https://doi.org/10.1140/epjc/s10052-019-6940-z
Letter
Gravitational waves from binary axionic black holes
1
Université de Nice, Observatoire de la Côte d’Azur, 06304, Nice, France
2
Instituto de Física Gleb Wataghin, UNICAMP, Campinas, SP, 13083-970, Brazil
3
Instituto de Física, Universidade Federal da Bahia, Salvador, Bahia, 40210-340, Brazil
4
Núcleo Cosmo-ufes & Departamento de Física, UFES, Vitória, ES, 29075-910, Brazil
5
National Research Nuclear University MEPhI, 115409, Moscow, Russia
* e-mail: saulo.carneiro.ufba@gmail.com
** e-mail: saulo.carneiro@pq.cnpq.br
Received:
9
November
2018
Accepted:
12
May
2019
Published online:
20
May
2019
In a recent paper we have shown that a minimally coupled, self-interacting scalar field of mass m can form black holes of mass 
(in Planck units). If dark matter is composed by axions, they can form miniclusters that for QCD axions have masses below this value. In this work it is shown that for a scenario in which the axion mass depends on the temperature as 
, minicluster masses above 
, corresponding to an axion mass of 
eV, exceed M and can collapse into black holes. If a fraction of these black holes is in binary systems, gravitational waves emitted during the inspiral phase could be detected by advanced interferometers like LIGO or VIRGO and by the planned Einstein Telescope. For a detection rate of one event per year, the lower limits on the binary fraction are 
and 
for LIGO and Einstein Telescope respectively.
© The Author(s), 2019
