Centaurus X-3 (4U 1118-60) is an

X-ray pulsar X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity. The X-ray periods range from as little as a fraction of a second to as much as several m ...

with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation

Centaurus Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. ...

. The system consists of a

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...

orbiting a massive, O-type

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spa ...

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

dubbed Krzeminski's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray emission.

History

Centaurus X-3 was first observed during experiments of cosmic X-ray sources made on May 18, 1967. These initial X-ray spectrum and location measurements were performed using a

sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are used to ...

. In 1971, further observations were performed with the Uhuru satellite, in the form of twenty-seven 100-second duration sightings. These sightings were found to pulsate with an average period of 4.84 seconds, with a variation in the period of 0.02 seconds. Later, it became clear that the period variations followed a 2.09 day

sinusoidal A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the '' sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often in m ...

curve around the 4.84 second period. These variations in arrival time of the pulses were attributed to the

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

caused by orbital motion of the source, and were therefore evidence for the binary nature of Centaurus X-3. Despite detailed data from the Uhuru satellite as to the orbital period of the binary, and the pulsation period in the X-ray band as well as the minimum mass of the occulting star, the optical component remained undiscovered for three years. This was partly because Cen X-3 lies in the plane of the Galaxy in the direction of the

Carina Spiral Arm Carina may refer to: Places Australia * Carina, Queensland, a suburb in Brisbane * Carina Heights, Queensland, a suburb in Brisbane * Carina, Victoria, a locality in Mildura Serbia * Carina, Osečina, a village in the Kolubara District Pe ...

, and so observations were forced to differentiate among dozens of faint objects. Centaurus X-3 was finally identified with a faint, heavily reddened variable star lying just outside the error box predicted by Uhuru observations. The visible star was later named after its discoverer, Poland astronomer Wojtek Krzemiński. Centaurus X-3 was the first sources observed by the Russian x-ray telescope

ART-XC The Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) is an X-ray telescope with a grazing incidence mirror that is capable of capturing high energy X-ray photons within the 5-30 keV energy range. This telescope is one of the two X-ray t ...

. An image was released with the title "First Light Image of the

Spektr-RG Spektr-RG ( Russian: Спектр-РГ, ''Spectrum'' + '' Röntgen'' + ''Gamma''; also called Spectrum-X-Gamma, SRG, SXG) is a Russian–German high-energy astrophysics space observatory which was launched on 13 July 2019. It follows on from th ...

Observatory", showing the source imaged by the individual telescopes of ART-XC, as well as the light curve of Centaurus X-3 folded at its pulse period of 4.8s.

System

Centaurus X-3 is located in the galactic plane about 5.7

kiloparsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

away, towards the direction of the

Carina–Sagittarius Arm The Carina–Sagittarius Arm (also known as the Sagittarius Arm or Sagittarius–Carina Arm, labeled -I) is generally thought to be a minor spiral arm of the Milky Way galaxy. Each spiral arm is a long, diffuse curving streamer of stars that ra ...

, and is a member of an occulting

spectroscopic binary A binary star is a system of two star, stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separa ...

system. The visible component is Krzeminski's Star, a

; the X-ray component is a rotating, magnetized

X-ray component

The X-ray emission is fueled by the accretion of matter from the distended atmosphere of the blue giant falling through the inner

Lagrangian point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of th ...

, L1. The overflowing gas probably forms an

accretion disc An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other f ...

and ultimately spirals inwards and falls onto the neutron star, releasing

gravitational potential energy Gravitational energy or gravitational potential energy is the potential energy a massive object has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field, which is released (conv ...

. The

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

of the neutron star channels the inflowing gas onto localized hot spots on the neutron star surface where the X-ray emission occurs. The neutron star is regularly eclipsed by its giant companion every 2.1 days; these regular X-ray eclipses last approximately 1/4 the orbital period. There are also sporadic X-ray off durations. The spin period history of Centaurus X-3 shows a spin-up trend that is very prominent in the long-term decrease in its pulse period. This spin-up was first noted in Centaurus X-3 and

Hercules X-1 Hercules X-1 (Her X-1), also known as 4U1656+35, is a moderately strong X-ray binary source first studied by the Uhuru satellite. It is composed of a neutron star accreting matter from a normal star (HZ Her) probably due to Roche lobe overflow. ...

and is now noted in other X-ray pulsars. The most feasible way of explaining the origin of this effect is by a torque exerted on the neutron star by accreting material.

Krzeminski's Star

Krzeminski's Star is a 20.5

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

(), slightly

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

hot massive star with a radius of and spectral type O6-7 II-III. There is little doubt as to the correctness of the optical candidate, since it is in apparent agreement with the period and phase of Cen X-3, and exhibits the same similarity in its double wave and amplitude light curve seen in other known massive binary systems. The double wave ellipsoidal light variations are produced by a tidally deformed giant that nearly fills its

Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, wit ...

. The visible component corresponds to an OB II class star, comparable with the mass derived from X-ray data, consistent with the minimum radius that has been fixed by X-ray eclipse duration.

References

External links