A microquasar, a smaller version of a

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

, 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. They are the remnants of supernova explosions, which may be ...

with a mass several times that of its companion star, observable in sufficient details, in our own or nearby galaxy. The matter being pulled from the companion

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

forms an accretion disk around the

black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

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

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s. The disk also projects narrow streams or " jets" of subatomic particles at near- light speed, generating a strong

radio wave Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...

emission.

Overview

In 1979, SS 433, in our own galaxy, became the first microquasar to be discovered, when Margon et al. observed its relativistic jets. It was thought to be the most exotic case until similar objects such as GRS 1915+105 were confirmed in 1994. In some cases, blobs or "knots" of brighter plasma within the jets appear to be traveling faster than the speed of light, an optical illusion called superluminal motion which is caused by sub-light-speed particles being projected at a small angle relative to the observer. The 1996 Bruno Rossi Prize of the American Astronomical Society was awarded to Felix Mirabel and Luis Rodríguez for their discovery of the superluminal motion 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. 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 (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

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 changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

(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 or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

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

{{Portal bar, Astronomy, Stars, Outer space * Astronomical radio sources

Overview

See also

References