Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: AB Aurigae: Possible evidence of planet formation through the
  gravitational instability   Recent observations of the protoplanetary disc surrounding AB Aurigae have
revealed the possible presence of two giant planets in the process of forming.
The young measured age of $1-4$Myr for this system allows us to place strict
time constraints on the formation histories of the observed planets. Hence we
may be able to make a crucial distinction between formation through core
accretion (CA) or the gravitational instability (GI), as CA formation
timescales are typically Myrs whilst formation through GI will occur within the
first $\approx10^4-10^5$yrs of disc evolution. We focus our analysis on the
$4-13$M$_{\rm Jup}$ planet observed at $R\approx30$AU. We find CA formation
timescales for such a massive planet typically exceed the system's age. The
planet's high mass and wide orbit may instead be indicative of formation
through GI. We use smoothed particle hydrodynamic simulations to determine the
system's critical disc mass for fragmentation, finding $M_{\rm
d,crit}=0.3$M$_{\odot}$. Viscous evolution models of the disc's mass history
indicate that it was likely massive enough to exceed $M_{\rm d,crit}$ in the
recent past, thus it is possible that a young AB Aurigae disc may have
fragmented to form multiple giant gaseous protoplanets. Calculations of the
Jeans mass in an AB Aurigae-like disc find that fragments may initially form
with masses $1.6-13.3$M$_{\rm Jup}$, consistent with the planets which have
been observed. We therefore propose that the inferred planets in the disc
surrounding AB Aurigae may be evidence of planet formation through GI.

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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: math-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: q-fin
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: cond-mat
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The categories of this paper are: physics
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: math