{{Short description|Miniature analogue of a quasar caused by black hole accretion}} [[Image:Ss433 art big.gif|thumb|Artist's impression of the microquasar SS 433]] A '''microquasar''', a smaller version of a quasar, is a compact region surrounding a stellar black hole with a mass several times that of its companion star, observable in sufficient detail, in our own or nearby galaxy.<ref name="a">{{cite web|title=First Microquasar Found Beyond Our Milky Way|url=http://www.nrao.edu/pr/2012/microquasar/|website=www.nrao.edu|accessdate=19 January 2017}}</ref> The matter being pulled from the companion star forms an accretion disk around the black hole. This accretion disk may become so hot, due to friction, that it begins to emit X-rays.<ref name="b"/> The disk also projects narrow streams or "jets" of subatomic particles at near-light speed, generating a strong radio wave 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.<ref name="Margon">{{cite web |last1=Margon |first1=Bruce |title=Relativistic Jets in SS 433 |url=https://www.science.org/doi/abs/10.1126/science.215.4530.247 |website=science.org |publisher=Science, Vol 215, Issue 4530, pp. 247-252 |access-date=15 October 2024 |date=15 January 1982}}</ref> It was thought to be the most exotic case until similar objects such as GRS 1915+105 were confirmed in 1994.<ref name="b">{{cite web|title=Microquasars in the Milky Way|url=https://www.nrao.edu/pr/2000/vla20/background/superlum/|website=www.nrao.edu|accessdate=19 January 2017}}</ref>
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 direction to the observer.<ref name="b"/>
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.<ref name="prizelist">{{cite web|title=HEAD AAS Rossi Prize Winners|url=https://head.aas.org/rossi/rossi.recip.html#L|website=www.head.aas.org|accessdate=27 August 2017}}</ref><ref name="superluminal">{{cite journal |last1=Mirabel|first1=Felix|last2=Rodriguez|first2=Luis F.|date=1994|title=A superluminal source in the Galaxy|journal=Nature|volume=371|issue=6492|pages=46–48|doi=10.1038/371046a0|bibcode = 1994Natur.371...46M |s2cid=4347263}}</ref><ref name="gammasources">{{cite journal |last1=Mirabel|first1=Felix|date=1994|title=Multiwavelength approach to gamma-ray sources in the Galactic center region|journal=Astrophys. J. Suppl. Ser.|volume=92|pages=369–373|doi=10.1086/191980|bibcode = 1994ApJS...92..369M }}</ref>
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 {{convert|1|e9km2|e6mi2|abbr=off}}, whereas in microquasars the average size is only {{convert|1000|km2|abbr=on|comma=gaps}}. Quasars can project jets up to several million light-years, whereas microquasars can project them only a few light-years; however, the "knots" within the jets of microquasars can exhibit a proper motion (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 galaxy) are at typical distances on the order of kiloparsecs, rather than hundreds of megaparsecs to several gigaparsecs.<ref>{{cite web|title=Microquasars as sources of high energy phenomena -I.F. Mirabel|url=https://ned.ipac.caltech.edu/level5/Sept02/Mirabel/Mirabel1.html|website=ned.ipac.caltech.edu|accessdate=19 January 2017}}</ref>
== See also == * List of microquasars
== References == {{reflist}}
{{Black holes}} {{Portal bar|Astronomy|Stars|Outer space}}
Category:Microquasars * Category:Astronomical radio sources