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TianQin
Location(s)	outer space
Organization	Sun Yat-sen University
Telescope style	gravitational-wave observatory; interferometer; space telescope
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The TianQin Project (Chinese: 天琴计划) is a proposed space-borne gravitational-wave observatory (gravitational-wave detector) consisting of three spacecraft in Earth orbit. The TianQin project is being led by Professor Luo Jun (Chinese: 罗俊), President of Sun Yat-sen University, and is based in the university's Zhuhai campus. Construction on project-related infrastructure, which will include a research building, ultra-quiet cave laboratory, and observation center, began in March 2016. The project is estimated to cost 15 billion RMB (US$2.3 billion),^[1]^[2]^[3]^[4] with a projected completion date in the mid-2030s.^[5]^[6] In December 2019, China launched Tianqin-1, a technology demonstration.^[7]

The project's name combines the Chinese words "Tianqin" (Chinese: 天琴; pinyin: Tiān qín) - the plucked string musical instrument of Zhuang people in China. This name refers to the metaphorical concept of gravitational waves "plucking the strings" by causing fluctuations in the 100,000 kilometer laser beams stretching between each of the three TianQin spacecraft.

The observatory will consist of three identical drag-free controlled spacecraft in high Earth orbits at an altitude of about 100,000 km. The nominal source of the observatory is a white-dwarf binary RX J0806.3+1527 (also known as HM Cancri).^[8] This could serve as a good calibration source for the TianQin gravitational wave observatory. Similar configuration of geocentric orbit space-borne gravitational wave detectors have been developed since 2011,^[9]^[10] and was shown to have favorable properties for observing intermediate-mass and massive black-hole binaries.^[10]

Apart from Galactic binaries, the TianQin observatory can also detect sources like massive black hole binaries, extreme mass ratio inspirals, stellar-mass black hole binary inspirals, and stochastic gravitational wave background, etc.^[11]

The detection rate for massive black hole binaries is expected to be as high as about 60 per year,^[12] and TianQin would have accurate estimate to the source's parameters,^[13] which enable the potential for distinguishing the seed models for massive black holes, as well as issuing early warning for nearby mergers.^[12] It can also be used to test the no-hair theorem ^[14] or constrain modified gravity.^[15]

References

^ Jun Luo; et al. (2016). "TianQin: a space-borne gravitational wave detector". Classical and Quantum Gravity. 33 (3): 035010. arXiv:1512.02076. Bibcode:2016CQGra..33c5010L. doi:10.1088/0264-9381/33/3/035010. S2CID 54833657.
^ Jianwei Mei; Chenggang Shao; Yan Wang (2015). Fundamentals of the TianQin mission. XIIth International Conference on Gravitation, Astrophysics and Cosmology, PFUR, Moscow, Russia, 2015-07. arXiv:1510.04754. Bibcode:2016gac..conf..360M. doi:10.1142/9789814759816_0079. Archived 2018-04-11 at the Wayback Machine. proceedings not yet published as of 2015-12.
^ Hsien-Chi Yeh. (2015). Current progress of developing inter-satellite laser interferometry for TIANQIN missions. XIIth International Conference on Gravitation, Astrophysics and Cosmology, PFUR, Moscow, Russia, 2015-07. Archived 2018-04-11 at the Wayback Machine. proceedings not yet published as of 2015-12.
^ J. Luo; J. Mei; H.-C. Yeh; C. Shao; M.V. Sazhin; V. Milyukov. (2015). TIANQIN mission concept. XIIth International Conference on Gravitation, Astrophysics and Cosmology, PFUR, Moscow, Russia, 2015-07. Archived 2018-04-11 at the Wayback Machine. proceedings not yet published as of 2015-12.
^ ZHOU WENTING (2019-04-12). "China-led project expected to enhance space research". China Daily. Retrieved 2019-09-19.
^ Hu, Yiming; Mei, Jianwei; Luo, Jun (1 August 2019). "TianQin project and international collaboration". Chinese Science Bulletin. 64 (24): 2475–2483. doi:10.1360/N972019-00046.
^ "China launches first satellite for space-based gravitational wave detection". New China TV. 2019-12-21. Retrieved 2019-12-21.
^ Ye, Bo-Bing; Zhang, Xuefeng; Zhou, Ming-Yue; et al. (2019). "Optimizing orbits for TianQin". International Journal of Modern Physics D. 28 (9): 1950121. arXiv:2012.03260. Bibcode:2019IJMPD..2850121Y. doi:10.1142/S0218271819501219. S2CID 145846821.
^ Massimo Tinto; J. C. N. de Araujo; Odylio D. Aguiar; Eduardo da Silva Alves (2012). A Geostationary Gravitational Wave Interferometer (GEOGRAWI). Concepts for the NASA Gravitational-Wave Mission, Solicitation: NNH11ZDA019L. arXiv:1111.2576.
^ ^a ^b Sean T. McWilliams (2012). Geostationary Antenna for Disturbance-Free Laser Interferometry (GADFLI). Concepts for the NASA Gravitational-Wave Mission, Solicitation: NNH11ZDA019L. arXiv:1111.3708.
^ Hu, Yi-Ming; Mei, Jianwei; Luo, Jun (September 2017). "Science prospects for space-borne gravitational-wave missions". National Science Review. 4 (5): 683–684. doi:10.1093/nsr/nwx115.
^ ^a ^b Wang, Hai-Tian; Jiang, Zhen; Sesana, Alberto; Barausse, Enrico; Huang, Shun-Jia; Wang, Yi-Fan; Feng, Wen-Fan; Wang, Yan; Hu, Yi-Ming; Mei, Jianwei; Luo, Jun (6 August 2019). "Science with the TianQin observatory: Preliminary results on massive black hole binaries". Physical Review D. 100 (4): 043003. arXiv:1902.04423. Bibcode:2019PhRvD.100d3003W. doi:10.1103/PhysRevD.100.043003. S2CID 118954251.
^ Feng, Wen-Fan; Wang, Hai-Tian; Hu, Xin-Chun; Hu, Yi-Ming; Wang, Yan (5 June 2019). "Preliminary study on parameter estimation accuracy of supermassive black hole binary inspirals for TianQin". Physical Review D. 99 (12): 123002. arXiv:1901.02159. Bibcode:2019PhRvD..99l3002F. doi:10.1103/PhysRevD.99.123002. S2CID 119083959.
^ Shi, Changfu; Bao, Jiahui; Wang, Hai-Tian; Zhang, Jian-dong; Hu, Yi-Ming; Sesana, Alberto; Barausse, Enrico; Mei, Jianwei; Luo, Jun (20 August 2019). "Science with the TianQin observatory: Preliminary results on testing the no-hair theorem with ringdown signals". Physical Review D. 100 (4): 044036. arXiv:1902.08922. Bibcode:2019PhRvD.100d4036S. doi:10.1103/PhysRevD.100.044036. S2CID 119084661.
^ Bao, Jiahui; Shi, Changfu; Wang, Haitian; Zhang, Jian-dong; Hu, Yiming; Mei, Jianwei; Luo, Jun (14 October 2019). "Constraining modified gravity with ringdown signals: an explicit example". Phys. Rev. D. 100 (8). 084024. arXiv:1905.11674. Bibcode:2019PhRvD.100h4024B. doi:10.1103/PhysRevD.100.084024. S2CID 167217249.