Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct magnetic field detection in the innermost regions of an accretion
  disc   Models predict that magnetic fields play a crucial role in the physics of
astrophysical accretion disks and their associated winds and jets. For example,
the rotation of the disk twists around the rotation axis the initially vertical
magnetic field, which responds by slowing down the plasma in the disk and by
causing it to fall towards the central star. The magnetic energy flux produced
in this process points away from the disk, pushing the surface plasma outwards,
leading to a wind from the disk and sometimes a collimated jet. But these
predictions have hitherto not been supported by observations. Here we report
the direct detection of the magnetic field in the core of the protostellar
accretion disk FU Orionis. The surface field reaches strengths of about 1 kG
close to the centre of the disk, and it includes a significant azimuthal
component, in good agreement with recent models. But we find that the field is
very filamentary and slows down the disk plasma much more than models predict,
which may explain why FU Ori fails to collimate its wind into a jet.

27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess