Scorpius X-1
Encyclopedia
Scorpius
X-1 is an X-ray
source located roughly 9000 light years away in the constellation Scorpius. Scorpius X-1 was the first extrasolar X-ray source discovered, and, aside from the Sun
, it is the strongest source of X-rays in the sky
. The X-ray flux
varies day-to-day, and is associated with an optically visible star
, V818 Scorpii, that has an apparent magnitude
which fluctuates between 12-13.
at American Science and Engineering
in Cambridge, Massachusetts
, who launched an X-ray detector on an Aerobee 150 sounding rocket to look for X-ray emissions from Earth's moon. Instead, Scorpius X-1 became the first X-ray source discovered outside the Solar System
. The angular resolution
of the detector did not initially allow the position of Scorpius X-1 to be accurately determined. This led to suggestions that the source might be located near the Galactic center
, but it was eventually realized that it lies in the constellation Scorpius. As the first discovered X-ray source in Scorpius, it received the designation Scorpius X-1.
The Aerobee 150 rocket launched on June 12, 1962, detected the first X-rays from another celestial source (Scorpius X-1) at J1950 RA
Dec
. Sco X-1 is a LMXB in which the visual counterpart is V818 Scorpii.
Although the above reference indicates the rocket launch was on June 12, 1962, other sources indicate the actual launch was at 06:59:00 UTC on June 19, 1962.
Historical footnote:
"The instrumentation had been designed for an attempt to observe X-rays from the moon and was not equipped with collimation to restrict the field of view narrowly. As a result, the signal was very broad, and accurate definition of the size and position of the source was not possible. A similar experiment was repeated in October 1962 when the galactic center was below the horizon and the strong source was not present. A third attempt, in June 1963, verified the results of the June 1962 flight." The Galactic Center
is < 20° RA
and < 20° Dec
from Sco X-1, the two X-ray sources are separated by ~20° of arc and may not have been resolvable in the June 1962 flight.
Scorpius XR-1 has been observed at J1950 RA
Dec
.
In 1967 (before the discovery of pulsar
s), Iosif Shklovsky
examined X-ray and optical observations of Scorpius X-1 and correctly concluded that the radiation comes from a neutron star
accreting matter from a companion.
, about 60,000 times the total luminosity of the Sun. Scorpius X-1 shows regular variations of up to 1 magnitude
in its intensity, with a period of around 18.9 hours. The source varies irregularly in optical wavelength
s as well, but these changes are not correlated with the X-ray variations. Scorpius X-1 itself is a neutron star
whose intense gravity draws material off this companion into an accretion disk, where it ultimately falls onto the surface, releasing a tremendous amount of energy. As this stellar material accelerates in Scorpius X-1's gravitational field, X-rays are emitted. The measured luminosity for Scorpius X-1 is consistent with a neutron star which is accreting matter at its Eddington limit.
This system is classified as a low-mass X-ray binary; the neutron star is roughly 1.4 solar masses, while the donor star is only 0.42 solar masses. The two stars were probably not born together; recent research suggests that the binary may have been formed by a close encounter inside a globular cluster
.
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...
X-1 is an X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
source located roughly 9000 light years away in the constellation Scorpius. Scorpius X-1 was the first extrasolar X-ray source discovered, and, aside from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, it is the strongest source of X-rays in the sky
Sky
The sky is the part of the atmosphere or outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a pale blue surface because the air scatters the sunlight. The sky is sometimes...
. The X-ray flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
varies day-to-day, and is associated with an optically visible star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
, V818 Scorpii, that has an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
which fluctuates between 12-13.
Discovery and early study
Scorpius X-1 was discovered in 1962 by a team under Riccardo GiacconiRiccardo Giacconi
Riccardo Giacconi is an Italian/American Nobel Prize-winning astrophysicist who laid the foundations of X-ray astronomy. He is currently a professor at the Johns Hopkins University.- Biography :...
at American Science and Engineering
American Science and Engineering
American Science and Engineering Inc, is a US manufacturer of X-ray equipment and related technologies, originating in 1958 as a developer for NASA, with an early focus on X-ray astronomy led by Riccardo Giacconi...
in Cambridge, Massachusetts
Cambridge, Massachusetts
Cambridge is a city in Middlesex County, Massachusetts, United States, in the Greater Boston area. It was named in honor of the University of Cambridge in England, an important center of the Puritan theology embraced by the town's founders. Cambridge is home to two of the world's most prominent...
, who launched an X-ray detector on an Aerobee 150 sounding rocket to look for X-ray emissions from Earth's moon. Instead, Scorpius X-1 became the first X-ray source discovered outside the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. The angular resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
of the detector did not initially allow the position of Scorpius X-1 to be accurately determined. This led to suggestions that the source might be located near the Galactic center
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
, but it was eventually realized that it lies in the constellation Scorpius. As the first discovered X-ray source in Scorpius, it received the designation Scorpius X-1.
The Aerobee 150 rocket launched on June 12, 1962, detected the first X-rays from another celestial source (Scorpius X-1) at J1950 RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
. Sco X-1 is a LMXB in which the visual counterpart is V818 Scorpii.
Although the above reference indicates the rocket launch was on June 12, 1962, other sources indicate the actual launch was at 06:59:00 UTC on June 19, 1962.
Historical footnote:
"The instrumentation had been designed for an attempt to observe X-rays from the moon and was not equipped with collimation to restrict the field of view narrowly. As a result, the signal was very broad, and accurate definition of the size and position of the source was not possible. A similar experiment was repeated in October 1962 when the galactic center was below the horizon and the strong source was not present. A third attempt, in June 1963, verified the results of the June 1962 flight." The Galactic Center
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
is < 20° RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and < 20° Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
from Sco X-1, the two X-ray sources are separated by ~20° of arc and may not have been resolvable in the June 1962 flight.
Scorpius XR-1 has been observed at J1950 RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
.
In 1967 (before the discovery of pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
s), Iosif Shklovsky
Iosif Shklovsky
Iosif Samuilovich Shklovsky was a Soviet astronomer and astrophysicist...
examined X-ray and optical observations of Scorpius X-1 and correctly concluded that the radiation comes from a neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
accreting matter from a companion.
Characteristics
Its X-ray output is 2.3×1031 WWatt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
, about 60,000 times the total luminosity of the Sun. Scorpius X-1 shows regular variations of up to 1 magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
in its intensity, with a period of around 18.9 hours. The source varies irregularly in optical wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s as well, but these changes are not correlated with the X-ray variations. Scorpius X-1 itself is a neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
whose intense gravity draws material off this companion into an accretion disk, where it ultimately falls onto the surface, releasing a tremendous amount of energy. As this stellar material accelerates in Scorpius X-1's gravitational field, X-rays are emitted. The measured luminosity for Scorpius X-1 is consistent with a neutron star which is accreting matter at its Eddington limit.
This system is classified as a low-mass X-ray binary; the neutron star is roughly 1.4 solar masses, while the donor star is only 0.42 solar masses. The two stars were probably not born together; recent research suggests that the binary may have been formed by a close encounter inside a globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
.