A microquasar, the smaller version of a

quasar A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...

, is a compact region surrounding a

stellar black hole A stellar black hole (or stellar-mass black hole) is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. The process is observed as a hypernova explosion or as a gam ...

with a mass several times that of its

companion star A binary star is a system of two stars that are 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 separate stars, in wh ...

. The matter being pulled from the companion

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 ...

forms an accretion disk around the

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

. This accretion disk may become so hot, due to friction, that it begins to emit

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 ...

s. The disk also projects narrow streams or " jets" of subatomic particles at near-

light speed The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special relativity, special theory of relativity, is ...

, generating a strong

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...

emission.

Overview

In 1979, SS 433 became the first microquasar to be discovered. It was thought to be the most exotic case until similar objects such as

GRS 1915+105 GRS 1915+105 or V1487 Aquilae is an X-ray binary star system which features a regular star and a black hole. It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat. "GRS" stands for "GRANAT source", "1915" is the ...

were discovered in 1994. In some cases, blobs or "knots" of brighter

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

within the jets appear to be traveling faster than the speed of light, an

optical illusion Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide v ...

called

superluminal motion In astronomy, superluminal motion is the apparently faster-than-light motion seen in some radio galaxies, BL Lac objects, quasars, blazars and recently also in some galactic sources called microquasars. Bursts of energy moving out along the rel ...

which is caused by sub-light-speed particles being projected at a small angle relative to the observer. The 1996

Bruno Rossi Prize The Bruno Rossi Prize is awarded annually by the High Energy Astrophysics division of the American Astronomical Society "for a significant contribution to High Energy Astrophysics, with particular emphasis on recent, original work". Named after as ...

of the American Astronomical Society was awarded to Felix Mirabel and Luis Rodríguez for their discovery of the

of radio knots in GRS 1915+105, as well as the discovery of double-sided radio jets from galactic sources 1E1740.7-2942 and

GRS 1758-258 GRS may refer to: Education * Geneva Reformed Seminary, in Greenville, South Carolina * Gifted Rating Scales, an educational assessment test * Great River Charter Montessori School, in St. Paul, Minnesota Science * Gamma-ray spectrometer * Gamm ...

. Due to the smaller size of microquasars, many of the effects are scaled differently in relation to normal quasars. In quasars, the mean temperature of the accretion disk is several thousand degrees, while in a microquasar the mean temperature is several million degrees. The average size of the accretion disk of a quasar is , whereas in microquasars the average size is only . Quasars can project jets up to several million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s, whereas microquasars can project them only a few light-years; however, the "knots" within the jets of microquasars can exhibit a

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

(angular motion across the sky) on the order of a thousand times faster than that of knots within a quasar jet because observed microquasars (being within 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 ...

galaxy) are at typical distances on the order of kilo

parsec 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, and ...

s, rather than hundreds of megaparsecs to several gigaparsecs.

References

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Overview

See also

References