Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An Eccentric Disk Model for the Nucleus of M31   The nucleus of M31 may be a thick eccentric disk, composed of stars traveling
on nearly Keplerian orbits around a black hole or other dark compact object.
This hypothesis reproduces most of the features seen in HST photometry of the
center of M31; in particular the bright off-center source P1 is the apoapsis of
the disk. An eccentric disk can also explain the rotation curve and asymmetric
dispersion profile revealed by ground-based observations. The central object
must be smaller than 1 pc so that the potential felt by the disk is nearly
Keplerian. The disk eccentricity may be excited by a secular instability driven
by dynamical friction from the bulge.

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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
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The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: nucl-th
1
The categories of this paper are: cs
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The categories of this paper are: math-ph