Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A new evolutionary scenario for the formation of massive black-hole
  binaries such as M33 X-7 and IC 10 X-1   The formation of close massive black-hole binaries is a challenge for binary
evolutionary models, especially the intriguing system M33 X-7 which harbours
one of the most massive stellar-mass black holes (16 solar masses) orbiting a
70 solar mass O-star every 3.5 days. In standard binary evolution theory an
episode of mass transfer or common envelope is inevitable in a binary with such
a small orbital period, which complicates the formation of a black hole with
such a high mass.
  To explain this system, we discuss a new binary evolution channel (De Mink et
al. 2009), in which rotational mixing plays an important role. In very massive
close binaries, tides force the rotation rate of the stars to be so high that
rotationally induced mixing becomes very efficient. Helium produced in the
center is mixed throughout the envelope. Instead of expanding during their
mainsequence evolution (with the inevitable consequence of mass transfer),
these stars stay compact, and avoid filling their Roche lobe. They gradually
evolve into massive helium stars. This scenario naturally leads to the
formation of very massive black holes in a very close orbit with a less evolved
massive companion such as M33 X-7.

27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an