Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Aschenbach effect: unexpected topology changes in motion of
  particles and fluids orbiting rapidly rotating Kerr black holes   Newton's theory predicts that the velocity $V$ of free test particles on
circular orbits around a spherical gravity center is a decreasing function of
the orbital radius $r$, $dV/dr < 0$. Only very recently, Aschenbach (A&A 425,
p. 1075 (2004)) has shown that, unexpectedly, the same is not true for
particles orbiting black holes: for Kerr black holes with the spin parameter
$a>0.9953$, the velocity has a positive radial gradient for geodesic, stable,
circular orbits in a small radial range close to the black hole horizon. We
show here that the {\em Aschenbach effect} occurs also for non-geodesic
circular orbits with constant specific angular momentum $\ell = \ell_0 =
const$. In Newton's theory it is $V = \ell_0/R$, with $R$ being the cylindrical
radius. The equivelocity surfaces coincide with the $R = const$ surfaces which,
of course, are just co-axial cylinders. It was previously known that in the
black hole case this simple topology changes because one of the ``cylinders''
self-crosses. We show here that the Aschenbach effect is connected to a second
topology change that for the $\ell = const$ tori occurs only for very highly
spinning black holes, $a>0.99979$.

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The categories of this paper are: physics
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The categories of this paper are: funct-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: astro-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: alg-geom