Issue |
A&A
Volume 421, Number 2, July II 2004
|
|
---|---|---|
Page(s) | 659 - 666 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20035955 | |
Published online | 22 June 2004 |
A cool disk in the Galactic Center?
Max-Planck-Institut für Astrophysik, Karl- Schwarzschildstr. 1, 85740 Garching, Germany
Corresponding author: B. F. Liu, bifang@mpa-garching.mpg.de
Received:
30
December
2003
Accepted:
25
March
2004
We study the possibility of a cool disk existing in the Galactic
Center in the framework of the disk-corona evaporation/condensation model.
Assuming an inactive disk near the gravitational capture
distance left over from an earlier evolutionary stage,
a hot corona should form above the disk since there is a continuous
supply of hot gas from stellar winds of the close-by massive stars.
We study the interaction between the disk and the corona. Whether the
cool disk can survive depends on the mass exchange between disk and
corona which is determined by the energy and pressure balance.
If evaporation is the dominant process and the rate is larger than the
Bondi accretion rate in the Galactic Center, the disk will be depleted
within a certain time and no persistent disk will exist. On the other
hand, if the interaction results in hot gas steadily condensing into
the disk, an inactive cool disk with little gas accreting towards the
central black hole might survive in the Galactic Center. For this case
we further investigate the Bremsstrahlung radiation from the hot corona and
compare it with the observed X-ray luminosity. Our model
shows that, for standard viscosity in the corona (), the mass
evaporation rate is much higher than the Bondi accretion rate and the
coronal density is much larger than that inferred from Chandra observations. An
inactive disk can not survive such strong evaporation. For
small viscosity (
) we find condensation solutions.
But detailed coronal structure computations show that in this case
there is too much X-ray radiation from the corona to be in
agreement with the observations. From this modeling we conclude that
there should be no thin/inactive disk presently in the Galactic
Center. However we do not exclude that the alternative non-radiative
model of Nayakshin ([CITE]) might instead be realized in
nature and shortly discuss this question.
Key words: accretion, accretion disks / black hole physics / Galaxy: center
© ESO, 2004
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