Microquasar

In Astronomy, a microquasar is a binary star containing a compact object such as a neutron star or a Black hole, and which produces jets a speed close to the Speed of light.

Presentation

The microquasars are binary stars having the same essential ingredients as the Quasar S: a Black hole, a Disc of accretion and jets. The term was invented by I. Felix Mirabel and Luis F. Rodríguez in a famous article describing the observation of relativistic jets supraluminic in a galactic system called GRS 1915+105. The microquasars are a subset of binary stars producing of x-rays, called the binary X.

Differences between quasars and microquasars

The microquasars and the quasars having the same essential ingredients, they share same physics. In other words, the physical phenomena present in the ones are also observed in the others. The principal difference between the two is the mass of the black hole. In the microquasars, there is a stellar Black hole of some solar masses, until ten solar masses. The black holes in the quasars are known as supermassifs and have a mass of several million even a few billion solar masses.

For a accrétant black hole of the matter of the Disc of accretion at the maximum rate of Eddington, the Température characteristic of a black Corps with the last stable circular orbit is given roughly by:

$T \ sim 2 \ times 10^7 M^ {- 1/4}$

where $M$ is the mass of the black hole. Thus, more the mass is small, more the temperature characteristic of the interior of the accretion disc is large. For this reason the Quasar S emit mainly in the optical field and Ultraviolet, while the discs of the microquasars emit mainly in the X-rays.

Relativistic jets and jets supraluminic

The characteristic which difference the microquasars of the others binary X is the presence of jets. These jets are mainly observed in the field of the waves radio (it was the case of GRS 1915+105 and GRO J1655-40 in particular). The jets observed in the microquasars are known as relativistic when they reach a speed close to the Speed of light. This designation comes owing to the fact that only the relativity of Albert Einstein makes it possible to describe them correctly.

According to the distance and jetting the angle of the jets in the sky, it happens that these relativistic jets have, seemingly , a speed higher than that of the light. In this case, one speaks about supraluminic jets .

The origin of the jets is still badly included/understood, although it is certain that they are launched very close to the central black hole, as for the quasars. One of the models suggested consists in saying that there exists a jet known as MHD car-collimated by the vertical Magnetic field, and who is produced by the accretion disc, and that under certain conditions, of the cascades of pairs electron S Positron S are formed. These pairs would be then collimées by jet MHD, and would be ejected at speeds ultra-relativists, by producing the famous jets observed out of radio.

Variability

The microquasars are characterized by a very strong variability in x-rays. It was observed in several microquasars an evolution in typical form of Hystérésis, and which remains to be explained. Also, of the oscillations quasi-periodicals ( QPO S ) at low and high frequencies are observed.

Examples of microquasars

The example the most famous remainder GRS 1915+105 which to date seems to be the microquasar with the greatest mass of black hole (ten solar masses) and the greatest accretion rate on the black hole. This object produces jets permanently. GRO J1655-40 was the second object in which jets supralumic were observed. The most clearly example of hysteresis was observed in GX 339-4, while S 433 is known to have permanent relativistic jets and in Précession, forming splendid a Nébuleuse.

See too

Binary X
active Core of galaxy
Quasar
QPO S

References

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