Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Saha Ionization Formula and the Voids   The ultra-low density limit of Saha ionization formula suggests that, in this
limit, matter would prefer to remain ionized.This has a very important
implication for cosmic structures known as Voids.These are ultra-low density
(much less than average density of matter in the Universe) regions in the
galactic clusters and superclusters.The ionization formula implies that matter
trapped in the Voids should be ionized.Therefore, we expect a very faint
radiation glow from the Voids resulting from the motion of the charged
particles.

29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
1
The categories of this paper are: cs