Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Compact Radio Cores in the Galactic Center and Elsewhere   Compact radio cores are not only common in radio galaxies and quasars but
also in many nearby galaxies with low-active, supermassive black holes. One
famous example is the Galactic Center source Sgr A*. Recent studies of proper
motions and radial velocities of stars in the inner parsec of the Galaxy
convincingly demonstrate the presence of a compact dark mass of 2.5 10^6 Mo in
the nucleus of the Milky Way. Millimeter VLBI and submm observations of Sgr A*
thus probe a region of only a few Schwarzschild radii in diameter. In this
paper I will review our current theoretical and observational knowledge of this
source and compare it to some famous LINER galaxies like NGC 4258, NGC 3079,
and NGC 6500. In all cases these radio cores can be well explained by a
standard AGN jet model, and, with the exception of Sgr A*, large scale outflows
are observed that have powers comparable to those inferred from the radio
cores. Recent VLBI observations of radio-weak quasars and HST observations of
Seyfert galaxies indicate that these AGN also produce powerful jets which,
however, have relatively less luminous radio cores than radio-loud quasars and
the LINERs discussed here. Therefore, jets and compact radio cores appear to be
natural constituents of an AGN, but the reason why apparently some jets are
radio-loud and others not remains a mystery.

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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: supr-con
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ph
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The categories of this paper are: q-bio
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The categories of this paper are: q-alg
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The categories of this paper are: math
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The categories of this paper are: plasm-ph
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-th