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	再電離期 21cm 線	パルサータイミングアレイ
分野	天文学	天文学
系統	Process / pipeline	Process / pipeline
提唱年	1990	1979
提唱者	David Scott	Stephen Detweiler
種類	Radio observational method	Observational timing method
原典	Scott, D., & Rees, M. J. (1990). The 21-cm signature of the ionization of the intergalactic medium. Monthly Notices of the Royal Astronomical Society, 247, 510-516.	Sazhin, M. V. (1978). Opportunities for detecting ultralong gravitational waves. Soviet Astronomy, 22, 36-38.
別名	EoR 21-cm, Hydrogen Line Observations, 21-cm Signal Mapping	PTA, Millisecond Pulsar Timing, Pulsar Timing Residuals
関連	3	3
概要	The 21-centimeter line observation of neutral hydrogen is a powerful technique for studying the Epoch of Reionization, when the first stars and galaxies ionized the intergalactic medium about 13 billion years ago. Proposed by Scott and Rees in 1990, this method probes the universe's transition from the dark ages to the cosmic dawn through the characteristic hyperfine line emission of hydrogen.	A pulsar timing array uses multiple millisecond pulsars as a distributed network of gravitational wave detectors across the galaxy. Proposed theoretically by Stephen Detweiler in 1979, this method exploits the extraordinary timing precision of pulsars to detect the subtle spacetime distortions caused by gravitational waves. In 2023, the first evidence for a stochastic background of gravitational waves was announced using pulsar timing arrays.