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キーワード:
Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO, Astrophysics, Galaxy Astrophysics, astro-ph.GA
要旨:
Since 1996 we have known that the Galactic Center (GC) displays a core-like
distribution of red giant branch (RGB) stars starting at ~ 10", which poses a
theoretical problem, because the GC should have formed a segregated cusp of old
stars. This issue has been addressed invoking stellar collisions, massive black
hole binaries, and infalling star clusters, which can explain it to some
extent. Another observational fact, key to the work presented here, is the
presence of a stellar disk at the GC. We postulate that the reason for the
missing stars in the RGB is closely intertwined with the disk formation, which
initially was gaseous and went through a fragmentation phase to form the stars.
Using simple analytical estimates, we prove that during fragmentation the disk
developed regions with densities much higher than a homogeneous gaseous disk,
i.e. "clumps", which were optically thick, and hence contracted slowly. Stars
in the GC interacted with them and in the case of RGB stars, the clumps were
dense enough to totally remove their outer envelopes after a relatively low
number of impacts. Giant stars in the horizontal branch (HB), however, have
much denser envelopes. Hence, the fragmentation phase of the disk must have had
a lower impact in their distribution, because it was more difficult to remove
their envelopes. We predict that future deeper observations of the GC should
reveal less depletion of HB stars and that the released dense cores of RGB
stars will still be populating the GC.
