Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Protostellar Disks: Formation, Fragmentation, and the Brown Dwarf Desert   We argue that gravitational instability of typical protostellar disks is not
a viable mechanism for the fragmentation into multiple systems -- binary stars,
brown dwarf companions, or gas giant planets -- except at periods above roughly
20,000 years. Our conclusion is based on a comparison between prior numerical
work on disk self-gravity by Gammie (2001) with our own analytical models for
the dynamical and thermal state of protostellar disks. For this purpose we
first develop a simple theory for the initial conditions of low-mass star
formation, accounting for the effect of turbulence on the characteristic mass,
accretion rate, and angular momentum of collaping cores. Second, we examine the
criterion for fragmentation to occur during star formation, concentrating on
the self-gravitational instabilities of protostellar accretion disks in their
main accretion phase. Self-gravitational instabilities are strongly dependent
on the thermal state of the disk, and we find that the combination of viscous
heating and stellar irradiation quenches fragmentation due to Toomre's local
instability. Global instability of the disk may be required to process mass
supply, but is unlikely to produce fragments. Our findings help to explain the
dearth of substellar companions to stellar type stars: the brown dwarf desert.

8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom