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Cygnus X-1
Cygnus X-1 (abbreviated Cyg X-1) is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole. 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). 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 and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole. 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.
Cygnus X-1 is a high-mass X-ray binary system located about 7,000 light-years away, that includes a blue supergiant variable star. 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. Matter in the inner disk is heated to millions of degrees, generating the observed X-rays. A pair of relativistic jets, arranged perpendicularly to the disk, are carrying part of the energy of the infalling material away into interstellar space.
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.
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. Hawking conceded the bet in 1990 after observational data had strengthened the case that there was indeed a black hole in the system.
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. 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 1–15 Å 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.
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.
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, which led to the discovery of 300 new X-ray sources. Extended Uhuru observations of Cygnus X-1 showed fluctuations in the X-ray intensity that occurs several times a second. This rapid variation meant that the X-ray generation must occur over a compact region no larger than ~105 km (roughly the size of Jupiter), 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, 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. On the celestial sphere, this star lies about half a degree from the 4th-magnitude star Eta Cygni. 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.
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Cygnus X-1
Cygnus X-1 (abbreviated Cyg X-1) is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole. 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). 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 and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole. 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.
Cygnus X-1 is a high-mass X-ray binary system located about 7,000 light-years away, that includes a blue supergiant variable star. 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. Matter in the inner disk is heated to millions of degrees, generating the observed X-rays. A pair of relativistic jets, arranged perpendicularly to the disk, are carrying part of the energy of the infalling material away into interstellar space.
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.
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. Hawking conceded the bet in 1990 after observational data had strengthened the case that there was indeed a black hole in the system.
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. 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 1–15 Å 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.
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.
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, which led to the discovery of 300 new X-ray sources. Extended Uhuru observations of Cygnus X-1 showed fluctuations in the X-ray intensity that occurs several times a second. This rapid variation meant that the X-ray generation must occur over a compact region no larger than ~105 km (roughly the size of Jupiter), 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, 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. On the celestial sphere, this star lies about half a degree from the 4th-magnitude star Eta Cygni. 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.