Microquasar

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Artist's impression of a microquasar.

Microquasars are astronomical objects that can be viewed as miniature versions of quasars due to the properties observed .

Characteristics

If the compact component is definitely a black hole , the term microquasar or Black Hole X-ray Binary (BHXB) is usually used in the terminology. Sometimes one still speaks of microquasars, even if the compact component could be a neutron star . This is explained by the fact that it is often not clear which object the compact component is. For some time now, SS 433 has been called a microquasar, although it has only recently been certain that a stellar black hole is located here. The differentiation between a neutron star or a hole succeeds when astronomers can derive the mass of the compact component (e.g. from Kepler's laws). If it is above about three solar masses , it is almost certainly a stellar black hole. Other objects simply do not fit into the observations and model ideas.

If it is an accreting pulsar , i.e. a neutron star as a compact object, the designation AXP has become established for these X-ray binary star systems . This stands for Accreting X-ray Pulsar (dt. Accreting X-ray pulsar).

Like a quasar , which is an active galaxy core with a supermassive black hole , the microquasar shows strong and variable radio emissions , which can often be observed as radio jets , as well as an accretion disk that is very luminous in the optical and X-ray range . The accretion disk is formed by a transfer of matter onto the compact object.

Development theories

The most widely used theory assumes that one of the two stars of a binary pair to suck at the end of its life cycle, following the collapse to a neutron star or a black hole starts by its extreme gravitational field matter from its companion star and thus to form an accretion disk. Under certain circumstances, the flow of matter is so great that the compact component ejects the matter in the form of collimated jets of matter, the so-called cosmic jets , at almost the speed of light.

Furthermore, one could suspect that a microquasar can arise from a black hole migrating into a star system.

Observations and occurrences

The X-ray satellite GRANAT discovered GRS 1915 + 105 (= V1487 Aquilae) at a distance of 40,000 light years in 1994 . The microquasar consists of a star with about one solar mass orbiting a black hole with ~ 14 times the solar mass, and is thus one of the largest known stellar black holes to date.

V5641 Sagittarii (= LS 5036) is another and, at a distance of 9,100 light years, much closer microquasar. The two radio jets are about 2.6 billion km long. That corresponds to about 2.6 hours of light and would be projected onto our solar system, starting from the sun, and extending roughly between Saturn and Uranus.

When observing V5641 Sgr, however, it was found that it radiates rather weakly in the X-ray range. This could indicate that future searches could classify many such X-ray weak objects as quasars. If so, it could be that a substantial, if not a major, part of the high-energy particles and radiation in the Milky Way can be traced back to microquasars.

The closest known microquasar and its black hole is V4641 Sagittarii , only about 1,500 light years from Earth.

Examples in the Milky Way

Other well-known microquasars in the Milky Way are: Cyg X-1 , Cyg X-3 , Cir X-1 , XTE J1748-288 , LS 5039 , GRO J1655-40 , GRS 1915 + 105 , SS 433 , XTE J1550-564 and Sco X-1 .

Ultra-luminous X-ray sources in other galaxies

Due to the anisotropic alignment of the jets and the relativistic effects, the radiation is bundled in the direction of the jets. It is therefore believed that the ultra-bright X-ray sources in other galaxies are microquasars, whose jets are precisely aligned with Earth. The term ultra- luminous X-ray sources comes from the fact that the luminosity exceeds the Eddington limit of black holes with stellar masses.

Microquasars as gamma-ray binary stars

Gamma ray double stars emit electromagnetic radiation with energies above 200 keV . The gamma radiation in the case of the microquasars is the result of an inverse Compton scattering of ultraviolet radiation with charged particles on the relativistic jet of the microquasar. There is a time correlation between the radio radiation and the gamma radiation. The gamma radiation always occurs with a time delay of a few days and the inverse Compton scattering should therefore appear in the outer areas of the jet. The energy of the gamma radiation can have values ​​of 10 36 erg (10 29 J ) and is thus in the order of magnitude of the emitted X-rays.

Importance to astronomy

The relativistic radio jets are of particular interest in microquasars . The jets form near the black hole, so the timescales of changes are proportional to the mass of the black hole. A common quasar has up to several million solar masses and microquasars sometimes only a few solar masses.

Due to the different mass scales between quasars and microquasars the temporal variability can such jets based on microquasars as if in fast motion are studied. Changes in the jets of a microquasar within a day often correspond to changes in the jets of a quasar over centuries. This radiation of observed particles and formation of the jets, which is relatively fast compared to quasars, makes it possible to scientifically observe microquasars and their changes in much shorter periods.

See also

Web links

Individual evidence

  1. ↑ a b Lexicon of Astrophysics. In: Andreas Müller. Spectrum.de, accessed on July 1, 2019 .
  2. ↑ Stefan Deiters: Microquasars: Surprisingly powerful jets. In: astronews.com. July 7, 2010, accessed August 18, 2011 .
  3. ↑ Researchers discover microquasars in our galaxy. Huge compact source of high-energy gamma radiation. In: Press release RUB. RUB press office , July 8, 2005, accessed on August 18, 2011 .
  4. ↑ Thomas Weyrauch: Black holes migrate through the Milky Way. In: Spaceman Net. May 3, 2009, accessed on August 18, 2011 (source only confirms the existence of stray black holes).
  5. ↑ GRS 1915 + 105: Erratic Black Hole Regulates Itself. In: harvard.edu. Chandra X-ray Center, 2009, accessed August 18, 2011 .
  6. ↑ a b Andreas Müller: Astro-Lexicon M 4. Microquasar. In: Wissenschaft-online.de. August 2007, accessed August 18, 2011 .
  7. ^ I. Félix Mirabel: The Early History of Microquasar Research . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1206.1041 .
  8. ^ G. Piano, M. Tavani, V. Vittorini, et al .: The AGILE monitoring of Cygnus X-3: transient gamma-ray emission and spectral constraints . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1207.6288v1 .