Cygnus X-1: Difference between revisions

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
← Previous edit
VisualWikitext
imported>GreenC bot
imported>Oshwah
m Reverted edits by 66.44.74.156 (talk) (HG) (3.4.13)
 
(One intermediate revision by one other user not shown)
Line 20: Line 20:
| ra={{RA|19|58|21.67574}}<ref name=GaiaDR3/>
| ra={{RA|19|58|21.67574}}<ref name=GaiaDR3/>
| dec={{DEC|+35|12|05.7845}}<ref name=GaiaDR3/>
| dec={{DEC|+35|12|05.7845}}<ref name=GaiaDR3/>
| appmag_v=8.95<ref name=SIMBAD/>
| appmag_v=8.72 - 8.93<ref name=gcvs/>
}}
}}
{{Starbox character
{{Starbox character
Line 26: Line 26:
| b-v=+0.81<ref name=lob647/>
| b-v=+0.81<ref name=lob647/>
| u-b=−0.30<ref name=lob647/>
| u-b=−0.30<ref name=lob647/>
| variable=[[Ellipsoidal variable]]
| variable=[[Ellipsoidal variable]]<ref name=gcvs/>
}}
}}
{{Starbox astrometry
{{Starbox astrometry
Line 40: Line 40:
{{Starbox detail
{{Starbox detail
  | source = <ref name=Ramachandran2025/>
  | source = <ref name=Ramachandran2025/>
  |component1=Cygnus X-1
  |component1=Black hole
  | mass=13.8 to {{val|17.5|2.0|1.0}}
  | mass=13.8 to {{val|17.5|2.0|1.0}}
}}
}}
{{Starbox detail|no_heading=y
{{Starbox detail|no_heading=y
| component1=HDE 226868
| component1=Supergiant
| mass = {{val|29|6|3}}
| mass = {{val|29|6|3}}
| radius={{val|22.9|1.5|2.5}}
| radius={{val|22.9|1.5|2.5}}
Line 62: Line 62:
{{Starbox end}}
{{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''' (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/>
Cygnus&nbsp;X-1 is 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]].<ref name=ziolkowski2014/> The supergiant and black hole are separated by 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/>
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/>
Cygnus&nbsp;X-1 was the subject of a [[Thorne–Hawking–Preskill bet#Earlier Thorne–Hawking bet|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/>


==Discovery and observation==
==Discovery and observation==
Line 87: Line 87:


==Binary system==
==Binary system==
The [[black hole]] and [[blue supergiant]] star form a [[binary star|binary system]] in which they orbit around their [[center of mass]] every 5.599829 days.<ref name=aaa343_861/> From the perspective of Earth, the compact object never goes behind the other star; in other words, the system does not [[eclipse]]. However, the [[orbital inclination|inclination of the orbital plane]] to the [[Line-of-sight propagation|line of sight]] from Earth remains uncertain, with predictions ranging from 27° to 65°. A 2007 study estimated the inclination as {{val|48.0|6.8|s=°}}, which would mean that the [[semi-major axis]] is about {{val|0.2|u=[[Astronomical Unit|AU]]}}, or 20% of the distance from Earth to the Sun. The [[orbital eccentricity]] is thought to be only {{val|0.018|0.002}}, meaning a nearly circular orbit.<ref name=orosz2011/><ref name=apj200/> The system is expected to merge into a single [[black hole]] in five billion years, possibly generating [[gravitational wave]]s during the proccess.<ref name=Ramachandran2025/>
The [[black hole]] and [[blue supergiant]] star form a [[binary star|binary system]] in which they orbit around their [[center of mass]] every 5.599829 days.<ref name=aaa343_861/> From the perspective of Earth, the compact object never goes behind the other star; in other words, the system does not [[eclipse]]. However, the [[orbital inclination|inclination of the orbital plane]] to the [[Line-of-sight propagation|line of sight]] from Earth remains uncertain, with predictions ranging from 27° to 65°. A 2007 study estimated the inclination as {{val|48.0|6.8|s=°}}, which would mean that the [[semi-major axis]] is about {{val|0.2|u=[[Astronomical Unit|AU]]}}, or 20% of the distance from Earth to the Sun. The [[orbital eccentricity]] is thought to be only {{val|0.018|0.002}}, meaning a nearly circular orbit.<ref name=orosz2011/><ref name=apj200/> The system is expected to merge into a single [[black hole]] in five billion years, possibly generating [[gravitational wave]]s during the process.<ref name=Ramachandran2025/>


[[File:V1357CygLightCurve.png|thumb|right|A [[Photometric_system#Photometric_letters|blue-band]] [[light curve]] for Cygnus X-1, adapted from Kemp ''et al.'' (1987)<ref name="Kemp"/>]]
[[File:V1357CygLightCurve.png|thumb|right|A [[Photometric_system#Photometric_letters|blue-band]] [[light curve]] for Cygnus X-1, adapted from Kemp ''et al.'' (1987)<ref name="Kemp"/>]]
Line 147: Line 147:
==Stephen Hawking and Kip Thorne==
==Stephen Hawking and Kip Thorne==
[[File:2259 Black Hole 1280 English.jpg|thumb|NASA's "Galaxy of Horrors" poster for Cygnus X-1<ref name=devoured/>]]
[[File:2259 Black Hole 1280 English.jpg|thumb|NASA's "Galaxy of Horrors" poster for Cygnus X-1<ref name=devoured/>]]
Cygnus&nbsp;X-1 was the subject of a bet between physicists [[Stephen Hawking]] and [[Kip Thorne]], in which Hawking bet against the existence of black holes in the region. Hawking later described this as an "insurance policy" of sorts. In his book ''A Brief History of Time'' he wrote:<ref name=hawking1988/>
Cygnus&nbsp;X-1 was the subject of a [[Thorne–Hawking–Preskill bet#Earlier Thorne–Hawking bet|bet]] between physicists [[Stephen Hawking]] and [[Kip Thorne]], in which Hawking bet against the existence of black holes in the region. Hawking later described this as an "insurance policy" of sorts. In his book ''A Brief History of Time'' he wrote:<ref name=hawking1988/>
{{bquote|This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine ''[[Private Eye]]''. If black holes do exist, Kip will get one year of ''[[Penthouse (magazine)|Penthouse]]''. When we made the bet in 1975, we were 80% certain that Cygnus&nbsp;X-1 was a black hole. By now [1988], I would say that we are about 95% certain, but the bet has yet to be settled.}}
{{bquote|This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine ''[[Private Eye]]''. If black holes do exist, Kip will get one year of ''[[Penthouse (magazine)|Penthouse]]''. When we made the bet in 1975, we were 80% certain that Cygnus&nbsp;X-1 was a black hole. By now [1988], I would say that we are about 95% certain, but the bet has yet to be settled.}}
According to the updated tenth-anniversary edition of ''A Brief History of Time'', Hawking has conceded the bet<ref name=hawking1998/> due to subsequent observational data in favor of black holes. In his own book ''[[Black Holes and Time Warps]]'', Thorne reports that Hawking conceded the bet by breaking into Thorne's office while he was in [[Russia]], finding the framed bet, and signing it.<ref name=thorne1994/> While Hawking referred to the bet as taking place in 1975, the written bet itself (in Thorne's handwriting, with his and Hawking's signatures) bears additional witness signatures under a legend stating "Witnessed this tenth day of December 1974".<ref name=wager/> This date was confirmed by Kip Thorne on the January&nbsp;10, 2018 episode of [[Nova (American TV series)|''Nova'']] on [[PBS]].<ref name=apocalypse/>
According to the updated tenth-anniversary edition of ''A Brief History of Time'', Hawking has conceded the bet<ref name=hawking1998/> due to subsequent observational data in favor of black holes. In his own book ''[[Black Holes and Time Warps]]'', Thorne reports that Hawking conceded the bet by breaking into Thorne's office while he was in [[Russia]], finding the framed bet, and signing it.<ref name=thorne1994/> While Hawking referred to the bet as taking place in 1975, the written bet itself (in Thorne's handwriting, with his and Hawking's signatures) bears additional witness signatures under a legend stating "Witnessed this tenth day of December 1974".<ref name=wager/> This date was confirmed by Kip Thorne on the January&nbsp;10, 2018 episode of [[Nova (American TV series)|''Nova'']] on [[PBS]].<ref name=apocalypse/>
Line 155: Line 155:


In the 1979 Disney live-action science fiction film ''[[The Black Hole (1979 film)|The Black Hole]]'', the scientific survey ship captained by Dr. Hans Reinhardt to study the black hole of the film's title is the ''Cygnus'', presumably (although never stated as such) named for the first-identified black hole, Cygnus X-1.<ref name=essays/>
In the 1979 Disney live-action science fiction film ''[[The Black Hole (1979 film)|The Black Hole]]'', the scientific survey ship captained by Dr. Hans Reinhardt to study the black hole of the film's title is the ''Cygnus'', presumably (although never stated as such) named for the first-identified black hole, Cygnus X-1.<ref name=essays/>
Season 7 Episode 10 of Futurama opens with the tagline ''What Happens in Cygnus X-1 Stays In Cygnus X-1.''


== See also ==
== See also ==
Line 169: Line 171:


<ref name=constellation>{{cite constellation|Cygnus X-1}}</ref>
<ref name=constellation>{{cite constellation|Cygnus X-1}}</ref>
<ref name=gcvs>{{cite journal
| title=General Catalogue of Variable Stars
| display-authors=1 | last1=Samus | first1=N. N.
| last2=Kazarovets | first2=E. V. | last3=Durlevich | first3=O. V.
| last4=Kireeva | first4=N. N. | last5=Pastukhova | first5=E. N.
| version=5.1 | journal=Astronomy Reports
| date=2017 | volume=61 | issue=1 | pages=80–88
| doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=255195566 }}</ref>


<ref name="NYT-20210218">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=A Famous Black Hole Gets a Massive Update – Cygnus X-1, one of the first identified black holes, is much weightier than expected, raising new questions about how such objects form |url=https://www.nytimes.com/2021/02/18/science/cygnus-black-hole-astronomy.html
<ref name="NYT-20210218">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=A Famous Black Hole Gets a Massive Update – Cygnus X-1, one of the first identified black holes, is much weightier than expected, raising new questions about how such objects form |url=https://www.nytimes.com/2021/02/18/science/cygnus-black-hole-astronomy.html
Line 181: Line 192:
<ref name=lob647>{{cite journal | last1=Bregman | first1=J. | last2=Butler | first2=D. | last3=Kemper | first3=E. | last4=Koski | first4=A. | last5=Kraft | first5=R. P. | last6=Stone | first6=R. P. S. | title=Colors, magnitudes, spectral types and distances for stars in the field of the X-ray source Cyg&nbsp;X-1 | journal=Lick Observatory Bulletin | date=1973 | pages=1 | volume=647 | bibcode=1973LicOB..24....1B }}</ref>
<ref name=lob647>{{cite journal | last1=Bregman | first1=J. | last2=Butler | first2=D. | last3=Kemper | first3=E. | last4=Koski | first4=A. | last5=Kraft | first5=R. P. | last6=Stone | first6=R. P. S. | title=Colors, magnitudes, spectral types and distances for stars in the field of the X-ray source Cyg&nbsp;X-1 | journal=Lick Observatory Bulletin | date=1973 | pages=1 | volume=647 | bibcode=1973LicOB..24....1B }}</ref>


<ref name=Ramachandran2025>{{Cite journal |last=Ramachandran |first=V. |last2=Sander |first2=A. a. C. |last3=Oskinova |first3=L. M. |last4=Schösser |first4=E. C. |last5=Pauli |first5=D. |last6=Hamann |first6=W.-R. |last7=Mahy |first7=L. |last8=Bernini-Peron |first8=M. |last9=Brigitte |first9=M. |last10=Kubátová |first10=B. |title=Comprehensive UV and optical spectral analysis of Cygnus X-1 - Stellar and wind parameters, abundances, and evolutionary implications |journal=Astronomy & Astrophysics |language=en |volume=698 |pages=A37 |doi=10.1051/0004-6361/202554184 |date=2025-04-08 |arxiv=2504.05885 |issn=0004-6361}}</ref>
<ref name=Ramachandran2025>{{Cite journal |last1=Ramachandran |first1=V. |last2=Sander |first2=A. a. C. |last3=Oskinova |first3=L. M. |last4=Schösser |first4=E. C. |last5=Pauli |first5=D. |last6=Hamann |first6=W.-R. |last7=Mahy |first7=L. |last8=Bernini-Peron |first8=M. |last9=Brigitte |first9=M. |last10=Kubátová |first10=B. |title=Comprehensive UV and optical spectral analysis of Cygnus X-1 - Stellar and wind parameters, abundances, and evolutionary implications |journal=Astronomy & Astrophysics |language=en |volume=698 |pages=A37 |doi=10.1051/0004-6361/202554184 |date=2025-04-08 |arxiv=2504.05885 |bibcode=2025A&A...698A..37R |issn=0004-6361}}</ref>


<ref name=apj321>{{cite journal | last1=Ninkov | first1=Z. | last2=Walker | first2=G. A. H. | last3=Yang | first3=S. | title=The primary orbit and the absorption lines of HDE&nbsp;226868 (Cygnus&nbsp;X-1) | journal=Astrophysical Journal | date=1987 | volume=321 | pages=425–437 | bibcode=1987ApJ...321..425N | doi=10.1086/165641 | url=http://scholarworks.rit.edu/cgi/viewcontent.cgi?article=2310&context=article | access-date=2018-11-04 | archive-url=https://web.archive.org/web/20170922020837/http://scholarworks.rit.edu/cgi/viewcontent.cgi?article=2310&context=article | archive-date=2017-09-22 | url-status=dead }}</ref>
<ref name=apj321>{{cite journal | last1=Ninkov | first1=Z. | last2=Walker | first2=G. A. H. | last3=Yang | first3=S. | title=The primary orbit and the absorption lines of HDE&nbsp;226868 (Cygnus&nbsp;X-1) | journal=Astrophysical Journal | date=1987 | volume=321 | pages=425–437 | bibcode=1987ApJ...321..425N | doi=10.1086/165641 | url=http://scholarworks.rit.edu/cgi/viewcontent.cgi?article=2310&context=article | access-date=2018-11-04 | archive-url=https://web.archive.org/web/20170922020837/http://scholarworks.rit.edu/cgi/viewcontent.cgi?article=2310&context=article | archive-date=2017-09-22 | url-status=dead }}</ref>
Line 221: Line 232:
<ref name=nature235_2_271>{{cite journal | last=Bolton | first=C. T. | date=1972 | title=Identification of Cygnus&nbsp;X-1 with HDE&nbsp;226868 | journal=Nature | volume=235 | issue=5336 | pages=271–273 | doi=10.1038/235271b0 | bibcode = 1972Natur.235..271B | s2cid=4222070 }}</ref>
<ref name=nature235_2_271>{{cite journal | last=Bolton | first=C. T. | date=1972 | title=Identification of Cygnus&nbsp;X-1 with HDE&nbsp;226868 | journal=Nature | volume=235 | issue=5336 | pages=271–273 | doi=10.1038/235271b0 | bibcode = 1972Natur.235..271B | s2cid=4222070 }}</ref>


<ref name=luminet1992>{{cite web | first=Jean-Pierre | last=Luminet | date=1992 | title=Black Holes | publisher=Cambridge University Press | isbn=0-521-40906-3 | url-access=registration | url=https://archive.org/details/blackholes0000lumi }}</ref>
<ref name=luminet1992>{{cite book | first=Jean-Pierre | last=Luminet | date=1992 | title=Black Holes | publisher=Cambridge University Press | isbn=0-521-40906-3 | url-access=registration | url=https://archive.org/details/blackholes0000lumi }}</ref>


<ref name=aaa305_871>{{cite journal | last=Bombaci | first=I. | title=The maximum mass of a neutron star | journal=Astronomy and Astrophysics | date=1996 | volume=305 | pages=871–877 | bibcode=1996A&A...305..871B | arxiv=astro-ph/9608059 | doi=10.1086/310296 | s2cid=119085893 }}</ref>
<ref name=aaa305_871>{{cite journal | last=Bombaci | first=I. | title=The maximum mass of a neutron star | journal=Astronomy and Astrophysics | date=1996 | volume=305 | pages=871–877 | bibcode=1996A&A...305..871B | arxiv=astro-ph/9608059 | doi=10.1086/310296 | s2cid=119085893 }}</ref>
Line 259: Line 270:
<ref name=mgmgr10>{{cite journal |bibcode=2006tmgm.meet.1296M |title=Relativistic Iron Lines in Galactic Black Holes:. Recent Results and Lines in the ASCA Archive |last1=Miller |first1=Jon M. |last2=Fabian |first2=Andrew C. |last3=Nowak |first3=Michael A. |last4=Lewin |first4=Walter H. G. |journal=The Tenth Marcel Grossmann Meeting. On Recent Developments in Theoretical and Experimental General Relativity |date=2006 |page=1296 |doi=10.1142/9789812704030_0093 |arxiv=astro-ph/0402101 |isbn=978-981-256-667-6 }}</ref>
<ref name=mgmgr10>{{cite journal |bibcode=2006tmgm.meet.1296M |title=Relativistic Iron Lines in Galactic Black Holes:. Recent Results and Lines in the ASCA Archive |last1=Miller |first1=Jon M. |last2=Fabian |first2=Andrew C. |last3=Nowak |first3=Michael A. |last4=Lewin |first4=Walter H. G. |journal=The Tenth Marcel Grossmann Meeting. On Recent Developments in Theoretical and Experimental General Relativity |date=2006 |page=1296 |doi=10.1142/9789812704030_0093 |arxiv=astro-ph/0402101 |isbn=978-981-256-667-6 }}</ref>


<ref name=roy_watzke2003>{{cite web | last1=Roy | first1=Steve | last2=Watzke | first2=Megan | date=September 17, 2003 | title="Iron-Clad" Evidence For Spinning Black Hole | journal=Chandra Press Release | page=21 | publisher=Chandra press Room | bibcode=2003cxo..pres...21. | url=http://chandra.harvard.edu/press/03_releases/press_091703.html | access-date=2008-03-11 }}</ref>
<ref name=roy_watzke2003>{{cite journal | last1=Roy | first1=Steve | last2=Watzke | first2=Megan | date=September 17, 2003 | title="Iron-Clad" Evidence For Spinning Black Hole | journal=Chandra Press Release | page=21 | publisher=Chandra press Room | bibcode=2003cxo..pres...21. | url=http://chandra.harvard.edu/press/03_releases/press_091703.html | access-date=2008-03-11 }}</ref>


<ref name=mnras341_2_385>{{cite journal | last1=Podsiadlowski | first1=Philipp | last2=Saul | first2=Rappaport | last3=Han | first3=Zhanwen | title=On the forme web and evolution of black-hole binaries | journal=Monthly Notices of the Royal Astronomical Society | year=2003 | issue=2 | volume=341 | pages=385–404 | arxiv=astro-ph/0207153 | doi=10.1046/j.1365-8711.2003.06464.x | doi-access=free | bibcode = 2003MNRAS.341..385P | s2cid=119476943 }}</ref>
<ref name=mnras341_2_385>{{cite journal | last1=Podsiadlowski | first1=Philipp | last2=Saul | first2=Rappaport | last3=Han | first3=Zhanwen | title=On the forme web and evolution of black-hole binaries | journal=Monthly Notices of the Royal Astronomical Society | year=2003 | issue=2 | volume=341 | pages=385–404 | arxiv=astro-ph/0207153 | doi=10.1046/j.1365-8711.2003.06464.x | doi-access=free | bibcode = 2003MNRAS.341..385P | s2cid=119476943 }}</ref>

Latest revision as of 21:34, 9 September 2025

Template:Short description Script error: No such module "other uses". Template:Sky Template:Main other

Cygnus X-1
Template:Location mark
Location of Cygnus X-1 (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus[1]
Right ascension Template:RA[2]
Declination Template:DEC[2]
Apparent magnitude (V) 8.72 - 8.93[3]
Characteristics
Spectral type O9.7Iab[4]
U−B Template:Engvar −0.30[5]
B−V Template:Engvar +0.81[5]
Variable type Ellipsoidal variable[3]
Astrometry
Radial velocity (Rv)Template:Val[4] km/s
Proper motion (μ) RA: Template:Val mas/yr[2]
Dec.: Template:Val mas/yr[2]
Parallax (π)0.4439±0.0159 mas[2]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)Template:Val[6]
Details[7]
Black hole
Mass13.8 to Template:Val Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Supergiant
MassTemplate:Val Template:Solar mass
RadiusTemplate:Val Template:Solar radius
LuminosityTemplate:Val Template:Solar luminosity
Surface gravity (log g)Template:Val cgs
TemperatureTemplate:Val K
Age4.8-7.6[8] Myr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[4]
Database references
SIMBADdata

Script error: No such module "Check for unknown parameters".

Cygnus X-1 (abbreviated Cyg X-1)[9] is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole.[10][11] It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources detectable from Earth, producing a peak X-ray flux density of Template:Val (Template:Val).[12][13] It remains among the most studied astronomical objects in its class. The compact object is now estimated to have a mass about 21.2 times the mass of the Sun[14][15] and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole.[16] If so, the radius of its event horizon has Template:Val "as upper bound to the linear dimension of the source region" of occasional X-ray bursts lasting only for about 1 ms.[17]

Cygnus X-1 is a high-mass X-ray binary system located about 7,000 light-years away,[14] that includes a blue supergiant variable star.[18] The supergiant and black hole are separated by about 0.2 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.[19] Matter in the inner disk is heated to millions of degrees, generating the observed X-rays.[20][21] A pair of relativistic jets, arranged perpendicularly to the disk, are carrying part of the energy of the infalling material away into interstellar space.[22]

This system may belong to a stellar association called Cygnus OB3, which would mean that Cygnus X-1 is about 5 million years old and formed from a progenitor star that had more than Template:Val. 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.[23]

Cygnus 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.[24] Hawking conceded the bet in 1990 after observational data had strengthened the case that there was indeed a black hole in the system.[25]

Discovery and observation

Observation of X-ray emissions allows astronomers to study celestial phenomena involving gas with temperatures in the millions of degrees. However, because X-ray emissions are blocked by Earth's atmosphere, observation of celestial X-ray sources is not possible without lifting instruments to altitudes where the X-rays can penetrate.[26][27] Cygnus X-1 was discovered using X-ray instruments that were carried aloft by a sounding rocket launched from White Sands Missile Range in New Mexico. As part of an ongoing effort to map these sources, a survey was conducted in 1964 using two Aerobee suborbital rockets. The rockets carried Geiger counters to measure X-ray emission in wavelength range 1–Template:Val across an 8.4° section of the sky. These instruments swept across the sky as the rockets rotated, producing a map of closely spaced scans.[9]

As a result of these surveys, eight new sources of cosmic X-rays were discovered, including Cyg XR-1 (later Cyg X-1) in the constellation Cygnus. The celestial coordinates of this source were estimated as right ascension 19h53m and declination 34.6°. It was not associated with any especially prominent radio or optical source at that position.[9]

Seeing a need for longer-duration studies, in 1963 Riccardo Giacconi and Herb Gursky proposed the first orbital satellite to study X-ray sources. NASA launched their Uhuru satellite in 1970,[28] which led to the discovery of 300 new X-ray sources.[29] Extended Uhuru observations of Cygnus X-1 showed fluctuations in the X-ray intensity that occurs several times a second.[30] This rapid variation meant that the X-ray generation must occur over a compact region no larger than ~Template:Val (roughly the size of Jupiter),[31] as the speed of light restricts communication between more distant regions.

In April–May 1971, Luc Braes and George K. Miley from Leiden Observatory, and independently Robert M. Hjellming and Campbell Wade at the National Radio Astronomy Observatory,[32] detected radio emission from Cygnus X-1, and their accurate radio position pinpointed the X-ray source to the star AGK2 +35 1910 = HDE 226868.[33][34] On the celestial sphere, this star lies about half a degree from the 4th-magnitude star Eta Cygni.[35] It is a supergiant star that is by itself incapable of emitting the observed quantities of X-rays. Hence, the star must have a companion that could heat gas to the millions of degrees needed to produce the radiation source for Cygnus X-1.

Louise Webster and Paul Murdin, at the Royal Greenwich Observatory,[36] and Charles Thomas Bolton, working independently at the University of Toronto's David Dunlap Observatory,[37] announced the discovery of a massive hidden companion to HDE 226868 in 1972. Measurements of the Doppler shift of the star's spectrum demonstrated the companion's presence and allowed its mass to be estimated from the orbital parameters.[38] Based on the high predicted mass of the object, they surmised that it may be a black hole, as the largest possible neutron star cannot exceed three times the mass of the Sun.[39]

With further observations strengthening the evidence, by the end of 1973 the astronomical community generally conceded that Cygnus X-1 was most likely a black hole.[40][41] More precise measurements of Cygnus X-1 demonstrated variability down to a single millisecond. This interval is consistent with turbulence in a disk of accreted matter surrounding a black hole—the accretion disk. X-ray bursts that last for about a third of a second match the expected time frame of matter falling toward a black hole.[42]

File:Cygnus x1 xray.jpg
X-ray image of Cygnus X-1 taken by a balloon-borne telescope, the High-Energy Replicated Optics (HERO) project

Cygnus X-1 has since been studied extensively using observations by orbiting and ground-based instruments.[4] The similarities between the emissions of X-ray binaries such as HDE 226868/Cygnus X-1 and active galactic nuclei suggests a common mechanism of energy generation involving a black hole, an orbiting accretion disk and associated jets.[43] For this reason, Cygnus X-1 is identified among a class of objects called microquasars; an analog of the quasars, or quasi-stellar radio sources, now known to be distant active galactic nuclei. Scientific studies of binary systems such as HDE 226868/Cygnus X-1 may lead to further insights into the mechanics of active galaxies.[44]

Binary system

The black hole and blue supergiant star form a binary system in which they orbit around their center of mass every 5.599829 days.[45] From the perspective of Earth, the compact object never goes behind the other star; in other words, the system does not eclipse. However, the inclination of the orbital plane to the line of sight from Earth remains uncertain, with predictions ranging from 27° to 65°. A 2007 study estimated the inclination as Template:Val, which would mean that the semi-major axis is about Template:Val, or 20% of the distance from Earth to the Sun. The orbital eccentricity is thought to be only Template:Val, meaning a nearly circular orbit.[46][47] The system is expected to merge into a single black hole in five billion years, possibly generating gravitational waves during the process.[7]

File:V1357CygLightCurve.png
A blue-band light curve for Cygnus X-1, adapted from Kemp et al. (1987)[48]

The HDE 226868/Cygnus X-1 system shares a common motion through space with an association of massive stars named Cygnus OB3, which is roughly 7,000 light-years distant. This implies that HDE 226868, Cygnus X-1 and this OB association may have formed at the same time and location. If so, then the age of the system is about Template:Val. The motion of HDE 226868 with respect to Cygnus OB3 is Template:Val, a typical value for random motion within a stellar association. HDE 226868 is about Template:Val from the center of the association and could have reached that separation in about Template:Val—which roughly agrees with estimated age of the association.[23] The distance to Cyg X-1 is calculated by trigonometric parallax as Template:Convert,[49] and by radio astrometry as Template:Convert.[14]

With a galactic latitude of 4° and galactic longitude 71°,[4] this system lies inward along the same Orion Spur, in which the Sun is located within the Milky Way,[50] near where the spur approaches the Sagittarius Arm. Cygnus X-1 has been described as belonging to the Sagittarius Arm,[51] though the structure of the Milky Way is not well established.

Compact object

From various techniques, the mass of the compact object appears to be greater than the maximum mass for a neutron star. Stellar evolutionary models suggest a mass of Template:Val,[52] while other techniques resulted in 10 solar masses. Measuring periodicities in the X-ray emission near the object yielded a more precise value of Template:Val. In all cases, the object is most likely a black hole[46][53]—a region of space with a gravitational field that is strong enough to prevent the escape of electromagnetic radiation from the interior. The boundary of this region is called the event horizon and has an effective radius called the Schwarzschild radius, which is about Template:Val for Cygnus X-1. Anything (including matter and photons) that passes through this boundary is unable to escape.[54] Measurements published in 2021 yielded an estimated mass of Template:Val.[14][15] A 2025 study estimate a mass of 17.5 solar masses, which may be just an upper limit, with another method yielding Template:Solar mass.[7]

Evidence of just such an event horizon may have been detected in 1992 using ultraviolet (UV) observations with the High Speed Photometer on the Hubble Space Telescope. As self-luminous clumps of matter spiral into a black hole, their radiation is emitted in a series of pulses that are subject to gravitational redshift as the material approaches the horizon. That is, the wavelengths of the radiation steadily increase, as predicted by general relativity. Matter hitting a solid, compact object would emit a final burst of energy, whereas material passing through an event horizon would not. Two such "dying pulse trains" were observed, which is consistent with the existence of a black hole.[55]

File:Chandra image of Cygnus X-1.jpg
Chandra X-ray Observatory image of Cygnus X-1

The spin of the compact object is not yet well determined. Past analysis of data from the space-based Chandra X-ray Observatory suggested that Cygnus X-1 was not rotating to any significant degree.[56][57] However, evidence announced in 2011 suggests that it is rotating extremely rapidly, approximately 790 times per second.[58]

Formation

The largest star in the Cygnus OB3 association has a mass 40 times that of the Sun. As more massive stars evolve more rapidly, this implies that the progenitor star for Cygnus X-1 had more than 40 solar masses. Given the current estimated mass of the black hole, the progenitor star must have lost over 30 solar masses of material. Part of this mass may have been lost to HDE 226868, while the remainder was most likely expelled by a strong stellar wind. The helium enrichment of HDE 226868's outer atmosphere may be evidence for this mass transfer.[59] Possibly the progenitor may have evolved into a Wolf–Rayet star, which ejects a substantial proportion of its atmosphere using just such a powerful stellar wind.[23]

If the progenitor star had exploded as a supernova, then observations of similar objects show that the remnant would most likely have been ejected from the system at a relatively high velocity. As the object remained in orbit, this indicates that the progenitor may have collapsed directly into a black hole without exploding (or at most produced only a relatively modest explosion).[23]

Accretion disk

File:Cygx1 spectrum.jpg
A Chandra X-ray spectrum of Cygnus X-1 showing a characteristic peak near Template:Val due to ionized iron in the accretion disk, but the peak is gravitationally red-shifted, broadened by the Doppler effect, and skewed toward lower energies[60]

The compact object is thought to be orbited by a thin, flat disk of accreting matter known as an accretion disk. This disk is intensely heated by friction between ionized gas in faster-moving inner orbits and that in slower outer ones. It is divided into a hot inner region with a relatively high level of ionization—forming a plasma—and a cooler, less ionized outer region that extends to an estimated 500 times the Schwarzschild radius,[21] or about 15,000 km.

Though highly and erratically variable, Cygnus X-1 is typically the brightest persistent source of hard X-rays—those with energies from about 30 up to several hundred kiloelectronvolts—in the sky.[27] The X-rays are produced as lower-energy photons in the thin inner accretion disk, then given more energy through Compton scattering with very high-temperature electrons in a geometrically thicker, but nearly transparent corona enveloping it, as well as by some further reflection from the surface of the thin disk.[61] An alternative possibility is that the X-rays may be Compton-scattered by the base of a jet instead of a disk corona.[62]

The X-ray emission from Cygnus X-1 can vary in a somewhat repetitive pattern called quasi-periodic oscillations (QPO). The mass of the compact object appears to determine the distance at which the surrounding plasma begins to emit these QPOs, with the emission radius decreasing as the mass decreases. This technique has been used to estimate the mass of Cygnus X-1, providing a cross-check with other mass derivations.[63]

Pulsations with a stable period, similar to those resulting from the spin of a neutron star, have never been seen from Cygnus X-1.[64][65] The pulsations from neutron stars are caused by the neutron star's rotating magnetic field, but the no-hair theorem guarantees that the magnetic field of a black hole is exactly aligned with its rotation axis and thus is static. For example, the X-ray binary V 0332+53 was thought to be a possible black hole until pulsations were found.[66] Cygnus X-1 has also never displayed X-ray bursts similar to those seen from neutron stars.[67] Cygnus X-1 unpredictably changes between two X-ray states, although the X-rays may vary continuously between those states as well. In the most common state, the X-rays are "hard", which means that more of the X-rays have high energy. In the less common state, the X-rays are "soft", with more of the X-rays having lower energy. The soft state also shows greater variability. The hard state is believed to originate in a corona surrounding the inner part of the more opaque accretion disk. The soft state occurs when the disk draws closer to the compact object (possibly as close as Template:Val), accompanied by cooling or ejection of the corona. When a new corona is generated, Cygnus X-1 transitions back to the hard state.[68]

The spectral transition of Cygnus X-1 can be explained using a two-component advective flow solution, as proposed by Chakrabarti and Titarchuk.[69] A hard state is generated by the inverse Comptonisation of seed photons from the Keplarian disk and likewise synchrotron photons produced by the hot electrons in the centrifugal-pressure–supported boundary layer (CENBOL).[70]

The X-ray flux from Cygnus X-1 varies periodically every 5.6 days, especially during superior conjunction when the orbiting objects are most closely aligned with Earth and the compact source is the more distant. This indicates that the emissions are being partially blocked by circumstellar matter, which may be the stellar wind from the star HDE 226868. There is a roughly 300-day periodicity in the emission, which could be caused by the precession of the accretion disk.[71]

Jets

File:Tulip and Cygnus X1.png
The picture shows a curved bow shock structure resulting from the Cygnus X-1 accretion disk jet interacting with a dense interstellar cloud

As accreted matter falls toward the compact object, it loses gravitational potential energy. Part of this released energy is dissipated by jets of particles, aligned perpendicular to the accretion disk, that flow outward with relativistic velocities (that is, the particles are moving at a significant fraction of the speed of light). This pair of jets provide a means for an accretion disk to shed excess energy and angular momentum. They may be created by magnetic fields within the gas that surrounds the compact object.[72]

The Cygnus X-1 jets are inefficient radiators and so release only a small proportion of their energy in the electromagnetic spectrum. That is, they appear "dark". The estimated angle of the jets to the line of sight is 30°, and they may be precessing.[68] One of the jets is colliding with a relatively dense part of the interstellar medium (ISM), forming an energized ring that can be detected by its radio emission. This collision appears to be forming a nebula that has been observed in the optical wavelengths. To produce this nebula, the jet must have an estimated average power of 4–Template:Val, or Template:Val.[73] This is more than 1,000 times the power emitted by the Sun.[74] There is no corresponding ring in the opposite direction because that jet is facing a lower-density region of the ISM.[75]

In 2006, Cygnus X-1 became the first stellar-mass black hole found to display evidence of gamma-ray emission in the very high-energy band, above Template:Val. The signal was observed at the same time as a flare of hard X-rays, suggesting a link between the events. The X-ray flare may have been produced at the base of the jet, while the gamma rays could have been generated where the jet interacts with the stellar wind of HDE 226868.[76]

HDE 226868

File:Cygnus X-1.png
An artist's impression of the HDE 226868–Cygnus X-1 binary system

HDE 226868 is a supergiant star with a spectral class of O9.7 Iab,[4] which is on the borderline between class-O and class-B stars. It has an estimated surface temperature of 31,000 K[77] and mass approximately 20–40 times the mass of the Sun. Based on a stellar evolutionary model, at the estimated distance of 2,000 parsecs, this star may have a radius equal to about 15–17[46] times the solar radius and has approximately 300,000–400,000 times the luminosity of the Sun.[52][78] For comparison, the compact object is estimated to be orbiting HDE 226868 at a distance of about 40 solar radii, or twice the radius of this star.[79]

The surface of HDE 226868 is being tidally distorted by the gravity of the massive companion, forming a tear-drop shape that is further distorted by rotation. This causes the optical brightness of the star to vary by 0.06 magnitudes during each 5.6-day binary orbit, with the minimum magnitude occurring when the system is aligned with the line of sight.[80] The "ellipsoidal" pattern of light variation results from the limb darkening and gravity darkening of the star's surface.[81]

When the spectrum of HDE 226868 is compared to the similar star Alnilam, the former shows an overabundance of helium and an underabundance of carbon in its atmosphere.[82] The ultraviolet and hydrogen-alpha spectral lines of HDE 226868 show profiles similar to the star P Cygni, which indicates that the star is surrounded by a gaseous envelope that is being accelerated away from the star at speeds of about 1,500 km/s.[83][84]

Like other stars of its spectral type, HDE 226868 is thought to be shedding mass in a stellar wind at an estimated rate of Template:Val solar masses per year; or one solar mass every 400,000 years.[85] The gravitational influence of the compact object appears to be reshaping this stellar wind, producing a focused wind geometry rather than a spherically symmetrical wind.[79] X-rays from the region surrounding the compact object heat and ionize this stellar wind. As the object moves through different regions of the stellar wind during its 5.6-day orbit, the UV lines,[86] the radio emission,[87] and the X-rays themselves all vary.[88]

The Roche lobe of HDE 226868 defines the region of space around the star where orbiting material remains gravitationally bound. Material that passes beyond this lobe may fall toward the orbiting companion. This Roche lobe is believed to be close to the surface of HDE 226868 but not overflowing, so the material at the stellar surface is not being stripped away by its companion. However, a significant proportion of the stellar wind emitted by the star is being drawn onto the compact object's accretion disk after passing beyond this lobe.[19]

The gas and dust between Earth and HDE 226868 results in a reduction in the apparent magnitude of the star, as well as a reddening of the hue—red light can more effectively penetrate the dust in the interstellar medium. The estimated value of the interstellar extinction (AV) is 3.3 magnitudes.[89] Without the intervening matter, HDE 226868 would be a fifth-magnitude star,[90] and thus visible to the unaided eye.[91]

Stephen Hawking and Kip Thorne

File:2259 Black Hole 1280 English.jpg
NASA's "Galaxy of Horrors" poster for Cygnus X-1[92]

Cygnus X-1 was the subject of a bet between physicists Stephen Hawking and Kip Thorne, in which Hawking bet against the existence of black holes in the region. Hawking later described this as an "insurance policy" of sorts. In his book A Brief History of Time he wrote:[93] Template:Bquote According to the updated tenth-anniversary edition of A Brief History of Time, Hawking has conceded the bet[94] due to subsequent observational data in favor of black holes. In his own book Black Holes and Time Warps, Thorne reports that Hawking conceded the bet by breaking into Thorne's office while he was in Russia, finding the framed bet, and signing it.[95] While Hawking referred to the bet as taking place in 1975, the written bet itself (in Thorne's handwriting, with his and Hawking's signatures) bears additional witness signatures under a legend stating "Witnessed this tenth day of December 1974".[96] This date was confirmed by Kip Thorne on the January 10, 2018 episode of Nova on PBS.[97]

In popular culture

Cygnus X-1 is the subject of a two-part song series by Canadian progressive rock band Rush. The first part, "Book I: The Voyage", is the last song on the 1977 album A Farewell to Kings. The second part, "Book II: Hemispheres", is the first song on the following 1978 album, Hemispheres. The lyrics describe an explorer aboard the spaceship Rocinante, who travels to the black hole, believing that there may be something beyond it. As he moves closer, it becomes increasingly difficult to control the ship, and he is eventually drawn in by the pull of gravity.[98]

In the 1979 Disney live-action science fiction film The Black Hole, the scientific survey ship captained by Dr. Hans Reinhardt to study the black hole of the film's title is the Cygnus, presumably (although never stated as such) named for the first-identified black hole, Cygnus X-1.[99]

Season 7 Episode 10 of Futurama opens with the tagline What Happens in Cygnus X-1 Stays In Cygnus X-1.

See also

Script error: No such module "Portal".

References

Template:Reflist

External links

Template:Sister project

Template:S-achTemplate:S-endTemplate:Stars of CygnusTemplate:Portal bar
Preceded byTemplate:S-bef/check Least distant black hole
1972—1986 Template:S-ttl/check 		Template:S-aft/check Succeeded by
  1. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named constellation
  2. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named GaiaDR3
  3. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named gcvs
  4. ↑ a b c d e f Cite error: Invalid <ref> tag; no text was provided for refs named SIMBAD
  5. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named lob647
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj321
  7. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named Ramachandran2025
  8. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wong2012
  9. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named science3656
  10. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named esa20041105
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named glister2011
  12. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lewin_vanderklis2006
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named usno2010
  14. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named SCI-20210218
  15. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named NYT-20210218
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named encyclopedia
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named harko20060628
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named ziolkowski2014
  19. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named apj304_371
  20. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nayashin_dove1998
  21. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named mnras325_3_1045
  22. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mdsai76_600
  23. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named science300_5622_1119
  24. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named episode
  25. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named su20040227
  26. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named herbert2002
  27. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named apj611_2_1084
  28. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named heasarc20030626
  29. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named giacconi20021208
  30. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj166_L1
  31. ↑ This is the distance light can travel in a third of a second.
  32. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj168_L91
  33. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nature232_5308_246
  34. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named vrsb9_100_173
  35. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bernard_stecker1999
  36. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nature235_2_37
  37. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nature235_2_271
  38. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named luminet1992
  39. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa305_871
  40. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rolston1997
  41. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apl16_1_9
  42. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj189_77
  43. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mnras372_3_1366
  44. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named brainerd20050720
  45. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa343_861
  46. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named orosz2011
  47. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj200
  48. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Kemp
  49. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj742_2
  50. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj167_L15
  51. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named goebel
  52. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named MNRAS358_3_851
  53. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named esa070516
  54. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mit20060109
  55. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named pasp113
  56. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mgmgr10
  57. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named roy_watzke2003
  58. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rapid rotation
  59. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mnras341_2_385
  60. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named chandra20060830
  61. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj484_1_375
  62. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named asr38_12_2810
  63. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj678_2_1230
  64. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named science297_5583_947
  65. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wen1998
  66. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj2le288_L45
  67. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named ag44_6_77
  68. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named apj626_2_1015
  69. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named CHTI_1
  70. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named CHM_1
  71. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj531_1_546
  72. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named science300_5627
  73. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mnras376_3_1341
  74. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj418_457
  75. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nature436_7052_819
  76. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apjl665_1_L51
  77. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named eas030610
  78. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named iorio2007
  79. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named apj620_1_398
  80. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named caballero
  81. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named cox2001
  82. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rmaa31_1_63
  83. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa63_1
  84. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj506_1_424
  85. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj203_438
  86. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named baas38_334
  87. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named mnras302_1_L1
  88. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj583_1_424
  89. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apj185_2_L113
  90. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named sut_ir
  91. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named kaler
  92. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named devoured
  93. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named hawking1988
  94. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named hawking1998
  95. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named thorne1994
  96. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wager
  97. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named apocalypse
  98. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rush
  99. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named essays
Retrieved from "http://debianws.lexgopc.com/wiki143/index.php?title=Cygnus_X-1&oldid=3244689"