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| *http://preposterousuniverse.com/grnotes/
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| *:''Triggered by <code>\bpreposterousuniverse\.com\b</code> on the local blacklist''|bot=Cyberbot II}}
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| {{Expand Chinese|引力波天文学|fa=yes|date=July 2012}}
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| [[Image:LIGO control.jpg|thumb|230px|right|The LIGO Hanford Control Room]]
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| '''Gravitational-wave astronomy''' is an emerging branch of [[observational astronomy]] which aims to use [[gravitational waves]] (minute distortions of [[spacetime]] predicted by [[Einstein]]'s theory of [[general relativity]]) to collect observational data about objects such as [[neutron star]]s and [[black hole]]s, about events such as [[supernova]]e and about the early [[universe]] shortly after the [[big bang]]. The Laser Interferometer Gravitational-Wave Observatory or [[LIGO]], a joint project between [[MIT]] and [[Caltech]] is spearheading this new field of research along with equally ambitious projects such as [[Laser Interferometer Space Antenna|LISA]], [[VIRGO]], [[TAMA 300]] and [[GEO 600]].
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| ==Development==
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| So far, gravitational waves have only been detected indirectly, and gravitational-wave astronomy remains more of a possibility than an actuality. However, a number of [[gravitational-wave detector]]s are in operation with the aim of making gravitational-wave astronomy a reality. This young area of research is still in the developmental stages, however there is consensus within the astrophysics community that this field will evolve to become an established component of 21st century multi-messenger astronomy, and that gravitational-wave astronomers, working with ground and spaced-based detectors, will stand shoulder-to-shoulder with gamma-ray, x-ray, optical, infrared and radio astronomers in exploring the cosmos in the years to come.
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| Detecting gravitational waves promises to complement observations in the [[electromagnetic spectrum]]:<ref>Cf. {{Harvnb|Thorne|1995}}.</ref> These waves also promise to yield information in ways not possible via detection and analysis of electromagnetic waves. Electromagnetic waves can be absorbed and re-radiated in ways that make extracting information about the source difficult. Gravitational waves behave, in some analogous to sound waves, in that they behave like composites of harmonic waves.<ref>See {{harvnb|Golm|Postdam|2013|loc=sec. 4}}</ref> These harmonic composite waveforms carry the signature of their origin only and radiate in a way that doesn't allow them to become distorted due to interactions with matter between the source and the detectors.<ref>See {{harvnb|Golm|Postdam|2013|loc=sec. 4}}</ref> This should allow astronomers to view the center of a supernova, stellar nebula's, and even colliding galactic cores in new ways.
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| Terrestrial detectors are expected to yield new information about the inspiral phase and mergers of binary [[stellar black hole|stellar mass black holes]], and binaries consisting of one such black hole and a [[neutron star]] (a candidate mechanism for some [[gamma ray burst]]s). They could also detect signals from [[core-collapse supernova]]e, and from periodic sources such as pulsars with small deformations. If there is truth to speculation about certain kinds of [[phase transition]]s or kink bursts from long [[cosmic string]]s in the very early universe (at [[cosmic time]]s around <math>10^{-25}</math> seconds), these could also be detectable.<ref>See {{Harvnb|Cutler|Thorne|2002|loc=sec. 2}}.</ref> Space-based detectors like LISA should detect objects such as binaries consisting of two [[white dwarfs]], and [[AM CVn star]]s (a [[white dwarf]] accreting matter from its binary partner, a low-mass helium star), and also observe the mergers of [[supermassive black hole]]s and the inspiral of smaller objects (between one and a thousand [[solar mass]]es) into such black holes. LISA should also be able to listen to the same kind of sources from the early universe as ground-based detectors, but at even lower frequencies and with greatly increased sensitivity.<ref>See {{Harvnb|Cutler|Thorne|2002|loc=sec. 3}}.</ref>
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| Detecting emitted gravitational waves are rather difficult endeavor. It involves ultra stable high quality lasers and detectors calibrated with a sensitivity of at least 2·10^(-22)/√Hz as shown at the ground-based detector, GEO-600.<ref>See {{harvnb|Seifert F., et al|2006|loc=sec. 5}}.</ref> It has also been proposed that even from large astronomical events, such as supernova explosions, these waves are likely to degrade to vibrations as small as an atomic diameter.<ref>See {{harvnb|Golm|Postdam|2013|loc=sec. 4}}.</ref> In theory, the high sensitivity of terrestrial and space-based detection systems should be able to observe these elusive waves.
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| ==Notes==
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| {{reflist}}
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| ==References==
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| {{refbegin}}
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| * {{Citation
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| | last1=Cutler
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| | first1=Curt
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| | last2=Thorne
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| | first2=Kip S.
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| | contribution=An overview of gravitational-wave sources
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| | year=2002
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| | title=Proceedings of 16th International Conference on General Relativity and Gravitation (GR16)
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| | editor1-last=Bishop
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| | editor1-first=Nigel
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| | editor2-last=Maharaj
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| | editor2-first=Sunil D.
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| | publisher=World Scientific
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| | isbn=981-238-171-6
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| | arxiv=gr-qc/0204090
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| |bibcode = 2002gr.qc.....4090C
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| | page=4090 }}
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| *{{Citation
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| | author-link=Kip Thorne
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| | last=Thorne
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| | first=Kip S.
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| | year=1995
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| | title=Gravitational radiation
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| | arxiv= gr-qc/9506086
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| |bibcode = 1995pnac.conf..160T
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| | page=160
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| | journal=Particle and Nuclear Astrophysics and Cosmology in the Next Millenium }}
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| *{{citation|ref={{harvid|Golm|Postdam|2013}}
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| |last1=Golm
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| |last2=Postdam
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| |title=Graviational Wave Astronomy
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| |url=http://www.einstein-online.info/elementary/gravWav
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| |publisher=Max Planck Institute for Gravitational Physics
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| |accessdate=24 January 2013
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| }}
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| *{{citation|ref={{harvid|Seifert F., et al|2006}}
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| |author=Seifert F., Kwee P., Heurs M., Willke B, Danzmann K
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| |title = GEO600 Sensetivity
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| |url = http://www.geo600.org/research-highlights/geo600-has-reached-a-sensitivity-of-2b710-22-221ahz-1
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| |year = 2006
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| }}
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| {{refend}}
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| ==External links==
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| * [http://astrogravs.nasa.gov/docs/index.html AstroGravS: Astrophysical Gravitational-Wave Sources Archive]
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| * [http://preposterousuniverse.com/grnotes/ Lecture Notes on General Relativity]
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| * [http://www.astro.cardiff.ac.uk/research/gravity/ Physics Group]
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| * [http://www.geo600.org/general-information LIGO affiliate research center]
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| {{Astronomy navbox}}
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| [[Category:Gravitation]]
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| [[Category:General relativity]]
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| [[Category:Observational astronomy]]
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| [[Category:Astrophysics]]
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| [[Category:Unsolved problems in physics]]
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| {{Link FA|zh}}
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