Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The runaway black hole GRO J1655-40   We have used the Hubble Space Telescope to measure the motion in the sky and
compute the galactocentric orbit of the black hole X-ray binary GRO J1655-40.
The system moves with a runaway space velocity of $112\pm 18$ km s$^{-1}$ in a
highly eccentric ($e = 0.34\pm 0.05$) orbit. The black hole was formed in the
disk at a distance greater than 3 kpc from the Galactic centre and must have
been shot to such an eccentric orbit by the explosion of the progenitor star.
The runaway linear momentum and kinetic energy of this black hole binary are
comparable to those of solitary neutron stars and millisecond pulsars. GRO
J1655-40 is the first black hole for which there is evidence for a runaway
motion imparted by a natal kick in a supernova explosion.

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The categories of this paper are: adap-org
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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: stat
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The categories of this paper are: math
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
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The categories of this paper are: q-alg
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The categories of this paper are: econ
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: hep-ph