Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Effect of Sources on the Inner Horizon of Black Holes   Single pulse of null dust and colliding null dusts both transform a regular
horizon into a space-like singularity in the space of colliding waves. The
local isometry between such space-times and black holes extrapolates these
results to the realm of black holes. However, inclusion of particular scalar
fields instead of null dusts creates null singularities rather than space-like
ones on the inner horizons of black holes.

20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex