Evolution of X-ray emission from young massive stellar clusters
L. M. Oskinova
The evolution of young massive stellar cluster is modeled in order to
explain the striking difference observed in the levels of X-ray emission
between clusters of different age. It is shown that the level and
character of soft (0.2-10 keV) X-ray emission change drastically with
cluster age and are tightly linked with stellar evolution. Assuming
instantaneous burst of star formation and standard initial mass
function, the total X-ray luminosity of all low-mass stars 0.1-
3 Msun is higher than the total luminosity of the cluster's
high-mass stars (8 - 100 Msun). The same time, massive stars
are the brightest X-ray point sources, although they become much dimmer
when they evolve to Wolf-Rayet (WR) star phase. A supernova remnant
emission may be a dominant X-ray source in an old enough cluster, but
only for a relatively short time of a few thousand years. The diffuse
X-ray emission originates from the intercluster wind heated by the
kinetic energy of stellar winds and supernova explosions. When massive
stars reach the WR phase, the level of diffuse emission rises due to the
powerful WR stellar winds. Subsequent SN explosions pump the level of
diffuse emission even higher. The clusters older then \approx 2 Myr
may have no bright stellar point sources, but a relatively high level of
diffuse emission. The above scenario provides a plausible explanation of
the X-ray observations of the Arches and the Quintuplet cluster in the
Galaxy as well as of a sample of LMC clusters.
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