Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Four annular structures in a protostellar disk less than 500,000 years
  old   Annular structures, or rings and gaps, in disks around pre-main sequence
stars have been detected in abundance towards Class II objects ~1,000,000 years
in age. These structures are often interpreted as evidence of planet formation,
with planet-mass bodies carving rings and gaps in the disk. This implies that
planet formation may already be underway in even younger disks in the Class I
phase, when the protostar is still embedded in a larger scale dense envelope of
gas and dust. While younger disks likely play an important role in the onset of
planet formation, only within the past decade have detailed properties of disks
in the youngest star-forming phases begun to be observed. Here we present 1.3
mm dust emission observations with 5 au resolution that show four annular
substructures in the disk of the young (<500,000 years) protostar IRS 63. IRS
63, a single Class I source located in the nearby Ophiuchus molecular cloud (at
a distance of 144 pc), is one of the brightest Class I protostars at
(sub)millimeter wavelengths that also has a relatively large disk (>50 au).
Multiple annular substructures observed towards disks at young times can act as
an early foothold for dust grain growth, a prerequisite of planet formation.
Whether planets already exist or not in the disk of IRS 63, it is clear that
the planet formation process begins in the young protostellar phases, earlier
than predicted by current planet formation theories.

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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: econ
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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org
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The categories of this paper are: atom-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
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The categories of this paper are: q-bio