Cygnus X-1
Galactic X-ray source in the constellation Cygnus that is very likely a black hole / From Wikipedia, the free encyclopedia
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Cygnus X-1 (abbreviated Cyg X-1)[11] is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole.[12][13] It was discovered in 1965 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).[14][15] 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[5][6] 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]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Cygnus |
Right ascension | 19h 58m 21.67574s[1] |
Declination | +35° 12′ 05.7845″[1] |
Apparent magnitude (V) | 8.95[2] |
Characteristics | |
Spectral type | O9.7Iab[2] |
U−B color index | −0.30[3] |
B−V color index | +0.81[3] |
Variable type | Ellipsoidal variable |
Astrometry | |
Radial velocity (Rv) | −2.70±3.2[2] km/s |
Proper motion (μ) | RA: −3.812±0.015 mas/yr[1] Dec.: −6.310±0.017 mas/yr[1] |
Parallax (π) | 0.4439 ± 0.0149 mas[1] |
Distance | 7,300 ± 200 ly (2,250 ± 80 pc) |
Absolute magnitude (MV) | −6.5±0.2[4] |
Details | |
Cygnus X-1 | |
Mass | 21.2[5][6] M☉ |
Details | |
HDE 226868 | |
Mass | 20–40 M☉ |
Radius | 20–22[7] R☉ |
Luminosity | 3–4×105[7] L☉ |
Surface gravity (log g) | 3.31±0.07[8] cgs |
Temperature | 31000[9] K |
Rotation | every 5.6 days |
Age | 5[10] Myr |
Other designations | |
Database references | |
SIMBAD | data |
Cygnus X-1 belongs to a high-mass X-ray binary system, located about 2.22 kiloparsecs from the Sun,[18] that includes a blue supergiant variable star designated HDE 226868,[19] 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.[20] Matter in the inner disk is heated to millions of degrees, generating the observed X-rays.[21][22] A pair of relativistic jets, arranged perpendicularly to the disk, are carrying part of the energy of the infalling material away into interstellar space.[23]
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.[10]
Cygnus X-1 was the subject of a friendly scientific wager between physicists Stephen Hawking and Kip Thorne in 1975, with Hawking hoping to lose.[24] Hawking bet that it was not a black hole. He 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[update], this hypothesis lacked direct empirical evidence but was generally accepted based on indirect evidence.[25]