Cygnus X-3 is a high-mass X-ray binary ( HMXB), one of the stronger binary X-ray sources in the sky. It is often considered to be a microquasar, and it is believed to be a

compact object In astronomy, the term compact star (or compact object) refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects ha ...

in a binary system which is pulling in a stream of gas from an ordinary

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 ...

companion. It is one of only two known HMXBs containing a Wolf-Rayet star. It is invisible visually, but can be observed at

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a tr ...

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

, and gamma-ray wavelengths.

Observations

Cygnus X-3 is a prominent X-ray source, with soft and hard X-rays both varying in intensity. Periods where the hard X-rays are at minimum intensity are known as soft states. It is less than half a degree from a gamma-ray pulsar, but is itself a weak gamma-ray source. It also shows periodic gamma-ray flares, apparently all occurring during the soft state. It is undetectable at visual wavelengths due to extreme

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the Endling, last individual of the species, although the Functional ext ...

in the galactic plane. However, there is an

point source at its position. Cygnus X-3 is also notable as the only microquasar firmly detected in the high energy gamma rays in the range >100 MeV. Because of the variations in emission at various wavelengths, Cygnus X-3 has been given the

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the const ...

V1521 Cygni.

Flares

Cygnus X-3 is notable for its intense X-ray emission, but it is also remarkable for its gamma-ray and radio flares during which it becomes the brightest radio source in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

. The gamma-ray flares apparently occur in the quiet radio period before a major radio flare. During the giant radio flares, a relativistic jet has been resolved within about of being aimed directly towards us.

Binary system

Cygnus X-3 shows consistent variations across all wavelengths with a period. The nature of the infrared spectrum and the x-ray emission is interpreted as a binary system containing a Wolf-Rayet (WR) star and a compact object. The variations have been interpreted as eclipses, but this is thought to be unlikely because there are not well-defined periodic dips in the brightness. The orbit of the binary system is not known accurately, other than the period. Therefore, the masses of the components are not known accurately. Orbital analysis suggested that the mass of the compact object is less than , probably around . It could possibly be 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. w ...

but is more likely to be a black hole. The combination of a WR star and a black hole would be the only known example. While the combination of WR star and compact object would be unique, the WR component will itself almost certainly become a black hole very quickly by astronomical timescales. A

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

or possible direct collapse to a black hole is expected within a million years or so. However, modelling of the Cygnus X-3 system suggests it is most likely that the binary will be disrupted by any supernova event. The

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

events from Cygnus X-3 had previously led to exotic proposals such as a star made of

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly ...

s, but are now explained as being produced in the relativistic jet. The explanation for the unusual relationship between the x-rays and the gamma-ray and radio flares is that the compact objects produces jets along its axis of rotation, within the dense wind from the WR star. These jets evacuate a cocoon within the wind when entering the hard state, and are then quenched by the wind when entering the soft state. Flares are produced during the transition to the hard state as the jets are interacting with the dense wind.

Distance

Cygnus X-3 lies in the direction of the

Cygnus OB2 Cygnus OB2 is an OB association that is home to some of the most massive and most luminous stars known, including suspected Luminous blue variable Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni. The region is emb ...

association in the Cygnus X complex, although it is much further away. Its distance can be estimated relative to Cygnus OB2 by studying the X-ray halo produced by dust between us and Cygnus X-3. The distance to Cygnus OB2 is not known precisely, but this method gives possible distances to Cygnus X-3 of or . There is a small X-ray source from Cygnus X-3 that varies with the same period by a phase lag of about . This is thought to be a Bok globule at approximately the same distance as Cygnus X-3. Using molecular line emission from this object, two possible distances are found to be and . A statistical mean is .

References

External links