https://doi.org/10.1140/epja/s10050-019-00018-6
Regular Article - Theoretical Physics
Thermodynamics conditions of matter in the neutrino decoupling region during neutron star mergers
1
Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena, 07743, Jena, Germany
2
Dipartimento di Fisica, Università di Trento, Via Sommarive 14, 38123, Trento, Italy
3
Istituto Nazionale di Fisica Nucleare, Sezione di Milano-Bicocca, Piazza della Scienza, 20100, Milano, Italy
4
Dipartimento di Fisica G. Occhialini, Università di Milano-Bicocca, Piazza della Scienza 3, 20126, Milano, Italy
5
Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ, 08540, USA
6
Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ, 08544, USA
7
INFN-TIFPA, Trento Institute for Fundamental Physics and Applications, Via Sommarive 14, 38123, Trento, Italy
8
Physics Division, Argonne National Laboratory, Argonne, IL, 60439, USA
* e-mail: andrea.endrizzi@uni-jena.de
Received:
18
August
2019
Accepted:
11
November
2019
Published online:
21
January
2020
In this work we investigate the thermodynamics conditions at which neutrinos decouple from matter in neutron star merger remnants by post-processing results of merger simulations. We find that the matter density and the neutrino energies are the most relevant quantities in determining the decoupling surface location. For mean energy neutrinos (
9, 15 and 24 MeV for 
, 
and 
, respectively) the transition between diffusion and free-streaming conditions occurs around 
for all neutrino species. Weak and thermal equilibrium freeze-out occurs deeper (several 
) for heavy-flavor neutrinos than for and (
). Decoupling temperatures are broadly in agreement with the average neutrino energies, with softer equations of state characterized by 1 MeV larger decoupling temperatures. Neutrinos streaming at infinity with different energies come from different remnant parts. While low-energy neutrinos (
) decouple at 
, 
and 
close to weak equilibrium, high-energy ones (
) decouple from the disk at 
, 
and 
. The presence of a massive NS or a BH influences the neutrino thermalization. While in the former case decoupling surfaces are present for all relevant energies, the lower maximum density (
) in BH-torus systems does not allow softer neutrinos to thermalize and diffuse.
© The Author(s), 2020
