Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Upper bound on the radii of regular ultra-compact star photonspheres   We investigate the photonsphere in the background of regular asymptotically
flat compact stars. The analysis includes the general hairy compact star
considering the matter fields' backreaction on the metric in various gravity
theories. We prove that the photonsphere of the compact star has an upper bound
expressed in terms of the ADM mass of the spacetime. In the case of negative
isotropic trace, a stronger upper bound can be obtained.

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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
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The categories of this paper are: eess
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
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The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat