Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational collapse of spherically symmetric perfect fluid with
  kinematic self-similarity   Analytic spherically symmetric solutions of the Einstein field equations
coupled with a perfect fluid and with self-similarities of the zeroth, first
and second kinds, found recently by Benoit and Coley [Class. Quantum Grav. {\bf
15}, 2397 (1998)], are studied, and found that some of them represent
gravitational collapse. When the solutions have self-similarity of the first
(homothetic) kind, some of the solutions may represent critical collapse but in
the sense that now the "critical" solution separates the collapse that forms
black holes from the collapse that forms naked singularities. The formation of
such black holes always starts with a mass gap, although the "critical"
solution has homothetic self-similarity. The solutions with self-similarity of
the zeroth and second kinds seem irrelevant to critical collapse. Yet, it is
also found that the de Sitter solution is a particular case of the solutions
with self-similarity of the zeroth kind, and that the Schwarzschild solution is
a particular case of the solutions with self-similarity of the second kind with
the index $\alpha = 3/2$.

27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an