Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Possible Gravitational Microlensing of a Star in the Large Magellanic
  Cloud   There is now abundant evidence for the presence of large quantities of unseen
matter surrounding normal galaxies, including our own$^{1,2}$. The nature of
this `dark matter' is unknown, except that it cannot be made of normal stars,
dust, or gas, as they would be easily detected. Exotic particles such as
axions, massive neutrinos or other weakly interacting massive particles
(collectively known as WIMPs) have been proposed)$^{3,4}$, but have yet to be
detected. A less exotic alternative is normal matter in the form of bodies with
masses ranging from that of a large planet to a few $ \msun$. Such objects,
known collectively as massive compact halo objects$^5$ (MACHOs) might be brown
dwarfs or `Jupiters' (bodies too small to produce their own energy by fusion),
neutron stars, old white dwarfs, or black holes. Paczynski$^6$ suggested that
MACHOs might act as gravitational microlenses, occasionally causing the
apparent brightness of distant background stars temporarily to increase. We are
conducting a microlensing experiment to determine whether the dark matter halo
of our galaxy is made up of MACHOs. Here we report a candidate for a
microlensing event, detected by monitoring the light curves of 1.8 million
stars in the Large Magellanic Cloud for one year. The light curve shows no
variation for most of the year of data taking, and an upward excursion lasting
over 1 month, with a maximum increase of $\approx \bf 2$ mag. The most probable
lens mass, inferred from the duration of the event, is $\bf \sim 0.1 \,\msun$.

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The categories of this paper are: stat
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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: nucl-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
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The categories of this paper are: hep-th
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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: chao-dyn
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom