Editing Cygnus X-1 (section)

{{short description|Galactic X-ray source in the constellation Cygnus that is very likely a black hole}}
{{Other uses}}
{{Sky|19|58|21.6756|+|35|12|05.775|6000}}
{{featured article}}
{{Starbox begin
| name=Cygnus X-1}}
{{Starbox image
 | image=
   {{Location mark
     | image=Cygnus IAU.svg
     | float=center | width=250 | position=right
     | mark=Red circle.svg | mark_width=10 | mark_link=Cyg X-1
     | x%=62.0 | y%=61.0
   }}
 | caption=Location of Cygnus X-1 (circled)
}}
{{Starbox observe
| epoch=J2000
| constell=[[Cygnus (constellation)|Cygnus]]<ref name=constellation/>
| ra={{RA|19|58|21.67574}}<ref name=GaiaDR3/>
| dec={{DEC|+35|12|05.7845}}<ref name=GaiaDR3/>
| appmag_v=8.95<ref name=SIMBAD/>
}}
{{Starbox character
| class=O9.7Iab<ref name=SIMBAD/>
| b-v=+0.81<ref name=lob647/>
| u-b=−0.30<ref name=lob647/>
| variable=[[Ellipsoidal variable]]
}}
{{Starbox astrometry
| radial_v={{val|-2.70|3.2}}<ref name=SIMBAD/>
| prop_mo_ra={{val|-3.812|0.015}}
| prop_mo_dec={{val|-6.310|0.017}}
| pm_footnote=<ref name=GaiaDR3/>
| parallax=0.4439
| p_error=0.0159
| parallax_footnote=<ref name=GaiaDR3/>
| absmag_v={{val|-6.5|0.2}}<ref name=apj321/>
}}
{{Starbox detail
 | source = <ref name=Ramachandran2025/>
 |component1=Cygnus X-1
 | mass=13.8 to {{val|17.5|2.0|1.0}}
}}
{{Starbox detail|no_heading=y
| component1=HDE 226868
| mass = {{val|29|6|3}}
| radius={{val|22.9|1.5|2.5}}
| luminosity={{val|320000|82000|65000|fmt=commas}}
| temperature={{val|28500|1000|fmt=commas}}
| gravity={{val|3.17|0.10}}
| metal=
| rotation=
| age_myr=4.8-7.6<ref name=wong2012/>
}}
{{Starbox catalog
| names= {{odlist|V=V1357 Cygni|BD=+34°3815|HD=226868, HDE 226868|HIP=98298|SAO=69181}}<ref name=SIMBAD/>
}}
{{Starbox reference
|Simbad=Cyg+X-1
}}
{{Starbox end}}

'''Cygnus&nbsp;X-1''' (abbreviated '''Cyg&nbsp;X-1''')<ref name=science3656/> is a galactic [[Astrophysical X-ray source|X-ray source]] in the [[constellation]] [[Cygnus (constellation)|Cygnus]] and was the first such source widely accepted to be a [[black hole]].<ref name=esa20041105/><ref name=glister2011/> It was discovered in 1964 during a [[Sub-orbital spaceflight|rocket flight]] and is one of the [[Signal strength|strongest]] X-ray sources detectable from Earth, producing a peak X-ray [[flux density]] of {{val|2.3|e=-23|u=[[Watt|W]]/([[Meter|m]]<sup>2</sup>⋅[[Hertz|Hz]])}} ({{val|2.3|e=3|u=[[jansky]]}}).<!-- Units are taken from the cited source. See the Jansky article before changing. --><ref name=lewin_vanderklis2006/><ref name=usno2010/> It remains among the most studied [[astronomical object]]s in its class. The compact object is now estimated to have a mass about 21.2 times the [[Solar mass|mass of the Sun]]<ref name="SCI-20210218" /><ref name="NYT-20210218" /> and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole.<ref name=encyclopedia/> If so, the radius of its [[event horizon]] has {{val|300|ul=km}} "as upper bound to the linear dimension of the source region" of occasional X-ray bursts lasting only for about 1&nbsp;ms.<ref name=harko20060628/>

Cygnus&nbsp;X-1 belongs to a high-mass [[X-ray binary]] system, located about  7,000 [[light-year]]s away,<ref name="SCI-20210218" /> that includes a blue [[Supergiant star|supergiant]] [[variable star]] designated '''HDE&nbsp;226868''',<ref name=ziolkowski2014/> which it orbits at about 0.2&nbsp;AU, or 20% of the distance from Earth to the Sun. A [[stellar wind]] from the star provides material for an [[accretion disk]] around the X-ray source.<ref name=apj304_371/> Matter in the inner disk is heated to millions of degrees, generating the observed X-rays.<ref name=nayashin_dove1998/><ref name=mnras325_3_1045/> A pair of [[relativistic jet]]s, arranged [[perpendicular]]ly to the disk, are carrying part of the energy of the infalling material away into interstellar space.<ref name=mdsai76_600/>

This system may belong to a [[stellar association]] called Cygnus&nbsp;OB3, which would mean that Cygnus&nbsp;X-1 is about 5&nbsp;million years old and formed from a [[wiktionary:progenitor|progenitor]] star that had more than {{val|40|u=[[solar mass]]es}}. The majority of the star's mass was shed, most likely as a stellar wind. If this star had then exploded as a [[supernova]], the resulting force would most likely have ejected the remnant from the system. Hence the star may have instead collapsed directly into a black hole.<ref name=science300_5622_1119/>

Cygnus&nbsp;X-1 was the subject of a friendly scientific wager between physicists [[Stephen Hawking]] and [[Kip Thorne]] in 1975, with Hawking—betting that it was not a black hole—hoping to lose.<ref name=episode/> Hawking conceded the bet in 1990 after observational data had strengthened the case that there was indeed a [[black hole]] in the system.<ref name=su20040227/>