Cygnus X-1

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) 8.72 - 8.93[3]
Characteristics
Spectral type O9.7Iab[4]
U−B color index −0.30[5]
B−V color index +0.81[5]
Variable type Ellipsoidal variable[3]
Astrometry
Radial velocity (Rv)−2.70±3.2[4] 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[6]
Details[7]
Black hole
Mass13.8 to 17.5+2.0
−1.0 M☉
Supergiant
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[8] Myr
Other designations
V1357 Cygni, BD+34°3815, HD 226868, HDE 226868, HIP 98298, SAO 69181[4]
Database references
SIMBADdata

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 2.3×10−23 W/(m2⋅Hz) (2.3×103 jansky).[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 300 km "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 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.[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]

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