Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photon Ring and Observational Appearance of a Hairy Black Hole   Recently, the image of a Schwarzschild black hole with an accretion disk has
been revisited, and it showed that the "photon ring", defined as highly bent
light rays that intersect the disk plane more than twice, is extremely narrow
and makes a negligible contribution to the total brightness. In this paper, we
investigate the observational appearance of an optically and geometrically thin
accretion disk around a hairy black hole in an Einstein-Maxwell-scalar model.
Intriguingly, we find that in a certain parameter regime, due to an extra
maximum or an "ankle-like" structure in the effective potential for photons,
the photon ring can be remarkably wide, thus making a notable contribution to
the flux of the observed image. In particular, there appears a wide and bright
annulus, which comprises multiple concentric bright thin rings with different
luminosity, in the high resolution image.

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The categories of this paper are: math
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The categories of this paper are: q-bio
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The categories of this paper are: astro-ph
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The categories of this paper are: eess
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: econ
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
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The categories of this paper are: adap-org