such numerical calculations should be potentially important tools for useful interpretation of the large amounts of statistical data now publicly available for both AGNs and RLAGNs.