Colliding clusters and dark matter self-interactions
Open accessAbstract
When a dark matter halo moves through a background of dark matter particles, self-interactions can lead to both deceleration and evaporation of the halo and thus shift its centroid relative to the collisionless stars and galaxies. We study the magnitude and time evolution of this shift for two classes of dark matter self-interactions, namely frequent self-interactions with small momentum transfer (e.g. due to long-range interactions) and rare self-interactions with large momentum transfer (e.g. contact interactions), and find important differences between the two cases. We find that neither effect can be strong enough to completely separate the dark matter halo from the galaxies, if we impose conservative bounds on the self-interaction cross-section. The majority of both populations remain bound to the same gravitational potential, and the peaks of their distributions are therefore always coincident. Consequently, any apparent separation is mainly due to particles which are leaving the gravitational potential, so will be largest shortly after the collision but not observable in evolved systems. Nevertheless, the fraction of collisions with large momentum transfer is an important characteristic of self-interactions, which can potentially be extracted from observational data and provide an important clue as to the nature of dark matter.
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SIDM simulations show a low-density bridge forming between the two peaks after first pericenter in a bimodal merger, which shifts the centroid but not the peak, which stays with the galaxies.
“In fact, SIDM simulations (Kahlhoefer et al. 2014;Kim et al. 2016;Robertson et al. 2017) show a low-density bridge forming between the two peaks after first pericenter in a bimodal merger.This shifts the centroid but not the peak, which stays with the galaxies.”
From The Mismeasure of Mergers: Revised Limits on Self-interacting Dark Matter in Merging Galaxy Clusters (2018) · cites this paper as Kahlhoefer et al. (2014)
Section 4 (p. 10) reports that differing tails separate the dark-matter and galaxy centroids while their peaks remain coincident; Section 5 (p. 12) reiterates this result. The paper does not describe a low-density bridge between the two cluster peaks, so that specific feature is not supported by this source. (LLM, conf=0.85)
Experimental — accuracy not yet measuredPrevious studies have focused on mass-galaxy offsets, which numerical simulations have shown to be intrinsically small because galaxies remain tightly coupled to the dominant dark matter potential even with significant self-interaction.
“However, previous studies have focused on mass-galaxy offsets, which numerical simulations have shown to be intrinsically small because galaxies remain tightly coupled to the dominant dark matter potential even with significant self-interaction.”
From A New Robust Constraint on the Self-interaction Cross Section of Dark Matter with Double Radio Relic Clusters (2026) · cites this paper as F.Kahlhoefer et al. 2014
Even in the presence of a nonzero cross section, the expected mass-galaxy offset is frequently too small to be detected with current observational precision.
“Furthermore, numerical simulations have shown that even in the presence of a nonzero cross section, the expected massgalaxy offset is frequently too small to be detected with current observational precision (F.Kahlhoefer et al. 2014).”
From A New Robust Constraint on the Self-interaction Cross Section of Dark Matter with Double Radio Relic Clusters (2026) · cites this paper as F.Kahlhoefer et al. 2014
Cluster mergers can also be used to test SIDM effects that cannot be modeled with a drag force; as noted by Kahlhoefer et al. (2014), the drag-force model maps well to frequent interactions with low momentum transfer, as in a long-range force.
“Cluster mergers can also be used to test SIDM effects that cannot be modeled with a drag force; as noted by Kahlhoefer et al. (2014), the drag-force model maps well to frequent interactions with low momentum transfer, as in a long-range force.”
From The Mismeasure of Mergers: Revised Limits on Self-interacting Dark Matter in Merging Galaxy Clusters (2018) · cites this paper as Kahlhoefer et al. (2014)
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Cites
Galactic Dynamics: Second Edition
Binney, J., & Tremaine, S. (2008) · doi:10.1515/9781400828722 · Cited by 4,375 · cited 2× · see citing works
“The isochrone model is defined by the potential (Binney & Tremaine 2008) (r) = − GNM b + √b2 + r2 .”
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Research works printed but not linked: 9
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The Mismeasure of Mergers: Revised Limits on Self-interacting Dark Matter in Merging Galaxy Clusters
Wittman, D., Golovich, N., & Dawson, W. A. (2018) · The Astrophysical Journal · doi:10.3847/1538-4357/aaee77 · Cited by 80 · see citing works
Jee, M. J., Park, D., & Lee, W. (2026) · The Astrophysical Journal · doi:10.3847/1538-4357/ae88fb · Cited by 1 · see citing works
- Authors
- Kahlhoefer, F., Schmidt-Hoberg, K., Frandsen, M. T., & Sarkar, S.
- Affiliations
- University of Oxford (GB)
- European Organization for Nuclear Research (CH)
- University of Southern Denmark (DK)
- University of Copenhagen (DK)
- Venue
- Monthly Notices of the Royal Astronomical Society
- Publisher
- Oxford University Press (OUP)
- Published
- 2013-11-26
- Volume
- 437
- Issue
- 3
- Pages
- 2865-2881
- ISSN
- 0035-8711 (ISSN-L)
- 1365-2966
- OpenAlex
- W2013744410
- Cited by
- 207
- References
- 1
- Citations by year
- 2026: 9 · 2025: 14 · 2024: 11 · 2023: 14 · 2022: 17 · 2021: 18 · 2020: 19 · 2019: 15 · 2018: 24 · 2017: 22 · 2016: 16 · 2015: 18 · 2014: 9 · 2013: 1
- FWCI
- 6.03
- Type
- journal article
- Language
- en
- Open access
- green
- arxiv.org
- Locations
- Monthly Notices of the Royal Astronomical Society (publishedVersion)
- Oxford University Research Archive (ORA) (University of Oxford) (publishedVersion)
- arXiv (Cornell University) (acceptedVersion)
- University of Southern Denmark Research Portal (University of Southern Denmark) (submittedVersion)
- CERN Document Server (European Organization for Nuclear Research) (submittedVersion, cc-by)
- Desy Publications Database (Deutsches Elektronen-Synchrotron DESY) (submittedVersion, other-oa)
- Research at the University of Copenhagen (University of Copenhagen) (submittedVersion)
- arXiv (Cornell University)
- DESY Publication Database (PUBDB) (Deutsches Elektronen-Synchrotron)
- Funders
- National Science Foundation (PHY11- 25915, 25915)
- European Commission (237920)
- National Research Foundation (120829)
- Deutsche Forschungsgemeinschaft
- Danmarks Grundforskningsfond (25915)
- Studienstiftung des Deutschen Volkes
- Danmarks Frie Forskningsfond (11-120829)
- Science and Technology Facilities Council (ST/J000507/1, ST/L000474/1)
- Kavli Institute for Theoretical Physics, University of California, Santa Barbara (PHY-11-25915)
- Topics
- Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Dark Matter and Cosmic Phenomena
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
- Keywords
- dark matter self-interaction, dark matter halos, long-range interactions, contact interaction, momentum transfer
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