Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Astrophysical Evidence for Black Hole Event Horizons   Astronomers have discovered many potential black holes in X-ray binaries and
galactic nuclei. These black holes are usually identified by the fact that they
are too massive to be neutron stars. Until recently, however, there was no
convincing evidence that the objects identified as black hole candidates
actually have event horizons. This has changed with extensive applications of a
class of accretion models for describing the flow of gas onto compact objects;
for these solutions, called advection-dominated accretion flows (ADAFs), the
black hole nature of the accreting star, specifically its event horizon, plays
an important role. We review the evidence that, at low luminosities, accreting
black holes in both X-ray binaries and galactic nuclei contain ADAFs rather
than the standard thin accretion disk.

22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th