Editing Physical cosmology (section)

===Gravitational waves===
[[Gravitational wave]]s are ripples in the [[curvature]] of [[spacetime]] that propagate as [[wave]]s at the speed of light, generated in certain gravitational interactions that propagate outward from their source. [[Gravitational-wave astronomy]] is an emerging branch of [[observational astronomy]] which aims to use gravitational waves to collect observational data about sources of detectable gravitational waves such as [[binary star]] systems composed of [[white dwarf]]s, [[neutron star]]s, and [[black hole]]s; and events such as [[supernova]]e, and the formation of the [[chronology of the universe|early universe]] shortly after the Big Bang.<ref name=Colpi2017>{{cite book | chapter=Gravitational Wave Sources in the Era of Multi-Band Gravitational Wave Astronomy | last1=Colpi | first1=Monica | last2=Sesana | first2=Alberto | title=An Overview of Gravitational Waves: Theory, Sources and Detection | editor1-first=Augar | editor1-last=Gerard | editor2-first=Plagnol | editor2-last=Eric | isbn=978-981-314-176-6 | pages=43–140 | year=2017 | doi=10.1142/9789813141766_0002 | bibcode=2017ogw..book...43C | arxiv=1610.05309 | s2cid=119292265 }}</ref>

In 2016, the [[LIGO]] Scientific Collaboration and [[Virgo interferometer|Virgo]] Collaboration teams announced that they had made the [[first observation of gravitational waves]], originating from a [[Binary black hole|pair]] of [[Stellar collision|merging]] black holes using the Advanced LIGO detectors.<ref name="Discovery 2016">{{cite journal |title=Einstein's gravitational waves found at last |journal=Nature News| url=http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |date=11 February 2016 |last1=Castelvecchi |first1=Davide |last2=Witze |first2=Witze |doi=10.1038/nature.2016.19361  |s2cid=182916902|access-date=2016-02-11 }}</ref><ref name="Abbot">{{cite journal |author=Abbott |first=B. P. |display-authors=etal |year=2016 |title=Observation of Gravitational Waves from a Binary Black Hole Merger |journal=Physical Review Letters |volume=116 |issue=6 |pages=061102 |arxiv=1602.03837 |bibcode=2016PhRvL.116f1102A |doi=10.1103/PhysRevLett.116.061102 |pmid=26918975 |s2cid=124959784 |collaboration=LIGO Scientific Collaboration and Virgo Collaboration}}</ref><ref name='NSF'>{{cite web|title = Gravitational waves detected 100 years after Einstein's prediction |publisher=National Science Foundation|url = https://www.nsf.gov/news/news_summ.jsp?cntn_id=137628|website = www.nsf.gov|access-date = 11 February 2016}}</ref> On 15 June 2016, a [[GW151226|second detection]] of gravitational waves from coalescing black holes was announced.<ref name="NYT-20160615">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Scientists Hear a Second Chirp From Colliding Black Holes |url=https://www.nytimes.com/2016/06/16/science/ligo-gravitational-waves-einstein.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2016/06/16/science/ligo-gravitational-waves-einstein.html |archive-date=2022-01-01 |url-access=limited |date=15 June 2016 |work=[[The New York Times]] |access-date=15 June 2016 }}{{cbignore}}</ref> Besides LIGO, many other [[Gravitational-wave observatory|gravitational-wave observatories (detectors)]] are under construction.<ref>{{cite web|title=The Newest Search for Gravitational Waves has Begun|url=https://ligo.caltech.edu/news/ligo20150918|website=LIGO Caltech|publisher=[[LIGO]]|access-date=29 November 2015|date=18 September 2015}}</ref>