Issue |
A&A
Volume 689, September 2024
|
|
---|---|---|
Article Number | A300 | |
Number of page(s) | 11 | |
Section | Numerical methods and codes | |
DOI | https://doi.org/10.1051/0004-6361/202449849 | |
Published online | 20 September 2024 |
Numerical challenges for energy conservation in N-body simulations of collapsing self-interacting dark matter halos
1
Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München,
Scheinerstr. 1,
81679
München,
Germany
2
Excellence Cluster ORIGINS,
Boltzmannstrasse 2,
85748
Garching,
Germany
3
Max-Planck-Institut für Astrophysik,
Karl-Schwarzschild-Str. 1,
85748
Garching,
Germany
4
Department of Physics and Astronomy, University of California,
Riverside,
California
92521,
USA
Received:
4
March
2024
Accepted:
13
August
2024
Context. Dark matter (DM) halos can be subject to gravothermal collapse if the DM is not collisionless, but engaged in strong self-interactions instead. When the scattering is able to efficiently transfer heat from the centre to the outskirts, the central region of the halo collapses and reaches densities much higher than those for collisionless DM. This phenomenon is potentially observable in studies of strong lensing. Current theoretical efforts are motivated by observations of surprisingly dense substructures. However, a comparison with observations requires accurate predictions. One method to obtain such predictions is to use N-body simulations. Collapsed halos are extreme systems that pose severe challenges when applying state-of-the-art codes to model self-interacting dark matter (SIDM).
Aims. In this work, we investigate the root of such problems, with a focus on energy non-conservation. Moreover, we discuss possible strategies to avoid them.
Methods. We ran N-body simulations, both with and without SIDM, of an isolated DM-only halo and we adjusted the numerical parameters to check the accuracy of the simulation.
Results. We find that not only the numerical scheme for SIDM can lead to energy non-conservation, but also the modelling of gravitational interaction and the time integration are problematic. The main issues we find are: (a) particles changing their time step in a non-time-reversible manner; (b) the asymmetry in the tree-based gravitational force evaluation; and (c) SIDM velocity kicks breaking the time symmetry.
Conclusions. Tuning the parameters of the simulation to achieve a high level of accuracy allows us to conserve energy not only at early stages of the evolution, but also later on. However, the cost of the simulations becomes prohibitively large as a result. Some of the problems that make the simulations of the gravothermal collapse phase inaccurate can be overcome by choosing appropriate numerical schemes. However, other issues still pose a challenge. Our findings motivate further works on addressing the challenges in simulating strong DM self-interactions.
Key words: methods: numerical / dark matter
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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