Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The first five years of gravitational-wave astrophysics   Gravitational waves are ripples in spacetime generated by the acceleration of
astrophysical objects. A direct consequence of general relativity, they were
first directly observed in 2015 by the twin Laser Interferometer
Gravitational-Wave Observatory (LIGO) observatories. I review the first five
years of gravitational wave detections. More than fifty gravitational waves
events have been found, emitted by pairs of merging compact objects such as
neutron stars and black holes. These signals yield insights into the formation
of compact objects and their progenitor stars, enable stringent tests of
general relativity and constrain the behavior of matter at densities higher
than an atomic nucleus. Mergers that emit both gravitational and
electromagnetic waves probe the formation of short gamma ray bursts, the
nucleosynthesis of heavy elements, and measure the local expansion rate of the
Universe.

36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int