Ultraluminous X-ray sources (ULXs) are located in external galaxies, their
X-ray luminosities (1039 - 1041 erg/s) are thousand
times greater than those
of brightest black holes in the Galaxy. ULXs may be supercritical accretion
disks around black holes of stellar masses (~10 Solar masses) like that in
SS433, or they may be a hypothetical intermediate-mass black holes (hundreds
- thousands Solar masses) with standard accretion disks.
We have carried out observations of stellar clusters related to the ULXs, in
South sky there were observations with the VLT (VIMOS, MOS) of clusters in
the Antennae galaxies (Fig. 1 and 2) and in NGC3256, in Northern sky with
the BTA (Scorpio) of clusters in NGC4485/4490 galaxies. We have discovered
that all the ULXs are located nearby to (inside about 200 pc) very young
star clusters (Fig. 3), all the clusters are younger than 5 Myrs. A
probability of occasional associations of the ULXs with the clusters is very
little (0.0000001), it is even less for young clusters.
We conclude:
1) The ULX progenitors are close binary systems with their star masses not
less than 50-100 Solar masses. They are black holes of "stellar masses" with
a supercritical accretion.
2) The ULX progenitors were ejected from the star clusters. The ejections
because of the Supernova explosion can not explain these data, there is not
a time both for stellar evolution and for the transportation from the
cluster to outside. The ejection occurs due to 3- and 4-body encounters in
the cluster centers at the very beginning stages of cluster evolution.
3) This confirmes the new ideas of stellar clusters formation. This
mechanism explains the well-known problem in our Galaxy - the problem of
massive run-away stars.
Published:
J.Poutanen, S.Fabrika, A.Valeev, O.Sholukhova, J.Greiner,
arXiv1210.1210
Contact - Fabrika S.N.
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Fig.1.
The interacting Antennae galaxies, the image taken with the Hubble Space
Telescope. Two bright white concentrations are nuclei of the merging
galaxies. Green circles with numbers indicate locations of the brightest
X-ray sources. Green rectangles show frames of the VIMOS spectrograph of the
VLT/Melipal telescope. The same frames are shown in the cornes, locations of
the ULXs are marked there with black circles
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