Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A STRINGENT CONSTRAINT ON ALTERNATIVES TO A MASSIVE BLACK HOLE AT THE
  CENTER OF NGC 4258   There is now dynamical evidence for massive dark objects at the center of
several galaxies, but suggestions that these are supermassive black holes are
based only on indirect astrophysical arguments. The recent unprecedented
measurement of the rotation curve of maser emission sources at the center of
NGC 4258, and the remarkable discovery that it is Keplerian to high precision,
provides us a unique opportunity for testing alternatives to a BH (e.g., a
massive cluster of stellar remnants, brown dwarfs, low-mass stars, or halo dark
matter).
  We use a conservative upper limit on the systematic deviation from a
Keplerian rotation curve to constrain the mass distribution at the galaxy
center. Based on evaporation and physical collision time-scale arguments, we
show that a central cluster is ruled out, *unless* the cluster consists of
*extremely* dense objects with mass less than about 0.05 solar masses (e.g.,
low mass BHs or elementary particles). Since both of these dynamically-allowed
systems are very improbable for other astrophysical reasons, we conclude that a
central dense cluster at the center of NGC 4258 is *very* improbable, thus
leaving the alternative possibility of a massive BH. We also show that the mass
of the BH must be at least 98% of the mass enclosed within the inner edge of
the masering disk (3.6*10^7 solar masses). A substantial contribution to that
mass from a density cusp in the background mass distribution is excluded.

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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: cond-mat
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The categories of this paper are: q-fin
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The categories of this paper are: ao-sci
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: math-ph
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The categories of this paper are: econ
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-th