Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic background radiation in the vicinity of a Schwarzschild black
  hole: no classic firewall   The Cosmic Blackbody Background Radiation pervades the entire Universe, and
so falls into every astrophysical black hole. The blueshift of the infalling
photons, measured by a static observer, is infinite at the event horizon. This
raises a question as to whether a "firewall" of high energy density may form
just outside the horizon, or whether the effect can be attributed exclusively
to a singular behavior of the static observer's frame at the horizon. In
principle, the presence of such firewall may alter the motion of the infalling
matter, influence the black hole evolution, or even invalidate the {\it vacuum}
Einstein field equation solution as a realistic approximation for black holes.
In this paper we show by means of analytic calculations that all these effects
indeed exist, but their magnitude is typically negligibly small, even though
the matter stress tensor is divergent in the static frame at $r=2M$. That is
not surprising because of the divergent relation of that frame to a freely
falling frame as $r \rightarrow 2M$; however it represents a kind of classical
analogue for the Black Hole Complementarity principle that has been proposed
for quantum effects near a black hole. What is perhaps more surprising is the
divergence of the radiation stress tensor for massive particles moving on
circular geodesic orbits for values of $r$ approaching $r = 3M$. However such
orbits will not occur for infalling matter in realistic accretion discs.

1
The categories of this paper are: cs
3
The categories of this paper are: physics
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph