Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Black hole demography at the dawn of gravitational-wave astronomy: state
  of the art and future perspectives   The first LIGO-Virgo detections have confirmed the existence of massive black
holes (BHs), with mass $30-40$ M$_\odot$. Such BHs might originate from massive
metal-poor stars ($Z<0.3$ Z$_\odot$) or from gravitational instabilities in the
early Universe. The formation channels of merging BHs are still poorly
constrained. The measure of mass, spin and redshift distribution of merging BHs
will give us fundamental clues to distinguish between different models. Also, a
better understanding of several astrophysical processes (e.g. common envelope,
core-collapse supernovae, and dynamical evolution of BHs) is decisive, to shed
light on the formation channels of merging BHs.

20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th