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Cygnus X-1

For other uses, see Cygnus X-1 (disambiguation).

Cygnus X-1
Location of Cygnus X-1 (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus[1]
Right ascension 19h 58m 21.67574s[2]
Declination +35° 12′ 05.7845″[2]
Apparent magnitude (V) 8.95[3]
Characteristics
Spectral type O9.7Iab[3]
U−B color index −0.30[4]
B−V color index +0.81[4]
Variable type Ellipsoidal variable
Astrometry
Radial velocity (Rv)−2.70±3.2[3] km/s
Proper motion (μ) RA: −3.812±0.015 mas/yr[2]
Dec.: −6.310±0.017 mas/yr[2]
Parallax (π)0.4439±0.0159 mas[2]
Distance7,300 ± 300 ly
(2,250 ± 80 pc)
Absolute magnitude (MV)−6.5±0.2[5]
Details[6]
Cygnus X-1
Mass13.8 to 17.5+2.0
−1.0 M☉
HDE 226868
Mass29+6
−3 M☉
Radius22.9+1.5
−2.5 R☉
Luminosity320,000+82,000
−65,000 L☉
Surface gravity (log g)3.17±0.10 cgs
Temperature28,500±1,000 K
Age4.8-7.6[7] Myr
Other designations
V1357 Cygni, BD+34°3815, HD 226868, HDE 226868, HIP 98298, SAO 69181[3]
Database references
SIMBADdata

Cygnus X-1 (abbreviated Cyg X-1)[8] is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole.[9][10] 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 2.3×10−23 W/(m2⋅Hz) (2.3×103 jansky).[11][12] 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[13][14] and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole.[15] If so, the radius of its event horizon has 300 km "as upper bound to the linear dimension of the source region" of occasional X-ray bursts lasting only for about 1 ms.[16]

Cygnus X-1 belongs to a high-mass X-ray binary system, located about 7,000 light-years away,[13] that includes a blue supergiant variable star designated HDE 226868,[17] which it orbits at 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.[18] Matter in the inner disk is heated to millions of degrees, generating the observed X-rays.[19][20] A pair of relativistic jets, arranged perpendicularly to the disk, are carrying part of the energy of the infalling material away into interstellar space.[21]

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 40 solar masses. 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.[22]

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.[23] Hawking conceded the bet in 1990 after observational data had strengthened the case that there was indeed a black hole in the system. As of 2004, this hypothesis lacked direct empirical evidence but was generally accepted based on indirect evidence.[24]

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  4. ^ a b Cite error: The named reference lob647 was invoked but never defined (see the help page).
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  13. ^ a b Cite error: The named reference SCI-20210218 was invoked but never defined (see the help page).
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  24. ^ Cite error: The named reference su20040227 was invoked but never defined (see the help page).

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