Source X ultralumineuse

In Astrophysical, a ultralumineuse source X (of the English Ultraluminous X-ray source), shortened ULX indicates an extremely luminous astrophysical object in the field of the x-rays which is not the supermassif Black hole center of a Galaxie (in this case, one speaks about Quasar or AGN). The threshold of power radiated in the field of x-rays (typically in the band 0,1-6 keV) is of 10 32 Watt S, is more 250 000 times power emitted by the Sun in all the fields of Wavelength. The emitted power is measured knowing the received Density flux object and its distance, by supposing its isotropic emission . The designation of ultralumineux comes from what a priori only of the atypical objects can radiate such a quantity of energy. Indeed, the important emission of x-rays is in general interpreted as being due to the Accrétion of matter by a compact Objet, typically a neutron star or a Black hole. The maximum accretion rate, and consequently the luminosity released by the process (by supposing this one stationary, to see below) are however limited by the mass of the object. This limit is called Luminosité of Eddington, of the name of the Astronome English Arthur Eddington. A ultralumineuse source X in general requires to have to make with an extremely massive object.

Nature of sources X ultralumineuses

A ultralumineuse source X gives primarily place to three possible interpretations: either the accrétant object is sufficiently massive so that its high luminosity remains lower than the luminosity of Eddigton, or its luminosity is supérieuse with that of Eddington, or finally there is an error of interpetation in the luminosity of the object.

Massive black holes

The luminosity of Eddington has as a value, in solar unit of Luminosité,

L_ {\ rm Edd} = 3, \! 3 \ times 10^4 \ left (\ frac {M} {M_ \ odot} \ right) L_ \ odot

where

M/M_ \ odot

represents the mass of the object accrétant in unit of the mass of the Sun. A ultralumineuse source X thus requires a accretor object of a mass at least equal to eight solar masses. The theory of neutron stars indicates that such objects cannot exceed a mass of 2 or 3 solar masses (the exact figure is not known with precision, it depends on the structure of the equation of state of the matter which describes these objects). An object of 8 solar masses or more cannot thus be a neutron star, it is thus a Black hole. Such black holes are potential candidates to explain the ULX. It is necessary however that those are sufficiently massive. The black holes are divided into three classes, stellar Black hole (resulting from the gravitational collapse of a massive star), supermassif Black hole, much more massive, located at the center of the Galaxie S, and intermediate Black hole of a mass ranging between that of these two classes of objects. A massive stellar black hole (10 solar masses or more) or an intermediate black hole is a possible candidate with the statute of ULX.

Object super Eddington

It is possible that the luminosity of an object exceeds the luminosity of Eddington, one speaks in this case about object “super Eddington”, but in this case, the release of energy results in a modification of the structure of the object. Indeed, the luminosity of Eddington is calculated by supposing the object in hydrostatic balance. A Supernova is an extreme example of object whose luminosity exceeds (of much) the luminosity of Eddington. A Rémanent of supernova can also be to him extremely luminous. The Nebulous of the Crab, the remanent one of the most luminous supernova known radiates several hundreds of thousands of times more than the Sun (though not only in the field of x-rays). However, this state is only transitory, and as the remanent one extends, it becomes less and less luminous.

Mistakes in interpretation

Two types of errors can lead to a bad estimate of the luminosity of the object:

On the one hand, it is possible that the distance from the object is different from what is estimated, for example if it is about a Quasar located in background of a galaxy. Source X can be allotted to the object of before plan wrongly, whereas it is actually the heart of the quasar of background. This one is even more luminous, but its nature is more common, namely the supermassif black hole of the galaxy host of the quasar.
In addition, it is possible that the emission of the object is anisotropic. If the maximum of emission is directed towards the Ground with an emission concentrated into two jet S ends, the total luminosity deduced by supposing the isotropic emission can be overestimated considerably. In this case, the source than is actually considered much less luminous and in provanance of a more typical object.

Distribution of the ULX

The ULX are rare objects. None is listed in our Galaxie. Only one is listed in the Galaxie of the Triangle (M33), under the name of M33 X-8. It is besides the strongest source of x-rays of all the local Groupe. One seldom finds several ULX by galaxy.

M82 X-1, located in the galaxy M82 (sometimes called galaxy of the Cigar because of its form), discovered in 1994, is a very intense source of x-rays (up to 10 34 W) regarded as being an intermediate potential black hole of more than 1000 solar masses.

NGC 5204 X-1 is a source emitting approximately 3× 10 32 W, located in the galaxy NGC 5204. Its optical counterpart is known, it acts of a star of spectral Type B. a stellar black hole of high mass is regarded as the compact object most probable of this source.

See too

Luminosity of Eddington
Ultra-luminous Infrared Galaxy (ULIRG)

Random links: