Editing General relativity (section)

==== Orbital decay ====
<!--This subsection is linked to from the subsection Gravitational Waves in Astrophysical Applications, please do not change its title -->

[[File:PSRJ0737−3039shift2021.png|thumb|upright=0.8|Orbital decay for PSR J0737−3039: time shift (in [[second|s]]), tracked over 16 years (2021).<ref name=":1">{{Cite journal|last1=Kramer|first1=M.|last2=Stairs|first2=I. H.|last3=Manchester|first3=R. N.|last4=Wex|first4=N.|last5=Deller|first5=A. T.|last6=Coles|first6=W. A.|last7=Ali|first7=M.|last8=Burgay|first8=M.|last9=Camilo|first9=F.|last10=Cognard|first10=I.|last11=Damour|first11=T.|date=13 December 2021|title=Strong-Field Gravity Tests with the Double Pulsar|url=https://link.aps.org/doi/10.1103/PhysRevX.11.041050|journal=Physical Review X|language=en|volume=11|issue=4|page=041050|doi=10.1103/PhysRevX.11.041050|arxiv=2112.06795|bibcode=2021PhRvX..11d1050K|s2cid=245124502|issn=2160-3308}}</ref>]]

According to general relativity, a [[Binary system (astronomy)|binary system]] will emit gravitational waves, thereby losing energy. Due to this loss, the distance between the two orbiting bodies decreases, and so does their orbital period. Within the [[Solar System]] or for ordinary [[double star]]s, the effect is too small to be observable. This is not the case for a close binary pulsar, a system of two orbiting [[neutron star]]s, one of which is a [[pulsar]]: from the pulsar, observers on Earth receive a regular series of radio pulses that can serve as a highly accurate clock, which allows precise measurements of the orbital period. Because neutron stars are immensely compact, significant amounts of energy are emitted in the form of gravitational radiation.<ref>{{Harvnb|Stairs|2003}}, {{Harvnb|Schutz|2003|pp=317–321}}, {{Harvnb|Bartusiak|2000|pp=70–86}}</ref>

The first observation of a decrease in orbital period due to the emission of gravitational waves was made by [[Russell Alan Hulse|Hulse]] and [[Joseph Hooton Taylor, Jr.|Taylor]], using the binary pulsar [[PSR1913+16]] they had discovered in 1974. This was the first detection of gravitational waves, albeit indirect, for which they were awarded the 1993 [[Nobel Prize]] in physics.<ref>{{Harvnb|Weisberg|Taylor|2003}}; for the pulsar discovery, see {{Harvnb|Hulse|Taylor|1975}}; for the initial evidence for gravitational radiation, see {{Harvnb|Taylor|1994}}</ref> Since then, several other binary pulsars have been found, in particular the double pulsar [[PSR J0737−3039]], where both stars are pulsars<ref>{{Harvnb|Kramer|2004}}</ref> and which was last reported to also be in agreement with general relativity in 2021 after 16 years of observations.<ref name=":1" />